Date: Tue, 25 Jan 2000 08:58:36 +1100 From: Peter Jeremy <peter.jeremy@alcatel.com.au> To: stable@FreeBSD.org, FreeBSD-gnats-submit@FreeBSD.org Subject: Re: kern/13644 Message-ID: <00Jan25.085841est.115243@border.alcanet.com.au> In-Reply-To: <200001241659.LAA34219@misha.cisco.com>; from mi@aldan.algebra.com on Tue, Jan 25, 2000 at 04:02:28AM %2B1100 References: <14476.31150.689748.108097@onceler.kcilink.com> <200001241659.LAA34219@misha.cisco.com>
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On 2000-Jan-25 04:02:28 +1100, Mikhail Teterin <mi@aldan.algebra.com> wrote:
> It does not explain the consistent 9-10 msecs excess.
_That_ might be a bug. The select(2) delay is converted from a struct
timeval into ticks by tvtohz(). This routine rounds up to the next
tick and then adds 1 to the result (in both -stable and -current).
The `+1' would seem to be incorrect - even if you want to allow for
the current tick, a more reasonable estimate would be 0.5, not 1.
Based on a quick check, both Solaris 2.5 and Digital Unix (aka Tru64)
4.0D don't include this one tick over-estimate.
I believe one (only) of the following two patches should be applied:
Index: kern_clock.c
===================================================================
RCS file: /home/CVSROOT/src/sys/kern/kern_clock.c,v
retrieving revision 1.104
diff -u -r1.104 kern_clock.c
--- kern_clock.c 1999/12/08 10:02:12 1.104
+++ kern_clock.c 2000/01/24 21:51:27
@@ -271,9 +271,8 @@
* If the number of usecs in the whole seconds part of the time
* difference fits in a long, then the total number of usecs will
* fit in an unsigned long. Compute the total and convert it to
- * ticks, rounding up and adding 1 to allow for the current tick
- * to expire. Rounding also depends on unsigned long arithmetic
- * to avoid overflow.
+ * ticks, rounding up. Rounding also depends on unsigned long
+ * arithmetic to avoid overflow.
*
* Otherwise, if the number of ticks in the whole seconds part of
* the time difference fits in a long, then convert the parts to
@@ -305,10 +304,10 @@
ticks = 1;
} else if (sec <= LONG_MAX / 1000000)
ticks = (sec * 1000000 + (unsigned long)usec + (tick - 1))
- / tick + 1;
+ / tick;
else if (sec <= LONG_MAX / hz)
ticks = sec * hz
- + ((unsigned long)usec + (tick - 1)) / tick + 1;
+ + ((unsigned long)usec + (tick - 1)) / tick;
else
ticks = LONG_MAX;
if (ticks > INT_MAX)
Index: sys_generic.c
===================================================================
RCS file: /home/CVSROOT/src/sys/kern/sys_generic.c,v
retrieving revision 1.54
diff -u -r1.54 sys_generic.c
--- sys_generic.c 2000/01/14 02:53:25 1.54
+++ sys_generic.c 2000/01/24 21:50:26
@@ -687,7 +687,10 @@
ttv = atv;
timevalsub(&ttv, &rtv);
timo = ttv.tv_sec > 24 * 60 * 60 ?
- 24 * 60 * 60 * hz : tvtohz(&ttv);
+ 24 * 60 * 60 * hz + 1 : tvtohz(&ttv);
+ /* compensate for over-estimate in tvtohz() */
+ if (timo > 1)
+ timo--
}
s = splhigh();
if ((p->p_flag & P_SELECT) == 0 || nselcoll != ncoll) {
@@ -818,7 +821,10 @@
ttv = atv;
timevalsub(&ttv, &rtv);
timo = ttv.tv_sec > 24 * 60 * 60 ?
- 24 * 60 * 60 * hz : tvtohz(&ttv);
+ 24 * 60 * 60 * hz + 1 : tvtohz(&ttv);
+ /* compensate for over-estimate in tvtohz() */
+ if (timo > 1)
+ timo--
}
s = splhigh();
if ((p->p_flag & P_SELECT) == 0 || nselcoll != ncoll) {
Peter
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