lib/glibc
1
0
Fork 0
mirror of https://sourceware.org/git/glibc.git synced 2025-07-29 11:41:21 +03:00
Code Activity

Improve precision of clock() function on Linux

Browse Source 
Resolves #12515.

Use CLOCK_PROCESS_CPUTIME_ID instead of times to get better precision
in the value returned by clock.
This commit is contained in:
Siddhesh Poyarekar
2013-06-13 09:54:35 +05:30
parent 6a97b62a5b
commit 58206c6863
3 changed files with 32 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
sysdeps/unix/sysv/linux/clock.c
View File

@ -1,4 +1,5 @@
/* Copyright (C) 1991-2013 Free Software Foundation, Inc.
/* Return the time used by the program so far (user time + system time).
Copyright (C) 1991-2013 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@ -19,26 +20,21 @@
#include <time.h>
#include <unistd.h>
/* Return the time used by the program so far (user time + system time). */
#if CLOCKS_PER_SEC != 1000000l
# error "CLOCKS_PER_SEC should be 1000000"
#endif
clock_t
clock (void)
{
struct tms buf;
long clk_tck = __sysconf (_SC_CLK_TCK);
struct timespec ts;
/* We don't check for errors here. The only error the kernel
returns is EFAULT if the value cannot be written to the struct we
pass a pointer to. Otherwise the kernel returns an `unsigned
long' value which is the number of jiffies since system start.
But this number can be negative (when read as `long') when the
system is up for some time. Ignoring errors should therefore
have no negative impacts but solve the problem. */
__times (&buf);
/* clock_gettime shouldn't fail here since CLOCK_PROCESS_CPUTIME_ID is
supported since 2.6.12. Check the return value anyway in case the kernel
barfs on us for some reason. */
if (__glibc_unlikely (__clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &ts) != 0))
return (clock_t) -1;
return
(clk_tck <= CLOCKS_PER_SEC)
? ((unsigned long) buf.tms_utime + buf.tms_stime) * (CLOCKS_PER_SEC
/ clk_tck)
: ((unsigned long) buf.tms_utime + buf.tms_stime) / (clk_tck
/ CLOCKS_PER_SEC);
return (ts.tv_sec * CLOCKS_PER_SEC
+ ts.tv_nsec / (1000000000 / CLOCKS_PER_SEC));
}