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[PATCH][BZ #12515] Improve precision of clock function
- From: Siddhesh Poyarekar <siddhesh at redhat dot com>
- To: libc-alpha at sourceware dot org
- Date: Tue, 21 May 2013 20:26:11 +0530
- Subject: [PATCH][BZ #12515] Improve precision of clock function
Hi,
The current implementation of clock() uses times(), which only has
millisecond precision. Attached patch uses clock_gettime
(CLOCK_PROCESS_CPUTIME_ID) if it is available so as to improve the
precision to at least to the extent of CLOCKS_PER_SECOND, which comes
to about a microsecond. No regressions on x86_64. I'll add a note in
NEWS as well if this is acked. OK to commit?
Siddhesh
[BZ #12515]
* sysdeps/unix/sysv/linux/clock.c (clock): Use result from
CLOCK_PROCESS_CPUTIME_ID clock if available.
diff --git a/sysdeps/unix/sysv/linux/clock.c b/sysdeps/unix/sysv/linux/clock.c
index 5268d33..05a7c02 100644
--- a/sysdeps/unix/sysv/linux/clock.c
+++ b/sysdeps/unix/sysv/linux/clock.c
@@ -23,6 +23,14 @@
clock_t
clock (void)
{
+ struct timespec ts;
+
+ if (__clock_gettime (CLOCK_REALTIME, &ts) == 0)
+ return (clock_t) ((ts.tv_nsec * CLOCKS_PER_SEC) / 1000000000
+ + ts.tv_sec * CLOCKS_PER_SEC);
+
+ /* clock_gettime failed. This will only occur if CLOCK_PROCESS_CPUTIME_ID is
+ * not supported by the kernel. Fall back to __times. */
struct tms buf;
long clk_tck = __sysconf (_SC_CLK_TCK);