From: Johannes Schindelin via GitGitGadget Date: Fri, 29 Oct 2021 13:59:13 GMT Subject: [PATCH v3 2/8] test-tool genzeros: generate large amounts of data more efficiently Message-ID: <052197200141c321118b7766f5615a61f951e59f.1635515959.git.gitgitgadget@gmail.com> In-Reply-To: From: Johannes Schindelin In this developer's tests, producing one gigabyte worth of NULs in a busy loop that writes out individual bytes, unbuffered, took ~27sec. Writing chunked 256kB buffers instead only took ~0.6sec This matters because we are about to introduce a pair of test cases that want to be able to produce 5GB of NULs, and we cannot use `/dev/zero` because of the HP NonStop platform's lack of support for that device. Signed-off-by: Johannes Schindelin --- t/helper/test-genzeros.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/t/helper/test-genzeros.c b/t/helper/test-genzeros.c index b1197e91a89..8ca988d6216 100644 --- a/t/helper/test-genzeros.c +++ b/t/helper/test-genzeros.c @@ -3,7 +3,10 @@ int cmd__genzeros(int argc, const char **argv) { + /* static, so that it is NUL-initialized */ + static const char zeros[256 * 1024]; intmax_t count; + ssize_t n; if (argc > 2) { fprintf(stderr, "usage: %s []\n", argv[0]); @@ -12,9 +15,19 @@ int cmd__genzeros(int argc, const char **argv) count = argc > 1 ? strtoimax(argv[1], NULL, 0) : -1; - while (count < 0 || count--) { - if (putchar(0) == EOF) + /* Writing out individual NUL bytes is slow... */ + while (count < 0) + if (write(1, zeros, ARRAY_SIZE(zeros)) < 0) return -1; + + while (count > 0) { + n = write(1, zeros, count < ARRAY_SIZE(zeros) ? + count : ARRAY_SIZE(zeros)); + + if (n < 0) + return -1; + + count -= n; } return 0; -- gitgitgadget