{"thread":{"id":"50834","subject":"[PATCH 0/4] trace2: load trace2 settings from system config","startedAt":"2019-03-28T13:31:00Z","lastAt":"2019-05-07T01:18:20Z","messageCount":68,"participants":["Jeff Hostetler via GitGitGadget","Ævar Arnfjörð Bjarmason","Jeff Hostetler","Josh Steadmon","Jonathan Nieder","Junio C Hamano","Johannes Schindelin","SZEDER Gábor"],"isPatch":true,"patchVersion":1,"patchTotal":4},"messages":[{"id":"372614","messageId":"pull.169.git.gitgitgadget@gmail.com","threadId":"50834","inReplyTo":null,"subject":"[PATCH 0/4] trace2: load trace2 settings from system config","fromName":"Jeff Hostetler via GitGitGadget","fromEmail":"gitgitgadget@gmail.com","sentAt":"2019-03-28T13:30:52Z","receivedAt":"2019-03-28T13:31:00Z","isPatch":true,"sender":{"key":"git@jeffhostetler.com","avatar":null},"body":"Teach git to load default Trace2 settings from the system config (usually\n\"/etc/gitconfig\"). The existing GIT_TR2_* environment variables can be used\nto override the new system defaults. It also includes a little startup\nrefactoring.\n\nNote: I found interactive testing of this feature to be awkward on some\nplatforms because of the use of prefix- or runtime-prefix-relative locations\nfor the system configuration. It was easy to accidentally use an officially\ninstalled version of git to set a system config variable in the official\nsystem config directory; and then when testing with the test version of git,\nthat value would not be seen because it was looking for the system config\nfile in a different directory.\n\nJeff Hostetler (4):\n trace2: refactor setting process starting time\n trace2: add absolute elapsed time to start event\n trace2: find exec-dir before trace2 initialization\n trace2: use system config for default trace2 settings\n\n Documentation/technical/api-trace2.txt | 54 +++++++++--\n Makefile | 1 +\n common-main.c | 6 +-\n compat/mingw.c | 2 +\n t/t0210-trace2-normal.sh | 41 +++++++-\n t/t0211-trace2-perf.sh | 53 ++++++++---\n t/t0212-trace2-event.sh | 52 +++++++++-\n trace2.c | 19 +++-\n trace2.h | 24 ++++-\n trace2/tr2_cfg.c | 7 +-\n trace2/tr2_dst.c | 24 ++---\n trace2/tr2_dst.h | 3 +-\n trace2/tr2_sysenv.c | 125 +++++++++++++++++++++++++\n trace2/tr2_sysenv.h | 36 +++++++\n trace2/tr2_tgt.h | 1 +\n trace2/tr2_tgt_event.c | 24 ++---\n trace2/tr2_tgt_normal.c | 13 +--\n trace2/tr2_tgt_perf.c | 17 ++--\n trace2/tr2_tls.c | 38 +++++---\n trace2/tr2_tls.h | 8 +-\n 20 files changed, 455 insertions(+), 93 deletions(-)\n create mode 100644 trace2/tr2_sysenv.c\n create mode 100644 trace2/tr2_sysenv.h\n\n\nbase-commit: 041f5ea1cf987a4068ef5f39ba0a09be85952064\nPublished-As: https://github.com/gitgitgadget/git/releases/tag/pr-169%2Fjeffhostetler%2Fcore-tr2-startup-and-sysenv-v1\nFetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-169/jeffhostetler/core-tr2-startup-and-sysenv-v1\nPull-Request: https://github.com/gitgitgadget/git/pull/169\n-- \ngitgitgadget\n"},{"id":"372615","messageId":"7f1a34732271f9fbdbec0f4cd0a5990466ebd071.1553779851.git.gitgitgadget@gmail.com","threadId":"50834","inReplyTo":"pull.169.git.gitgitgadget@gmail.com","subject":"[PATCH 1/4] trace2: refactor setting process starting time","fromName":"Jeff Hostetler via GitGitGadget","fromEmail":"gitgitgadget@gmail.com","sentAt":"2019-03-28T13:30:57Z","receivedAt":"2019-03-28T13:31:03Z","isPatch":true,"sender":{"key":"git@jeffhostetler.com","avatar":null},"body":"From: Jeff Hostetler \n\nCreate trace2_initialize_clock() and call from main() to capture\nprocess start time in isolation and before other sub-systems are\nready.\n\nSigned-off-by: Jeff Hostetler \n---\n Documentation/technical/api-trace2.txt | 12 ++++++--\n common-main.c | 2 ++\n compat/mingw.c | 2 ++\n trace2.c | 7 ++++-\n trace2.h | 17 ++++++++++++\n trace2/tr2_tls.c | 38 ++++++++++++++++----------\n trace2/tr2_tls.h | 8 +++++-\n 7 files changed, 67 insertions(+), 19 deletions(-)\n\ndiff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt\nindex 2de565fa3d..f37fccf1da 100644\n--- a/Documentation/technical/api-trace2.txt\n+++ b/Documentation/technical/api-trace2.txt\n@@ -160,17 +160,23 @@ purposes.\n \n These are concerned with the lifetime of the overall git process.\n \n+`void trace2_initialize_clock()`::\n+\n+\tInitialize the Trace2 start clock and nothing else. This should\n+\tbe called at the very top of main() to capture the process start\n+\ttime and reduce startup order dependencies.\n+\n `void trace2_initialize()`::\n \n \tDetermines if any Trace2 Targets should be enabled and\n-\tinitializes the Trace2 facility. This includes starting the\n-\telapsed time clocks and thread local storage (TLS).\n+\tinitializes the Trace2 facility. This includes setting up the\n+\tTrace2 thread local storage (TLS).\n +\n This function emits a \"version\" message containing the version of git\n and the Trace2 protocol.\n +\n This function should be called from `main()` as early as possible in\n-the life of the process.\n+the life of the process after essential process initialization.\n \n `int trace2_is_enabled()`::\n \ndiff --git a/common-main.c b/common-main.c\nindex d484aec209..6137af0e63 100644\n--- a/common-main.c\n+++ b/common-main.c\n@@ -27,6 +27,8 @@ int main(int argc, const char **argv)\n {\n \tint result;\n \n+\ttrace2_initialize_clock();\n+\n \t/*\n \t * Always open file descriptors 0/1/2 to avoid clobbering files\n \t * in die(). It also avoids messing up when the pipes are dup'ed\ndiff --git a/compat/mingw.c b/compat/mingw.c\nindex 6b04514cdc..a2f74aca6a 100644\n--- a/compat/mingw.c\n+++ b/compat/mingw.c\n@@ -2569,6 +2569,8 @@ void mingw_startup(void)\n \twchar_t **wenv, **wargv;\n \t_startupinfo si;\n \n+\ttrace2_initialize_clock();\n+\n \tmaybe_redirect_std_handles();\n \n \t/* get wide char arguments and environment */\ndiff --git a/trace2.c b/trace2.c\nindex ccccd4ef09..6dd51e6aa5 100644\n--- a/trace2.c\n+++ b/trace2.c\n@@ -142,6 +142,11 @@ static void tr2main_signal_handler(int signo)\n \traise(signo);\n }\n \n+void trace2_initialize_clock(void)\n+{\n+\ttr2tls_start_process_clock();\n+}\n+\n void trace2_initialize_fl(const char *file, int line)\n {\n \tstruct tr2_tgt *tgt_j;\n@@ -428,7 +433,7 @@ void trace2_thread_start_fl(const char *file, int line, const char *thread_name)\n \tus_now = getnanotime() / 1000;\n \tus_elapsed_absolute = tr2tls_absolute_elapsed(us_now);\n \n-\ttr2tls_create_self(thread_name);\n+\ttr2tls_create_self(thread_name, us_now);\n \n \tfor_each_wanted_builtin (j, tgt_j)\n \t\tif (tgt_j->pfn_thread_start_fl)\ndiff --git a/trace2.h b/trace2.h\nindex ae5020d0e6..8f89e70c44 100644\n--- a/trace2.h\n+++ b/trace2.h\n@@ -19,6 +19,23 @@ struct json_writer;\n * [] trace2_printf* -- legacy trace[1] messages.\n */\n \n+/*\n+ * Initialize the TRACE2 clock and do nothing else, in particular\n+ * no mallocs, no system inspection, and no environment inspection.\n+ *\n+ * This should be called at the very top of main() to capture the\n+ * process start time. This is intended to reduce chicken-n-egg\n+ * bootstrap pressure.\n+ *\n+ * It is safe to call this more than once. This allows capturing\n+ * absolute startup costs on Windows which uses a little trickery\n+ * to do setup work before common-main.c:main() is called.\n+ *\n+ * The main trace2_initialize_fl() may be called a little later\n+ * after more infrastructure is established.\n+ */\n+void trace2_initialize_clock(void);\n+\n /*\n * Initialize TRACE2 tracing facility if any of the builtin TRACE2\n * targets are enabled in the environment. Emits a 'version' event.\ndiff --git a/trace2/tr2_tls.c b/trace2/tr2_tls.c\nindex 8e65b0361d..31fb529f93 100644\n--- a/trace2/tr2_tls.c\n+++ b/trace2/tr2_tls.c\n@@ -10,16 +10,30 @@\n #define TR2_REGION_NESTING_INITIAL_SIZE (100)\n \n static struct tr2tls_thread_ctx *tr2tls_thread_main;\n-static uint64_t tr2tls_us_start_main;\n+static uint64_t tr2tls_us_start_process;\n \n static pthread_mutex_t tr2tls_mutex;\n static pthread_key_t tr2tls_key;\n \n static int tr2_next_thread_id; /* modify under lock */\n \n-struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name)\n+void tr2tls_start_process_clock(void)\n+{\n+\tif (tr2tls_us_start_process)\n+\t\treturn;\n+\n+\t/*\n+\t * Keep the absolute start time of the process (i.e. the main\n+\t * process) in a fixed variable since other threads need to\n+\t * access it. This allows them to do that without a lock on\n+\t * main thread's array data (because of reallocs).\n+\t */\n+\ttr2tls_us_start_process = getnanotime() / 1000;\n+}\n+\n+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,\n+\t\t\t\t\t uint64_t us_thread_start)\n {\n-\tuint64_t us_now = getnanotime() / 1000;\n \tstruct tr2tls_thread_ctx *ctx = xcalloc(1, sizeof(*ctx));\n \n \t/*\n@@ -29,7 +43,7 @@ struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name)\n \t */\n \tctx->alloc = TR2_REGION_NESTING_INITIAL_SIZE;\n \tctx->array_us_start = (uint64_t *)xcalloc(ctx->alloc, sizeof(uint64_t));\n-\tctx->array_us_start[ctx->nr_open_regions++] = us_now;\n+\tctx->array_us_start[ctx->nr_open_regions++] = us_thread_start;\n \n \tctx->thread_id = tr2tls_locked_increment(&tr2_next_thread_id);\n \n@@ -55,7 +69,7 @@ struct tr2tls_thread_ctx *tr2tls_get_self(void)\n \t * here and silently continue.\n \t */\n \tif (!ctx)\n-\t\tctx = tr2tls_create_self(\"unknown\");\n+\t\tctx = tr2tls_create_self(\"unknown\", getnanotime() / 1000);\n \n \treturn ctx;\n }\n@@ -124,22 +138,18 @@ uint64_t tr2tls_absolute_elapsed(uint64_t us)\n \tif (!tr2tls_thread_main)\n \t\treturn 0;\n \n-\treturn us - tr2tls_us_start_main;\n+\treturn us - tr2tls_us_start_process;\n }\n \n void tr2tls_init(void)\n {\n+\ttr2tls_start_process_clock();\n+\n \tpthread_key_create(&tr2tls_key, NULL);\n \tinit_recursive_mutex(&tr2tls_mutex);\n \n-\ttr2tls_thread_main = tr2tls_create_self(\"main\");\n-\t/*\n-\t * Keep a copy of the absolute start time of the main thread\n-\t * in a fixed variable since other threads need to access it.\n-\t * This also eliminates the need to lock accesses to the main\n-\t * thread's array (because of reallocs).\n-\t */\n-\ttr2tls_us_start_main = tr2tls_thread_main->array_us_start[0];\n+\ttr2tls_thread_main = tr2tls_create_self(\"main\",\n+\t\t\t\t\t\ttr2tls_us_start_process);\n }\n \n void tr2tls_release(void)\ndiff --git a/trace2/tr2_tls.h b/trace2/tr2_tls.h\nindex bb80e3f8e7..b1e327a928 100644\n--- a/trace2/tr2_tls.h\n+++ b/trace2/tr2_tls.h\n@@ -31,7 +31,8 @@ struct tr2tls_thread_ctx {\n * In this and all following functions the term \"self\" refers to the\n * current thread.\n */\n-struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name);\n+struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,\n+\t\t\t\t\t uint64_t us_thread_start);\n \n /*\n * Get our TLS data.\n@@ -94,4 +95,9 @@ void tr2tls_release(void);\n */\n int tr2tls_locked_increment(int *p);\n \n+/*\n+ * Capture the process start time and do nothing else.\n+ */\n+void tr2tls_start_process_clock(void);\n+\n #endif /* TR2_TLS_H */\n-- \ngitgitgadget\n\n"},{"id":"372616","messageId":"c15f783c26ea426688b488c2522dd9c9072cc1bf.1553779851.git.gitgitgadget@gmail.com","threadId":"50834","inReplyTo":"pull.169.git.gitgitgadget@gmail.com","subject":"[PATCH 2/4] trace2: add absolute elapsed time to start event","fromName":"Jeff Hostetler via GitGitGadget","fromEmail":"gitgitgadget@gmail.com","sentAt":"2019-03-28T13:31:00Z","receivedAt":"2019-03-28T13:31:05Z","isPatch":true,"sender":{"key":"git@jeffhostetler.com","avatar":null},"body":"From: Jeff Hostetler \n\nAdd elapsed process time to \"start\" event to measure\nthe performance of early process startup.\n\nSigned-off-by: Jeff Hostetler \n---\n Documentation/technical/api-trace2.txt | 11 ++++++-----\n t/t0211-trace2-perf.sh | 12 ++++++------\n trace2.c | 8 +++++++-\n trace2/tr2_tgt.h | 1 +\n trace2/tr2_tgt_event.c | 5 ++++-\n trace2/tr2_tgt_normal.c | 3 ++-\n trace2/tr2_tgt_perf.c | 7 ++++---\n 7 files changed, 30 insertions(+), 17 deletions(-)\n\ndiff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt\nindex f37fccf1da..baaa1153bb 100644\n--- a/Documentation/technical/api-trace2.txt\n+++ b/Documentation/technical/api-trace2.txt\n@@ -60,7 +60,7 @@ git version 2.20.1.155.g426c96fcdb\n ------------\n $ cat ~/log.perf\n 12:28:42.620675 common-main.c:38 | d0 | main | version | | | | | 2.20.1.155.g426c96fcdb\n-12:28:42.621001 common-main.c:39 | d0 | main | start | | | | | git version\n+12:28:42.621001 common-main.c:39 | d0 | main | start | | 0.001173 | | | git version\n 12:28:42.621111 git.c:432 | d0 | main | cmd_name | | | | | version (version)\n 12:28:42.621225 git.c:662 | d0 | main | exit | | 0.001227 | | | code:0\n 12:28:42.621259 trace2/tr2_tgt_perf.c:211 | d0 | main | atexit | | 0.001265 | | | code:0\n@@ -79,7 +79,7 @@ git version 2.20.1.155.g426c96fcdb\n ------------\n $ cat ~/log.event\n {\"event\":\"version\",\"sid\":\"1547659722619736-11614\",\"thread\":\"main\",\"time\":\"2019-01-16 17:28:42.620713\",\"file\":\"common-main.c\",\"line\":38,\"evt\":\"1\",\"exe\":\"2.20.1.155.g426c96fcdb\"}\n-{\"event\":\"start\",\"sid\":\"1547659722619736-11614\",\"thread\":\"main\",\"time\":\"2019-01-16 17:28:42.621027\",\"file\":\"common-main.c\",\"line\":39,\"argv\":[\"git\",\"version\"]}\n+{\"event\":\"start\",\"sid\":\"1547659722619736-11614\",\"thread\":\"main\",\"time\":\"2019-01-16 17:28:42.621027\",\"file\":\"common-main.c\",\"line\":39,\"t_abs\":0.001173,\"argv\":[\"git\",\"version\"]}\n {\"event\":\"cmd_name\",\"sid\":\"1547659722619736-11614\",\"thread\":\"main\",\"time\":\"2019-01-16 17:28:42.621122\",\"file\":\"git.c\",\"line\":432,\"name\":\"version\",\"hierarchy\":\"version\"}\n {\"event\":\"exit\",\"sid\":\"1547659722619736-11614\",\"thread\":\"main\",\"time\":\"2019-01-16 17:28:42.621236\",\"file\":\"git.c\",\"line\":662,\"t_abs\":0.001227,\"code\":0}\n {\"event\":\"atexit\",\"sid\":\"1547659722619736-11614\",\"thread\":\"main\",\"time\":\"2019-01-16 17:28:42.621268\",\"file\":\"trace2/tr2_tgt_event.c\",\"line\":163,\"t_abs\":0.001265,\"code\":0}\n@@ -601,6 +601,7 @@ from all events and the `time` field is only present on the \"start\" and\n {\n \t\"event\":\"start\",\n \t...\n+\t\"t_abs\":0.001227, # elapsed time in seconds\n \t\"argv\":[\"git\",\"version\"]\n }\n ------------\n@@ -1118,7 +1119,7 @@ $ git status\n \n $ cat ~/log.perf\n d0 | main | version | | | | | 2.20.1.160.g5676107ecd.dirty\n-d0 | main | start | | | | | git status\n+d0 | main | start | | 0.001173 | | | git status\n d0 | main | def_repo | r1 | | | | worktree:/Users/jeffhost/work/gfw\n d0 | main | cmd_name | | | | | status (status)\n ...\n@@ -1163,7 +1164,7 @@ $ git status\n ...\n $ cat ~/log.perf\n d0 | main | version | | | | | 2.20.1.162.gb4ccea44db.dirty\n-d0 | main | start | | | | | git status\n+d0 | main | start | | 0.001173 | | | git status\n d0 | main | def_repo | r1 | | | | worktree:/Users/jeffhost/work/gfw\n d0 | main | cmd_name | | | | | status (status)\n ...\n@@ -1219,7 +1220,7 @@ $ git status\n ...\n $ cat ~/log.perf\n d0 | main | version | | | | | 2.20.1.156.gf9916ae094.dirty\n-d0 | main | start | | | | | git status\n+d0 | main | start | | 0.001173 | | | git status\n d0 | main | def_repo | r1 | | | | worktree:/Users/jeffhost/work/gfw\n d0 | main | cmd_name | | | | | status (status)\n d0 | main | region_enter | r1 | 0.001791 | | index | label:do_read_index .git/index\ndiff --git a/t/t0211-trace2-perf.sh b/t/t0211-trace2-perf.sh\nindex 953e2f7847..c9694b29f7 100755\n--- a/t/t0211-trace2-perf.sh\n+++ b/t/t0211-trace2-perf.sh\n@@ -50,7 +50,7 @@ test_expect_success 'perf stream, return code 0' '\n \tperl \"$TEST_DIRECTORY/t0211/scrub_perf.perl\" actual &&\n \tcat >expect <<-EOF &&\n \t\td0|main|version|||||$V\n-\t\td0|main|start|||||_EXE_ trace2 001return 0\n+\t\td0|main|start||_T_ABS_|||_EXE_ trace2 001return 0\n \t\td0|main|cmd_name|||||trace2 (trace2)\n \t\td0|main|exit||_T_ABS_|||code:0\n \t\td0|main|atexit||_T_ABS_|||code:0\n@@ -64,7 +64,7 @@ test_expect_success 'perf stream, return code 1' '\n \tperl \"$TEST_DIRECTORY/t0211/scrub_perf.perl\" actual &&\n \tcat >expect <<-EOF &&\n \t\td0|main|version|||||$V\n-\t\td0|main|start|||||_EXE_ trace2 001return 1\n+\t\td0|main|start||_T_ABS_|||_EXE_ trace2 001return 1\n \t\td0|main|cmd_name|||||trace2 (trace2)\n \t\td0|main|exit||_T_ABS_|||code:1\n \t\td0|main|atexit||_T_ABS_|||code:1\n@@ -82,7 +82,7 @@ test_expect_success 'perf stream, error event' '\n \tperl \"$TEST_DIRECTORY/t0211/scrub_perf.perl\" actual &&\n \tcat >expect <<-EOF &&\n \t\td0|main|version|||||$V\n-\t\td0|main|start|||||_EXE_ trace2 003error '\\''hello world'\\'' '\\''this is a test'\\''\n+\t\td0|main|start||_T_ABS_|||_EXE_ trace2 003error '\\''hello world'\\'' '\\''this is a test'\\''\n \t\td0|main|cmd_name|||||trace2 (trace2)\n \t\td0|main|error|||||hello world\n \t\td0|main|error|||||this is a test\n@@ -128,15 +128,15 @@ test_expect_success 'perf stream, child processes' '\n \tperl \"$TEST_DIRECTORY/t0211/scrub_perf.perl\" actual &&\n \tcat >expect <<-EOF &&\n \t\td0|main|version|||||$V\n-\t\td0|main|start|||||_EXE_ trace2 004child test-tool trace2 004child test-tool trace2 001return 0\n+\t\td0|main|start||_T_ABS_|||_EXE_ trace2 004child test-tool trace2 004child test-tool trace2 001return 0\n \t\td0|main|cmd_name|||||trace2 (trace2)\n \t\td0|main|child_start||_T_ABS_|||[ch0] class:? argv: test-tool trace2 004child test-tool trace2 001return 0\n \t\td1|main|version|||||$V\n-\t\td1|main|start|||||_EXE_ trace2 004child test-tool trace2 001return 0\n+\t\td1|main|start||_T_ABS_|||_EXE_ trace2 004child test-tool trace2 001return 0\n \t\td1|main|cmd_name|||||trace2 (trace2/trace2)\n \t\td1|main|child_start||_T_ABS_|||[ch0] class:? argv: test-tool trace2 001return 0\n \t\td2|main|version|||||$V\n-\t\td2|main|start|||||_EXE_ trace2 001return 0\n+\t\td2|main|start||_T_ABS_|||_EXE_ trace2 001return 0\n \t\td2|main|cmd_name|||||trace2 (trace2/trace2/trace2)\n \t\td2|main|exit||_T_ABS_|||code:0\n \t\td2|main|atexit||_T_ABS_|||code:0\ndiff --git a/trace2.c b/trace2.c\nindex 6dd51e6aa5..1c180062dd 100644\n--- a/trace2.c\n+++ b/trace2.c\n@@ -182,13 +182,19 @@ void trace2_cmd_start_fl(const char *file, int line, const char **argv)\n {\n \tstruct tr2_tgt *tgt_j;\n \tint j;\n+\tuint64_t us_now;\n+\tuint64_t us_elapsed_absolute;\n \n \tif (!trace2_enabled)\n \t\treturn;\n \n+\tus_now = getnanotime() / 1000;\n+\tus_elapsed_absolute = tr2tls_absolute_elapsed(us_now);\n+\n \tfor_each_wanted_builtin (j, tgt_j)\n \t\tif (tgt_j->pfn_start_fl)\n-\t\t\ttgt_j->pfn_start_fl(file, line, argv);\n+\t\t\ttgt_j->pfn_start_fl(file, line, us_elapsed_absolute,\n+\t\t\t\t\t argv);\n }\n \n int trace2_cmd_exit_fl(const char *file, int line, int code)\ndiff --git a/trace2/tr2_tgt.h b/trace2/tr2_tgt.h\nindex 297bb8ffbe..7b90469212 100644\n--- a/trace2/tr2_tgt.h\n+++ b/trace2/tr2_tgt.h\n@@ -15,6 +15,7 @@ typedef void(tr2_tgt_term_t)(void);\n typedef void(tr2_tgt_evt_version_fl_t)(const char *file, int line);\n \n typedef void(tr2_tgt_evt_start_fl_t)(const char *file, int line,\n+\t\t\t\t uint64_t us_elapsed_absolute,\n \t\t\t\t const char **argv);\n typedef void(tr2_tgt_evt_exit_fl_t)(const char *file, int line,\n \t\t\t\t uint64_t us_elapsed_absolute, int code);\ndiff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c\nindex 107cb5317d..89a4d3ae9a 100644\n--- a/trace2/tr2_tgt_event.c\n+++ b/trace2/tr2_tgt_event.c\n@@ -122,13 +122,16 @@ static void fn_version_fl(const char *file, int line)\n \tjw_release(&jw);\n }\n \n-static void fn_start_fl(const char *file, int line, const char **argv)\n+static void fn_start_fl(const char *file, int line,\n+\t\t\tuint64_t us_elapsed_absolute, const char **argv)\n {\n \tconst char *event_name = \"start\";\n \tstruct json_writer jw = JSON_WRITER_INIT;\n+\tdouble t_abs = (double)us_elapsed_absolute / 1000000.0;\n \n \tjw_object_begin(&jw, 0);\n \tevent_fmt_prepare(event_name, file, line, NULL, &jw);\n+\tjw_object_double(&jw, \"t_abs\", 6, t_abs);\n \tjw_object_inline_begin_array(&jw, \"argv\");\n \tjw_array_argv(&jw, argv);\n \tjw_end(&jw);\ndiff --git a/trace2/tr2_tgt_normal.c b/trace2/tr2_tgt_normal.c\nindex 547183d5b6..57f3e18f5b 100644\n--- a/trace2/tr2_tgt_normal.c\n+++ b/trace2/tr2_tgt_normal.c\n@@ -81,7 +81,8 @@ static void fn_version_fl(const char *file, int line)\n \tstrbuf_release(&buf_payload);\n }\n \n-static void fn_start_fl(const char *file, int line, const char **argv)\n+static void fn_start_fl(const char *file, int line,\n+\t\t\tuint64_t us_elapsed_absolute, const char **argv)\n {\n \tstruct strbuf buf_payload = STRBUF_INIT;\n \ndiff --git a/trace2/tr2_tgt_perf.c b/trace2/tr2_tgt_perf.c\nindex f0746fcf86..9c3b4d8a0f 100644\n--- a/trace2/tr2_tgt_perf.c\n+++ b/trace2/tr2_tgt_perf.c\n@@ -159,15 +159,16 @@ static void fn_version_fl(const char *file, int line)\n \tstrbuf_release(&buf_payload);\n }\n \n-static void fn_start_fl(const char *file, int line, const char **argv)\n+static void fn_start_fl(const char *file, int line,\n+\t\t\tuint64_t us_elapsed_absolute, const char **argv)\n {\n \tconst char *event_name = \"start\";\n \tstruct strbuf buf_payload = STRBUF_INIT;\n \n \tsq_quote_argv_pretty(&buf_payload, argv);\n \n-\tperf_io_write_fl(file, line, event_name, NULL, NULL, NULL, NULL,\n-\t\t\t &buf_payload);\n+\tperf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,\n+\t\t\t NULL, NULL, &buf_payload);\n \tstrbuf_release(&buf_payload);\n }\n \n-- \ngitgitgadget\n\n"},{"id":"372617","messageId":"d4023acde7172089615ea5abd4e91ef90c1791a7.1553779851.git.gitgitgadget@gmail.com","threadId":"50834","inReplyTo":"pull.169.git.gitgitgadget@gmail.com","subject":"[PATCH 3/4] trace2: find exec-dir before trace2 initialization","fromName":"Jeff Hostetler via GitGitGadget","fromEmail":"gitgitgadget@gmail.com","sentAt":"2019-03-28T13:31:02Z","receivedAt":"2019-03-28T13:31:06Z","isPatch":true,"sender":{"key":"git@jeffhostetler.com","avatar":null},"body":"From: Jeff Hostetler \n\nTeach Git to resolve the executable directory before initializing\nTrace2. This allows the system configuration directory to be\ndiscovered earlier (because it is sometimes relative to the prefix\nor runtime-prefix).\n\nThis will be used by the next commit to allow trace2 settings to\nbe loaded from the system config.\n\nSigned-off-by: Jeff Hostetler \n---\n common-main.c | 4 ++--\n 1 file changed, 2 insertions(+), 2 deletions(-)\n\ndiff --git a/common-main.c b/common-main.c\nindex 6137af0e63..299ca62a72 100644\n--- a/common-main.c\n+++ b/common-main.c\n@@ -37,12 +37,12 @@ int main(int argc, const char **argv)\n \tsanitize_stdfds();\n \trestore_sigpipe_to_default();\n \n+\tgit_resolve_executable_dir(argv[0]);\n+\n \ttrace2_initialize();\n \ttrace2_cmd_start(argv);\n \ttrace2_collect_process_info();\n \n-\tgit_resolve_executable_dir(argv[0]);\n-\n \tgit_setup_gettext();\n \n \tinitialize_the_repository();\n-- \ngitgitgadget\n\n"},{"id":"372618","messageId":"7e0d4e20fbb3abbc787bc216d2c4bd8c18860aed.1553779851.git.gitgitgadget@gmail.com","threadId":"50834","inReplyTo":"pull.169.git.gitgitgadget@gmail.com","subject":"[PATCH 4/4] trace2: use system config for default trace2 settings","fromName":"Jeff Hostetler via GitGitGadget","fromEmail":"gitgitgadget@gmail.com","sentAt":"2019-03-28T13:31:04Z","receivedAt":"2019-03-28T13:31:10Z","isPatch":true,"sender":{"key":"git@jeffhostetler.com","avatar":null},"body":"From: Jeff Hostetler \n\nTeach git to read the system config (usually \"/etc/gitconfig\") for\ndefault Trace2 settings. This allows system-wide Trace2 settings to\nbe installed and inherited to make it easier to manage a collection of\nsystems.\n\nThe original GIT_TR2* environment variables are loaded afterwards and\ncan be used to override the system settings.\n\nOnly the system config file is used. Trace2 config values are ignored\nin local, global, and other config files. Likewise, the \"-c\" command\nline arguments are ignored for Trace2 values. These limits are for\nperformance reasons.\n\n(1) For users not using Trace2, there should be minimal overhead to\ndetect that Trace2 is not enabled. In particular, Trace2 should not\nallocate lots of otherwise unused data strucutres.\n\n(2) For accurate performance measurements, Trace2 should be initialized\nas early in the git process as possible, and before most of the normal\ngit process initialization (which involves discovering the .git directory\nand reading a hierarchy of config files).\n\nAdded the GIT_TEST_TR2_SYSTEM_CONFIG environment variable for testing\npurposes to specify the pathname of a fake \"system\" config or disable\nuse of the system config.\n\nSigned-off-by: Jeff Hostetler \n---\n Documentation/technical/api-trace2.txt | 31 ++++++\n Makefile | 1 +\n t/t0210-trace2-normal.sh | 41 +++++++-\n t/t0211-trace2-perf.sh | 41 +++++++-\n t/t0212-trace2-event.sh | 52 +++++++++-\n trace2.c | 4 +\n trace2.h | 7 +-\n trace2/tr2_cfg.c | 7 +-\n trace2/tr2_dst.c | 24 ++---\n trace2/tr2_dst.h | 3 +-\n trace2/tr2_sysenv.c | 125 +++++++++++++++++++++++++\n trace2/tr2_sysenv.h | 36 +++++++\n trace2/tr2_tgt_event.c | 19 ++--\n trace2/tr2_tgt_normal.c | 10 +-\n trace2/tr2_tgt_perf.c | 10 +-\n 15 files changed, 356 insertions(+), 55 deletions(-)\n create mode 100644 trace2/tr2_sysenv.c\n create mode 100644 trace2/tr2_sysenv.h\n\ndiff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt\nindex baaa1153bb..13ca595c69 100644\n--- a/Documentation/technical/api-trace2.txt\n+++ b/Documentation/technical/api-trace2.txt\n@@ -117,6 +117,37 @@ values are recognized.\n Socket type can be either `stream` or `dgram`. If the socket type is\n omitted, Git will try both.\n \n+== Trace2 Settings in System Config\n+\n+Trace2 also reads configuration information from the system config.\n+This is intended to help adminstrators to gather system-wide Git\n+performance data.\n+\n+Trace2 only reads the system configuration, it does not read global,\n+local, worktree, or `-c` config settings.\n+\n+Trace2 will try to load the following system configuration settings\n+and then read the corresponding environment variables at startup.\n+\n+....\n+---------------------------------------------------\n+trace2.normalTarget GIT_TR2\n+trace2.normalBrief GIT_TR2_BRIEF\n+\n+trace2.perfTarget GIT_TR2_PERF\n+trace2.perfBrief GIT_TR2_PERF_BRIEF\n+\n+trace2.eventTarget GIT_TR2_EVENT\n+trace2.eventBrief GIT_TR2_EVENT_BRIEF\n+trace2.eventNesting GIT_TR2_EVENT_NESTING\n+\n+trace2.configParams GIT_TR2_CONFIG_PARAMS\n+\n+trace2.destinationDebug GIT_TR2_DST_DEBUG\n+---------------------------------------------------\n+....\n+\n+\n == Trace2 API\n \n All public Trace2 functions and macros are defined in `trace2.h` and\ndiff --git a/Makefile b/Makefile\nindex 3e03290d8f..9ddfa3dfe7 100644\n--- a/Makefile\n+++ b/Makefile\n@@ -1005,6 +1005,7 @@ LIB_OBJS += trace2/tr2_cfg.o\n LIB_OBJS += trace2/tr2_cmd_name.o\n LIB_OBJS += trace2/tr2_dst.o\n LIB_OBJS += trace2/tr2_sid.o\n+LIB_OBJS += trace2/tr2_sysenv.o\n LIB_OBJS += trace2/tr2_tbuf.o\n LIB_OBJS += trace2/tr2_tgt_event.o\n LIB_OBJS += trace2/tr2_tgt_normal.o\ndiff --git a/t/t0210-trace2-normal.sh b/t/t0210-trace2-normal.sh\nindex 03a0aedb1d..5d4c04ed30 100755\n--- a/t/t0210-trace2-normal.sh\n+++ b/t/t0210-trace2-normal.sh\n@@ -1,5 +1,14 @@\n #!/bin/sh\n \n+# Disable loading of Trace2 settings from the system config\n+# (usually \"/etc/gitconfig\") to eliminate system dependencies.\n+GIT_TEST_TR2_SYSTEM_CONFIG=0 && export GIT_TEST_TR2_SYSTEM_CONFIG\n+\n+# Turn off any inherited trace2 settings for this test.\n+unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT\n+unset GIT_TR2_BRIEF\n+unset GIT_TR2_CONFIG_PARAMS\n+\n test_description='test trace2 facility (normal target)'\n . ./test-lib.sh\n \n@@ -15,11 +24,6 @@ PATH=\"$TTDIR:$PATH\" && export PATH\n # Warning: So you may see extra lines in artifact files when\n # Warning: interactively debugging.\n \n-# Turn off any inherited trace2 settings for this test.\n-unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT\n-unset GIT_TR2_BRIEF\n-unset GIT_TR2_CONFIG_PARAMS\n-\n V=$(git version | sed -e 's/^git version //') && export V\n \n # There are multiple trace2 targets: normal, perf, and event.\n@@ -132,4 +136,31 @@ test_expect_success 'normal stream, error event' '\n \ttest_cmp expect actual\n '\n \n+# Now test using system config by using a mocked up config file\n+# rather than inheriting \"/etc/gitconfig\". Here we do not use\n+# GIT_TR2* environment variables.\n+\n+unset GIT_TR2_BRIEF\n+\n+MOCK=./mock_system_config\n+\n+test_expect_success 'setup mocked /etc/gitconfig' '\n+\tgit config --file $MOCK trace2.normalTarget \"$(pwd)/trace.normal\" &&\n+\tgit config --file $MOCK trace2.normalBrief 1\n+'\n+\n+test_expect_success 'using mock, normal stream, return code 0' '\n+\ttest_when_finished \"rm trace.normal actual expect\" &&\n+\tGIT_TEST_TR2_SYSTEM_CONFIG=\"$MOCK\" test-tool trace2 001return 0 &&\n+\tperl \"$TEST_DIRECTORY/t0210/scrub_normal.perl\" actual &&\n+\tcat >expect <<-EOF &&\n+\t\tversion $V\n+\t\tstart _EXE_ trace2 001return 0\n+\t\tcmd_name trace2 (trace2)\n+\t\texit elapsed:_TIME_ code:0\n+\t\tatexit elapsed:_TIME_ code:0\n+\tEOF\n+\ttest_cmp expect actual\n+'\n+\n test_done\ndiff --git a/t/t0211-trace2-perf.sh b/t/t0211-trace2-perf.sh\nindex c9694b29f7..abe35b2186 100755\n--- a/t/t0211-trace2-perf.sh\n+++ b/t/t0211-trace2-perf.sh\n@@ -1,5 +1,14 @@\n #!/bin/sh\n \n+# Disable loading of Trace2 settings from the system config\n+# (usually \"/etc/gitconfig\") to eliminate system dependencies.\n+GIT_TEST_TR2_SYSTEM_CONFIG=0 && export GIT_TEST_TR2_SYSTEM_CONFIG\n+\n+# Turn off any inherited trace2 settings for this test.\n+unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT\n+unset GIT_TR2_PERF_BRIEF\n+unset GIT_TR2_CONFIG_PARAMS\n+\n test_description='test trace2 facility (perf target)'\n . ./test-lib.sh\n \n@@ -15,11 +24,6 @@ PATH=\"$TTDIR:$PATH\" && export PATH\n # Warning: So you may see extra lines in artifact files when\n # Warning: interactively debugging.\n \n-# Turn off any inherited trace2 settings for this test.\n-unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT\n-unset GIT_TR2_PERF_BRIEF\n-unset GIT_TR2_CONFIG_PARAMS\n-\n V=$(git version | sed -e 's/^git version //') && export V\n \n # There are multiple trace2 targets: normal, perf, and event.\n@@ -150,4 +154,31 @@ test_expect_success 'perf stream, child processes' '\n \ttest_cmp expect actual\n '\n \n+# Now test using system config by using a mocked up config file\n+# rather than inheriting \"/etc/gitconfig\". Here we do not use\n+# GIT_TR2* environment variables.\n+\n+unset GIT_TR2_PERF_BRIEF\n+\n+MOCK=./mock_system_config\n+\n+test_expect_success 'setup mocked /etc/gitconfig' '\n+\tgit config --file $MOCK trace2.perfTarget \"$(pwd)/trace.perf\" &&\n+\tgit config --file $MOCK trace2.perfBrief 1\n+'\n+\n+test_expect_success 'using mock, perf stream, return code 0' '\n+\ttest_when_finished \"rm trace.perf actual expect\" &&\n+\tGIT_TEST_TR2_SYSTEM_CONFIG=\"$MOCK\" test-tool trace2 001return 0 &&\n+\tperl \"$TEST_DIRECTORY/t0211/scrub_perf.perl\" actual &&\n+\tcat >expect <<-EOF &&\n+\t\td0|main|version|||||$V\n+\t\td0|main|start||_T_ABS_|||_EXE_ trace2 001return 0\n+\t\td0|main|cmd_name|||||trace2 (trace2)\n+\t\td0|main|exit||_T_ABS_|||code:0\n+\t\td0|main|atexit||_T_ABS_|||code:0\n+\tEOF\n+\ttest_cmp expect actual\n+'\n+\n test_done\ndiff --git a/t/t0212-trace2-event.sh b/t/t0212-trace2-event.sh\nindex 028b6c5671..c535496261 100755\n--- a/t/t0212-trace2-event.sh\n+++ b/t/t0212-trace2-event.sh\n@@ -1,5 +1,14 @@\n #!/bin/sh\n \n+# Disable loading of Trace2 settings from the system config\n+# (usually \"/etc/gitconfig\") to eliminate system dependencies.\n+GIT_TEST_TR2_SYSTEM_CONFIG=0 && export GIT_TEST_TR2_SYSTEM_CONFIG\n+\n+# Turn off any inherited trace2 settings for this test.\n+unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT\n+unset GIT_TR2_BARE\n+unset GIT_TR2_CONFIG_PARAMS\n+\n test_description='test trace2 facility'\n . ./test-lib.sh\n \n@@ -17,11 +26,6 @@ PATH=\"$TTDIR:$PATH\" && export PATH\n # Warning: So you may see extra lines in artifact files when\n # Warning: interactively debugging.\n \n-# Turn off any inherited trace2 settings for this test.\n-unset GIT_TR2 GIT_TR2_PERF GIT_TR2_EVENT\n-unset GIT_TR2_BARE\n-unset GIT_TR2_CONFIG_PARAMS\n-\n V=$(git version | sed -e 's/^git version //') && export V\n \n # There are multiple trace2 targets: normal, perf, and event.\n@@ -233,4 +237,42 @@ test_expect_success JSON_PP 'basic trace2_data' '\n \ttest_cmp expect actual\n '\n \n+# Now test using system config by using a mocked up config file\n+# rather than inheriting \"/etc/gitconfig\". Here we do not use\n+# GIT_TR2* environment variables.\n+\n+MOCK=./mock_system_config\n+\n+test_expect_success 'setup mocked /etc/gitconfig' '\n+\tgit config --file $MOCK trace2.eventTarget \"$(pwd)/trace.event\"\n+'\n+\n+test_expect_success JSON_PP 'using mock, event stream, error event' '\n+\ttest_when_finished \"rm trace.event actual expect\" &&\n+\tGIT_TEST_TR2_SYSTEM_CONFIG=\"$MOCK\" test-tool trace2 003error \"hello world\" \"this is a test\" &&\n+\tperl \"$TEST_DIRECTORY/t0212/parse_events.perl\" actual &&\n+\tsed -e \"s/^|//\" >expect <<-EOF &&\n+\t|VAR1 = {\n+\t| \"_SID0_\":{\n+\t| \"argv\":[\n+\t| \"_EXE_\",\n+\t| \"trace2\",\n+\t| \"003error\",\n+\t| \"hello world\",\n+\t| \"this is a test\"\n+\t| ],\n+\t| \"errors\":[\n+\t| \"%s\",\n+\t| \"%s\"\n+\t| ],\n+\t| \"exit_code\":0,\n+\t| \"hierarchy\":\"trace2\",\n+\t| \"name\":\"trace2\",\n+\t| \"version\":\"$V\"\n+\t| }\n+\t|};\n+\tEOF\n+\ttest_cmp expect actual\n+'\n+\n test_done\ndiff --git a/trace2.c b/trace2.c\nindex 1c180062dd..490b3f071e 100644\n--- a/trace2.c\n+++ b/trace2.c\n@@ -10,6 +10,7 @@\n #include \"trace2/tr2_cmd_name.h\"\n #include \"trace2/tr2_dst.h\"\n #include \"trace2/tr2_sid.h\"\n+#include \"trace2/tr2_sysenv.h\"\n #include \"trace2/tr2_tgt.h\"\n #include \"trace2/tr2_tls.h\"\n \n@@ -120,6 +121,7 @@ static void tr2main_atexit_handler(void)\n \ttr2_sid_release();\n \ttr2_cmd_name_release();\n \ttr2_cfg_free_patterns();\n+\ttr2_sysenv_release();\n \n \ttrace2_enabled = 0;\n }\n@@ -155,6 +157,8 @@ void trace2_initialize_fl(const char *file, int line)\n \tif (trace2_enabled)\n \t\treturn;\n \n+\ttr2_sysenv_load();\n+\n \tif (!tr2_tgt_want_builtins())\n \t\treturn;\n \ttrace2_enabled = 1;\ndiff --git a/trace2.h b/trace2.h\nindex 8f89e70c44..cda8349058 100644\n--- a/trace2.h\n+++ b/trace2.h\n@@ -38,7 +38,8 @@ void trace2_initialize_clock(void);\n \n /*\n * Initialize TRACE2 tracing facility if any of the builtin TRACE2\n- * targets are enabled in the environment. Emits a 'version' event.\n+ * targets are enabled in the system config or the environment.\n+ * Emits a 'version' event.\n *\n * Cleanup/Termination is handled automatically by a registered\n * atexit() routine.\n@@ -125,8 +126,8 @@ void trace2_cmd_alias_fl(const char *file, int line, const char *alias,\n * Emit one or more 'def_param' events for \"interesting\" configuration\n * settings.\n *\n- * The environment variable \"GIT_TR2_CONFIG_PARAMS\" can be set to a\n- * list of patterns considered important. For example:\n+ * Use the TR2_SYSENV_CFG_PARAM setting to register a list of patterns\n+ * configured important. For example:\n *\n * GIT_TR2_CONFIG_PARAMS=\"core.*,remote.*.url\"\n *\ndiff --git a/trace2/tr2_cfg.c b/trace2/tr2_cfg.c\nindex b329921ac5..caa7f06948 100644\n--- a/trace2/tr2_cfg.c\n+++ b/trace2/tr2_cfg.c\n@@ -1,8 +1,7 @@\n #include \"cache.h\"\n #include \"config.h\"\n-#include \"tr2_cfg.h\"\n-\n-#define TR2_ENVVAR_CFG_PARAM \"GIT_TR2_CONFIG_PARAMS\"\n+#include \"trace2/tr2_cfg.h\"\n+#include \"trace2/tr2_sysenv.h\"\n \n static struct strbuf **tr2_cfg_patterns;\n static int tr2_cfg_count_patterns;\n@@ -21,7 +20,7 @@ static int tr2_cfg_load_patterns(void)\n \t\treturn tr2_cfg_count_patterns;\n \ttr2_cfg_loaded = 1;\n \n-\tenvvar = getenv(TR2_ENVVAR_CFG_PARAM);\n+\tenvvar = tr2_sysenv_get(TR2_SYSENV_CFG_PARAM);\n \tif (!envvar || !*envvar)\n \t\treturn tr2_cfg_count_patterns;\n \ndiff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c\nindex fd490a43ad..575cd69aa9 100644\n--- a/trace2/tr2_dst.c\n+++ b/trace2/tr2_dst.c\n@@ -1,5 +1,6 @@\n #include \"cache.h\"\n #include \"trace2/tr2_dst.h\"\n+#include \"trace2/tr2_sysenv.h\"\n \n /*\n * If a Trace2 target cannot be opened for writing, we should issue a\n@@ -7,17 +8,13 @@\n * or socket and beyond the user's control -- especially since every\n * git command (and sub-command) will print the message. So we silently\n * eat these warnings and just discard the trace data.\n- *\n- * Enable the following environment variable to see these warnings.\n */\n-#define TR2_ENVVAR_DST_DEBUG \"GIT_TR2_DST_DEBUG\"\n-\n static int tr2_dst_want_warning(void)\n {\n \tstatic int tr2env_dst_debug = -1;\n \n \tif (tr2env_dst_debug == -1) {\n-\t\tconst char *env_value = getenv(TR2_ENVVAR_DST_DEBUG);\n+\t\tconst char *env_value = tr2_sysenv_get(TR2_SYSENV_DST_DEBUG);\n \t\tif (!env_value || !*env_value)\n \t\t\ttr2env_dst_debug = 0;\n \t\telse\n@@ -42,7 +39,9 @@ static int tr2_dst_try_path(struct tr2_dst *dst, const char *tgt_value)\n \tif (fd == -1) {\n \t\tif (tr2_dst_want_warning())\n \t\t\twarning(\"trace2: could not open '%s' for '%s' tracing: %s\",\n-\t\t\t\ttgt_value, dst->env_var_name, strerror(errno));\n+\t\t\t\ttgt_value,\n+\t\t\t\ttr2_sysenv_display_name(dst->sysenv_var),\n+\t\t\t\tstrerror(errno));\n \n \t\ttr2_dst_trace_disable(dst);\n \t\treturn 0;\n@@ -116,7 +115,7 @@ static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,\n \tif (!path || !*path) {\n \t\tif (tr2_dst_want_warning())\n \t\t\twarning(\"trace2: invalid AF_UNIX value '%s' for '%s' tracing\",\n-\t\t\t\ttgt_value, dst->env_var_name);\n+\t\t\t\ttgt_value, tr2_sysenv_display_name(dst->sysenv_var));\n \n \t\ttr2_dst_trace_disable(dst);\n \t\treturn 0;\n@@ -126,7 +125,7 @@ static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,\n \t strlen(path) >= sizeof(((struct sockaddr_un *)0)->sun_path)) {\n \t\tif (tr2_dst_want_warning())\n \t\t\twarning(\"trace2: invalid AF_UNIX path '%s' for '%s' tracing\",\n-\t\t\t\tpath, dst->env_var_name);\n+\t\t\t\tpath, tr2_sysenv_display_name(dst->sysenv_var));\n \n \t\ttr2_dst_trace_disable(dst);\n \t\treturn 0;\n@@ -148,7 +147,7 @@ static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,\n error:\n \tif (tr2_dst_want_warning())\n \t\twarning(\"trace2: could not connect to socket '%s' for '%s' tracing: %s\",\n-\t\t\tpath, dst->env_var_name, strerror(e));\n+\t\t\tpath, tr2_sysenv_display_name(dst->sysenv_var), strerror(e));\n \n \ttr2_dst_trace_disable(dst);\n \treturn 0;\n@@ -168,7 +167,7 @@ static void tr2_dst_malformed_warning(struct tr2_dst *dst,\n \tstruct strbuf buf = STRBUF_INIT;\n \n \tstrbuf_addf(&buf, \"trace2: unknown value for '%s': '%s'\",\n-\t\t dst->env_var_name, tgt_value);\n+\t\t tr2_sysenv_display_name(dst->sysenv_var), tgt_value);\n \twarning(\"%s\", buf.buf);\n \n \tstrbuf_release(&buf);\n@@ -184,7 +183,7 @@ int tr2_dst_get_trace_fd(struct tr2_dst *dst)\n \n \tdst->initialized = 1;\n \n-\ttgt_value = getenv(dst->env_var_name);\n+\ttgt_value = tr2_sysenv_get(dst->sysenv_var);\n \n \tif (!tgt_value || !strcmp(tgt_value, \"\") || !strcmp(tgt_value, \"0\") ||\n \t !strcasecmp(tgt_value, \"false\")) {\n@@ -246,7 +245,8 @@ void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line)\n \t\treturn;\n \n \tif (tr2_dst_want_warning())\n-\t\twarning(\"unable to write trace to '%s': %s\", dst->env_var_name,\n+\t\twarning(\"unable to write trace to '%s': %s\",\n+\t\t\ttr2_sysenv_display_name(dst->sysenv_var),\n \t\t\tstrerror(errno));\n \ttr2_dst_trace_disable(dst);\n }\ndiff --git a/trace2/tr2_dst.h b/trace2/tr2_dst.h\nindex 9a64f05b02..3adf3bac13 100644\n--- a/trace2/tr2_dst.h\n+++ b/trace2/tr2_dst.h\n@@ -2,9 +2,10 @@\n #define TR2_DST_H\n \n struct strbuf;\n+#include \"trace2/tr2_sysenv.h\"\n \n struct tr2_dst {\n-\tconst char *const env_var_name;\n+\tenum tr2_sysenv_variable sysenv_var;\n \tint fd;\n \tunsigned int initialized : 1;\n \tunsigned int need_close : 1;\ndiff --git a/trace2/tr2_sysenv.c b/trace2/tr2_sysenv.c\nnew file mode 100644\nindex 0000000000..656613e371\n--- /dev/null\n+++ b/trace2/tr2_sysenv.c\n@@ -0,0 +1,125 @@\n+#include \"cache.h\"\n+#include \"config.h\"\n+#include \"dir.h\"\n+#include \"tr2_sysenv.h\"\n+\n+/*\n+ * Each entry represents a trace2 setting.\n+ * See Documentation/technical/api-trace2.txt\n+ */\n+struct tr2_sysenv_entry {\n+\tconst char *env_var_name;\n+\tconst char *git_config_name;\n+\n+\tchar *value;\n+\tunsigned int getenv_called : 1;\n+};\n+\n+/*\n+ * This table must match \"enum tr2_sysenv_variable\" in tr2_sysenv.h.\n+ * These strings are constant and must match the published names as\n+ * described in the documentation.\n+ *\n+ * We do not define entries for the GIT_TR2_PARENT_* environment\n+ * variables because they are transient and used to pass information\n+ * from parent to child git processes, rather than settings.\n+ */\n+/* clang-format off */\n+static struct tr2_sysenv_entry tr2_sysenv_settings[] = {\n+\t{ \"GIT_TR2_CONFIG_PARAMS\", \"trace2.configparams\" },\n+\n+\t{ \"GIT_TR2_DST_DEBUG\", \"trace2.destinationdebug\" },\n+\n+\t{ \"GIT_TR2\", \"trace2.normaltarget\" },\n+\t{ \"GIT_TR2_BRIEF\", \"trace2.normalbrief\" },\n+\n+\t{ \"GIT_TR2_EVENT\", \"trace2.eventtarget\" },\n+\t{ \"GIT_TR2_EVENT_BRIEF\", \"trace2.eventbrief\" },\n+\t{ \"GIT_TR2_EVENT_NESTING\", \"trace2.eventnesting\" },\n+\n+\t{ \"GIT_TR2_PERF\", \"trace2.perftarget\" },\n+\t{ \"GIT_TR2_PERF_BRIEF\", \"trace2.perfbrief\" },\n+};\n+/* clang-format on */\n+\n+static int tr2_sysenv_cb(const char *key, const char *value, void *d)\n+{\n+\tint k;\n+\n+\tfor (k = 0; k < ARRAY_SIZE(tr2_sysenv_settings); k++) {\n+\t\tif (!strcmp(key, tr2_sysenv_settings[k].git_config_name)) {\n+\t\t\tfree(tr2_sysenv_settings[k].value);\n+\t\t\ttr2_sysenv_settings[k].value = xstrdup(value);\n+\t\t\treturn 0;\n+\t\t}\n+\t}\n+\n+\treturn 0;\n+}\n+\n+/*\n+ * Load Trace2 settings from the system config (usually \"/etc/gitconfig\"\n+ * unless we were built with a runtime-prefix). These are intended to\n+ * define the default values for Trace2 as requested by the administrator.\n+ */\n+void tr2_sysenv_load(void)\n+{\n+\tconst char *system_config_pathname;\n+\tconst char *test_pathname;\n+\n+\tsystem_config_pathname = git_etc_gitconfig();\n+\n+\ttest_pathname = getenv(\"GIT_TEST_TR2_SYSTEM_CONFIG\");\n+\tif (test_pathname) {\n+\t\tif (!*test_pathname || !strcmp(test_pathname, \"0\"))\n+\t\t\treturn; /* disable use of system config */\n+\n+\t\t/* mock it with given test file */\n+\t\tsystem_config_pathname = test_pathname;\n+\t}\n+\n+\tif (file_exists(system_config_pathname))\n+\t\tgit_config_from_file(tr2_sysenv_cb, system_config_pathname,\n+\t\t\t\t NULL);\n+}\n+\n+/*\n+ * Return the value for the requested setting. Start with the /etc/gitconfig\n+ * value and allow the corresponding environment variable to override it.\n+ */\n+const char *tr2_sysenv_get(enum tr2_sysenv_variable var)\n+{\n+\tif (var >= TR2_SYSENV_MUST_BE_LAST)\n+\t\tBUG(\"tr2_sysenv_get invalid var '%d'\", var);\n+\n+\tif (!tr2_sysenv_settings[var].getenv_called) {\n+\t\tconst char *v = getenv(tr2_sysenv_settings[var].env_var_name);\n+\t\tif (v && *v) {\n+\t\t\tfree(tr2_sysenv_settings[var].value);\n+\t\t\ttr2_sysenv_settings[var].value = xstrdup(v);\n+\t\t}\n+\t\ttr2_sysenv_settings[var].getenv_called = 1;\n+\t}\n+\n+\treturn tr2_sysenv_settings[var].value;\n+}\n+\n+/*\n+ * Return a friendly name for this setting that is suitable for printing\n+ * in an error messages.\n+ */\n+const char *tr2_sysenv_display_name(enum tr2_sysenv_variable var)\n+{\n+\tif (var >= TR2_SYSENV_MUST_BE_LAST)\n+\t\tBUG(\"tr2_sysenv_get invalid var '%d'\", var);\n+\n+\treturn tr2_sysenv_settings[var].env_var_name;\n+}\n+\n+void tr2_sysenv_release(void)\n+{\n+\tint k;\n+\n+\tfor (k = 0; k < ARRAY_SIZE(tr2_sysenv_settings); k++)\n+\t\tfree(tr2_sysenv_settings[k].value);\n+}\ndiff --git a/trace2/tr2_sysenv.h b/trace2/tr2_sysenv.h\nnew file mode 100644\nindex 0000000000..369b20bd87\n--- /dev/null\n+++ b/trace2/tr2_sysenv.h\n@@ -0,0 +1,36 @@\n+#ifndef TR2_SYSENV_H\n+#define TR2_SYSENV_H\n+\n+/*\n+ * The Trace2 settings that can be loaded from /etc/gitconfig\n+ * and/or user environment variables.\n+ *\n+ * Note that this set does not contain any of the transient\n+ * environment variables used to pass information from parent\n+ * to child git processes, such \"GIT_TR2_PARENT_SID\".\n+ */\n+enum tr2_sysenv_variable {\n+\tTR2_SYSENV_CFG_PARAM = 0,\n+\n+\tTR2_SYSENV_DST_DEBUG,\n+\n+\tTR2_SYSENV_NORMAL,\n+\tTR2_SYSENV_NORMAL_BRIEF,\n+\n+\tTR2_SYSENV_EVENT,\n+\tTR2_SYSENV_EVENT_BRIEF,\n+\tTR2_SYSENV_EVENT_NESTING,\n+\n+\tTR2_SYSENV_PERF,\n+\tTR2_SYSENV_PERF_BRIEF,\n+\n+\tTR2_SYSENV_MUST_BE_LAST\n+};\n+\n+void tr2_sysenv_load(void);\n+\n+const char *tr2_sysenv_get(enum tr2_sysenv_variable);\n+const char *tr2_sysenv_display_name(enum tr2_sysenv_variable var);\n+void tr2_sysenv_release(void);\n+\n+#endif /* TR2_SYSENV_H */\ndiff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c\nindex 89a4d3ae9a..bb6e323953 100644\n--- a/trace2/tr2_tgt_event.c\n+++ b/trace2/tr2_tgt_event.c\n@@ -6,10 +6,11 @@\n #include \"trace2/tr2_dst.h\"\n #include \"trace2/tr2_tbuf.h\"\n #include \"trace2/tr2_sid.h\"\n+#include \"trace2/tr2_sysenv.h\"\n #include \"trace2/tr2_tgt.h\"\n #include \"trace2/tr2_tls.h\"\n \n-static struct tr2_dst tr2dst_event = { \"GIT_TR2_EVENT\", 0, 0, 0 };\n+static struct tr2_dst tr2dst_event = { TR2_SYSENV_EVENT, 0, 0, 0 };\n \n /*\n * The version number of the JSON data generated by the EVENT target\n@@ -28,17 +29,15 @@ static struct tr2_dst tr2dst_event = { \"GIT_TR2_EVENT\", 0, 0, 0 };\n * are primarily intended for the performance target during debugging.\n *\n * Some of the outer-most messages, however, may be of interest to the\n- * event target. Set this environment variable to a larger integer for\n- * more detail in the event target.\n+ * event target. Use the TR2_SYSENV_EVENT_NESTING setting to increase\n+ * region details in the event target.\n */\n-#define TR2_ENVVAR_EVENT_NESTING \"GIT_TR2_EVENT_NESTING\"\n static int tr2env_event_nesting_wanted = 2;\n \n /*\n- * Set this environment variable to true to omit the