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Significantly reduce the non-monotonicity of this function. 

The way time is apportioned to interrupt/system/user makes it impossible
to guarantee monotonicity except by saving the previous value!
This commit is contained in:
dsl 2003-08-19 08:31:18 +00:00
parent b83dd2f98b
commit 79b2073eea
1 changed files with 13 additions and 7 deletions
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20
lib/libc/gen/clock.c
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@ -1,4 +1,4 @@
/* $NetBSD: clock.c,v 1.8 2003/08/07 16:42:46 agc Exp $ */
/* $NetBSD: clock.c,v 1.9 2003/08/19 08:31:18 dsl Exp $ */
/*
* Copyright (c) 1989, 1993
@ -34,7 +34,7 @@
#if 0
static char sccsid[] = "@(#)clock.c 8.1 (Berkeley) 6/4/93";
#else
__RCSID("$NetBSD: clock.c,v 1.8 2003/08/07 16:42:46 agc Exp $");
__RCSID("$NetBSD: clock.c,v 1.9 2003/08/19 08:31:18 dsl Exp $");
#endif
#endif /* LIBC_SCCS and not lint */
@ -45,18 +45,24 @@ __RCSID("$NetBSD: clock.c,v 1.8 2003/08/07 16:42:46 agc Exp $");
#include <time.h>
/*
* Convert usec to clock ticks; could do (usec * CLOCKS_PER_SEC) / 1000000,
* but this would overflow if we switch to nanosec.
* This code is all rather silly because the kernel counts actual
* execution time (to usec accuracy) then splits it into user, system and
* interrupt based on when clock ticks happen. getrusage apportions the
* time based on the number of ticks, and here we are trying to generate
* a number which was, traditionally, the number of ticks!
*
* Due to the way the time is apportioned, this code (and indeed getrusage
* itself) are not guaranteed monotonic.
*/
#define CONVTCK(r) (r.tv_sec * CLOCKS_PER_SEC + \
r.tv_usec / (1000000 / CLOCKS_PER_SEC))
clock_t
clock()
{
struct rusage ru;
clock_t hz = CLOCKS_PER_SEC;
if (getrusage(RUSAGE_SELF, &ru))
return ((clock_t) -1);
return((clock_t)((CONVTCK(ru.ru_utime) + CONVTCK(ru.ru_stime))));
return (ru.ru_utime.tv_sec + ru.ru_stime.tv_sec) * hz +
(ru.ru_utime.tv_usec + ru.ru_stime.tv_usec + 50) / 100 * hz / 10000;
}