Date: Sun, 28 Jun 1998 13:40:51 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: John Hay <jhay@mikom.csir.co.za> Cc: freebsd-smp@FreeBSD.ORG Subject: Re: time problem? Message-ID: <2720.899034051@critter.freebsd.dk> In-Reply-To: Your message of "Sat, 28 Jun 1998 12:42:31 %2B0200." <199806281042.MAA04522@zibbi.mikom.csir.co.za>
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>I have found that my dual P5 100MHz machine will gain +- 0.85 seconds
>every now and again. [...]
>so it looks like it has something
>to do with the SMP code. It also does not seem to have anything to do
>with how busy the machine is, it has happened on a totally idle machine
>and also during a make world.
>
>Anybody have any ideas how I can look for this? I don't understand all
>the low level time stuff yet (especially the SMP side of it), but if
>given a little direction I'm willing to try a few things.
It is really very simple, and there is nothing SMP specific about the
code.
.85 seconds sounds suspiciosly like 2^20 cycles at 1193182 Hz.
Unfortunately that doesn't really make any kind of sense to me...
How do you detect this jump ? what is the exact sequnce of events ?
The only possibly weak spot I know is this test in i386/isa/clock.c,
you can try out this patch, but I doubt it will fix it.
Index: clock.c
===================================================================
RCS file: /home/ncvs/src/sys/i386/isa/clock.c,v
retrieving revision 1.124
diff -u -r1.124 clock.c
--- clock.c 1998/06/09 13:10:46 1.124
+++ clock.c 1998/06/28 11:39:03
@@ -1148,7 +1148,7 @@
high = inb(TIMER_CNTR0);
count = hardclock_max_count - ((high << 8) | low);
- if (count < i8254_lastcount) {
+ if (count <= i8254_lastcount) {
i8254_ticked = 1;
i8254_offset += hardclock_max_count;
}
--
Poul-Henning Kamp FreeBSD coreteam member
phk@FreeBSD.ORG "Real hackers run -current on their laptop."
"ttyv0" -- What UNIX calls a $20K state-of-the-art, 3D, hi-res color terminal
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