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Improve precision of clock() function on Linux 

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
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6
ChangeLog
View File

@ -1,3 +1,9 @@
2013-06-13 Siddhesh Poyarekar <siddhesh@redhat.com>
[BZ #12515]
* sysdeps/unix/sysv/linux/clock.c (clock): Use result from
CLOCK_PROCESS_CPUTIME_ID clock instead of __times.
2013-06-11 Adhemerval Zanella <azanella@linux.vnet.ibm.com>
[BZ #15605]

22
NEWS
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@ -10,16 +10,16 @@ Version 2.18
* The following bugs are resolved with this release:
2546, 2560, 5159, 6809, 10060, 10062, 10357, 10686, 11120, 11561, 12387,
12723, 13550, 13889, 13951, 13988, 14142, 14176, 14200, 14256, 14280,
14293, 14317, 14327, 14478, 14496, 14582, 14686, 14812, 14888, 14894,
14908, 14920, 14952, 14964, 14981, 14982, 14985, 14991, 14994, 14996,
15000, 15003, 15006, 15007, 15014, 15020, 15023, 15036, 15054, 15055,
15062, 15078, 15084, 15085, 15086, 15100, 15160, 15214, 15221, 15232,
15234, 15283, 15285, 15287, 15304, 15305, 15307, 15309, 15327, 15330,
15335, 15336, 15337, 15339, 15342, 15346, 15359, 15361, 15366, 15380,
15381, 15394, 15395, 15405, 15406, 15409, 15416, 15418, 15419, 15423,
15424, 15426, 15429, 15441, 15442, 15448, 15465, 15480, 15485, 15488,
15490, 15493, 15497, 15506, 15529, 15536, 15553, 15577, 15583.
12515, 12723, 13550, 13889, 13951, 13988, 14142, 14176, 14200, 14256,
14280, 14293, 14317, 14327, 14478, 14496, 14582, 14686, 14812, 14888,
14894, 14908, 14920, 14952, 14964, 14981, 14982, 14985, 14991, 14994,
14996, 15000, 15003, 15006, 15007, 15014, 15020, 15023, 15036, 15054,
15055, 15062, 15078, 15084, 15085, 15086, 15100, 15160, 15214, 15221,
15232, 15234, 15283, 15285, 15287, 15304, 15305, 15307, 15309, 15327,
15330, 15335, 15336, 15337, 15339, 15342, 15346, 15359, 15361, 15366,
15380, 15381, 15394, 15395, 15405, 15406, 15409, 15416, 15418, 15419,
15423, 15424, 15426, 15429, 15441, 15442, 15448, 15465, 15480, 15485,
15488, 15490, 15493, 15497, 15506, 15529, 15536, 15553, 15577, 15583.
* CVE-2013-0242 Buffer overrun in regexp matcher has been fixed (Bugzilla
#15078).
@ -41,6 +41,8 @@ Version 2.18
* New <math.h> macro named issignaling to check for a signaling NaN (sNaN).
It is based on draft TS 18661 and currently enabled as a GNU extension.
* Improved precision of the clock() function on Linux.
Version 2.17

32
sysdeps/unix/sysv/linux/clock.c
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@ -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));
}