test-tool genzeros: generate large amounts of data more efficiently
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 <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Johannes Schindelin committed
Nov 2, 2021 at 15:46 UTC
df7000cd910a5f6991f73991b87d838a5d75e2fc
1 file changed
+15
-2
t/helper/test-genzeros.c
+15
-2
@@ -3,7 +3,10 @@
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int cmd__genzeros(int argc, const char **argv)
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{
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+ /* static, so that it is NUL-initialized */
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+ static const char zeros[256 * 1024];
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intmax_t count;
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+ ssize_t n;
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if (argc > 2) {
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fprintf(stderr, "usage: %s [<count>]\n", argv[0]);
@@ -12,9 +15,19 @@ int cmd__genzeros(int argc, const char **argv)
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count = argc > 1 ? strtoimax(argv[1], NULL, 0) : -1;
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- while (count < 0 || count--) {
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- if (putchar(0) == EOF)
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+ /* Writing out individual NUL bytes is slow... */
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+ while (count < 0)
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+ if (write(1, zeros, ARRAY_SIZE(zeros)) < 0)
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return -1;
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+
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+ while (count > 0) {
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+ n = write(1, zeros, count < ARRAY_SIZE(zeros) ?
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+ count : ARRAY_SIZE(zeros));
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+
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+ if (n < 0)
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+ return -1;
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+
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+ count -= n;
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}
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return 0;