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Provide high precision conversion from ns,us,ms -> sbintime in kevent

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In timer2sbintime(), calculate the second and fractional second portions of
the sbintime separately. When calculating the the fractional second portion,
use a 64bit multiply to prevent excess truncation. This avoids the ~7% error
in the original conversion for ns, and smaller errors of the same type for us
and ms.

PR: 198139
Reviewed by: jhb
MFC after: 1 week
Differential Revision:    https://reviews.freebsd.org/D5397
This commit is contained in:
Justin T. Gibbs 2016-03-12 23:02:53 +00:00
parent 823590d40e
commit 5405e7e2ee
1 changed files with 44 additions and 19 deletions
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63
sys/kern/kern_event.c
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@ -564,34 +564,59 @@ knote_fork(struct knlist *list, int pid)
#define NOTE_TIMER_PRECMASK (NOTE_SECONDS|NOTE_MSECONDS|NOTE_USECONDS| \
NOTE_NSECONDS)
static __inline sbintime_t
static sbintime_t
timer2sbintime(intptr_t data, int flags)
{
sbintime_t modifier;
/*
* Macros for converting to the fractional second portion of an
* sbintime_t using 64bit multiplication to improve precision.
*/
#define NS_TO_SBT(ns) (((ns) * (((uint64_t)1 << 63) / 500000000)) >> 32)
#define US_TO_SBT(us) (((us) * (((uint64_t)1 << 63) / 500000)) >> 32)
#define MS_TO_SBT(ms) (((ms) * (((uint64_t)1 << 63) / 500)) >> 32)
switch (flags & NOTE_TIMER_PRECMASK) {
case NOTE_SECONDS:
modifier = SBT_1S;
break;
#ifdef __LP64__
if (data > (SBT_MAX / SBT_1S))
return SBT_MAX;
#endif
return ((sbintime_t)data << 32);
case NOTE_MSECONDS: /* FALLTHROUGH */
case 0:
modifier = SBT_1MS;
break;
case NOTE_USECONDS:
modifier = SBT_1US;
break;
case NOTE_NSECONDS:
modifier = SBT_1NS;
break;
default:
return (-1);
}
if (data >= 1000) {
int64_t secs = data / 1000;
#ifdef __LP64__
if (data > SBT_MAX / modifier)
return (SBT_MAX);
if (secs > (SBT_MAX / SBT_1S))
return SBT_MAX;
#endif
return (modifier * data);
return (secs << 32 | MS_TO_SBT(data % 1000));
}
return MS_TO_SBT(data);
case NOTE_USECONDS:
if (data >= 1000000) {
int64_t secs = data / 1000000;
#ifdef __LP64__
if (secs > (SBT_MAX / SBT_1S))
return SBT_MAX;
#endif
return (secs << 32 | US_TO_SBT(data % 1000000));
}
return US_TO_SBT(data);
case NOTE_NSECONDS:
if (data >= 1000000000) {
int64_t secs = data / 1000000000;
#ifdef __LP64__
if (secs > (SBT_MAX / SBT_1S))
return SBT_MAX;
#endif
return (secs << 32 | US_TO_SBT(data % 1000000000));
}
return NS_TO_SBT(data);
default:
break;
}
return (-1);
}
static void