[PATCH] trace2: don't include "fsync" events in all trace2 logs

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Jun 23, 2022, 15:51 UTC
Message-ID: <patch-1.1-df87e515efd-20220623T154943Z-avarab@gmail.com>

Fix the overly verbose trace2 logging added in 9a4987677d3 (trace2: add stats for fsync operations, 2022-03-30) (first released with v2.36.0).

Since that change every single "git" command invocation has included these "data" events, even though we'll only make use of these with core.fsyncMethod=batch, and even then only have non-zero values if we're writing object data to disk. See c0f4752ed2f (core.fsyncmethod: batched disk flushes for loose-objects, 2022-04-04) for that feature.

The result was that e.g. "git version" would previously emit a total
of 6 trace2 events with the GIT_TRACE2_EVENT target (version, start,
cmd_ancestry, cmd_name, exit, atexit), but afterwards would emit
8. We'd emit 2 "data" events before the "exit" event.

The reason we didn't catch this was that the trace2 unit tests added in a15860dca3f (trace2: t/helper/test-trace2, t0210.sh, t0211.sh, t0212.sh, 2019-02-22) would omit any "data" events that weren't the ones it cared about. Before this change to the C code 6/7 of our "t/t0212-trace2-event.sh" tests would fail if this change was applied to "t/t0212/parse_events.perl".

Let's make the trace2 testing more strict, and further append any new events types we don't know about in "t/t0212/parse_events.perl". Since we only invoke the "test-tool trace2" there's no guarantee that we'll catch other overly verbose events in the future, but we'll at least notice if we start emitting new events that are issues every time we log anything with trace2's JSON target.

We exclude the "data_json" event type, we'd otherwise would fail on both "win test" and "win+VS test" CI due to the logging added in 353d3d77f4f (trace2: collect Windows-specific process information, 2019-02-22). It looks like that logging should really be using trace2_cmd_ancestry() instead, which was introduced later in 2f732bf15e6 (tr2: log parent process name, 2021-07-21), but let's leave it for now.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

This is a fix for a v2.36.0 regression/change, so perhaps it's categorically out for v2.37.0, but given how isolated the fix is & how verbose the new trace2 data is perhaps it's worth including anyway.

Passing CI at: https://github.com/avar/git/actions/runs/2548732003

 t/t0212/parse_events.perl | 17 +++++++++++------
 wrapper.c                 |  3 +++
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/t/t0212/parse_events.perl b/t/t0212/parse_events.perl
index b6408560c0c..389cf6f61c4 100644
--- a/t/t0212/parse_events.perl
+++ b/t/t0212/parse_events.perl
@@ -216,12 +216,17 @@
 
     elsif ($event eq 'data') {
 	my $cat = $line->{'category'};
-	if ($cat eq 'test_category') {
-	    
-	    my $key = $line->{'key'};
-	    my $value = $line->{'value'};
-	    $processes->{$sid}->{'data'}->{$cat}->{$key} = $value;
-	}
+	my $key = $line->{'key'};
+	my $value = $line->{'value'};
+	$processes->{$sid}->{'data'}->{$cat}->{$key} = $value;
+    }
+
+    elsif ($event eq 'data_json') {
+	# Ignore due to compat/win32/trace2_win32_process_info.c
+    }
+
+    else {
+	push @{$processes->{$sid}->{$event}} => $line->{value};
     }
 
     # This trace2 target does not emit 'printf' events.
diff --git a/wrapper.c b/wrapper.c
index 1c3c970080b..eebd764131f 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -618,6 +618,9 @@ int git_fsync(int fd, enum fsync_action action)
 
 void trace_git_fsync_stats(void)
 {
+	if (!count_fsync_writeout_only && !count_fsync_hardware_flush)
+		return;
+
 	trace2_data_intmax("fsync", the_repository, "fsync/writeout-only", count_fsync_writeout_only);
 	trace2_data_intmax("fsync", the_repository, "fsync/hardware-flush", count_fsync_hardware_flush);
 }

-- 
2.37.0.rc2.867.gbe8216e3e5c