Date: Wed, 15 Jun 2011 20:09:54 -0400 From: Jung-uk Kim <jkim@FreeBSD.org> To: freebsd-current@FreeBSD.org Cc: Ian FREISLICH <ianf@clue.co.za> Subject: Re: Time keeping Issues with the low-resolution TSC timecounter Message-ID: <201106152009.56163.jkim@FreeBSD.org> In-Reply-To: <201106151819.32495.jkim@FreeBSD.org> References: <E1QWvkC-0001QH-Cj@clue.co.za> <201106151639.30308.jkim@FreeBSD.org> <201106151819.32495.jkim@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
--Boundary-00=_UnU+NA6KT35yX0f
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
On Wednesday 15 June 2011 06:19 pm, Jung-uk Kim wrote:
> On Wednesday 15 June 2011 04:39 pm, Jung-uk Kim wrote:
> > On Wednesday 15 June 2011 03:27 pm, Ian FREISLICH wrote:
> > > > > The problem I noticed first is that it takes unusually long
> > > > > until a key press is repeated. With the default eventtimer
> > > > > (HPET) it seems to take about 4s, which can be slightly
> > > > > improved by switching to i8254.
> > > > >
> > > > > The "error beep" seems to take longer than usual, too,
> > > > > and the system "feels sluggish" in general.
> > > > >
> > > > > An effect that is easier to measure is that the system is
> > > > > unable to properly keep the time. Again the problem is less
> > > > > severe when using i8254 instead of HPET:
> > > >
> > > > [SNIP]
> > > >
> > > > First of all, please do not mix timecounter issues with
> > > > eventtimer. They are not directly related.
> > > >
> > > > Can you please show me verbose boot messages *without* your
> > > > patch? Does "sysctl kern.timecounter.hardware=HPET" help
> > > > *without* touching eventtimers?
> > >
> > > I have the same issue with my system (Atom N270). The effect
> > > that I see is about 29 wall clock seconds are recorded as 1
> > > system second.
> >
> > Can please you send me output from the following?
> >
> > sh -c 'count=10; while [ $count -gt 0 ]; do count=$((count -
> > 1));\ sysctl kern.timecounter; sleep 1; done'
>
> The OP sent me some data. The following is cooked data from what I
> got:
>
> TSC Delta Elapsed Time
> ---------------+---------------+------------
> 2245026970
> 2249708604 4681634 0.3003693189
> 2255874998 6166394 0.3956301509
> 2260656402 4781404 0.3067704701
> 2261993048 1336646 0.0857579744
> 2264175164 2182116 0.1400025497
> 2266445706 2270542 0.1456758803
> 2266987003 541297 0.0347291162
> 2267645095 658092 0.0422225757
> 2268274965 629870 0.0404118782
> 2268979787 704822 0.0452207294
> 2270482069 1502282 0.0963850274
> 2271140877 658808 0.0422685136
>
> HPET Delta Elapsed Time
> ---------------+---------------+------------
> 1322734365
> 1337156221 14421856 1.0072408644
> 1351548130 14391909 1.0051493276
> 1365949265 14401135 1.0057936833
> 1380376349 14427084 1.0076059946
> 1394823985 14447636 1.0090413726
> 1409273964 14449979 1.0092050107
> 1423719753 14445789 1.0089123757
> 1438167064 14447311 1.0090186742
> 1452613630 14446566 1.0089666424
> 1467062977 14449347 1.0091608710
> 1481522037 14459060 1.0098392393
> 1495969404 14447367 1.0090225853
>
> As you can see, HPET increases normally (within errors from
> sleep(3) accuracy, syscall overhead, etc.) but TSC-low is totally
> erratic (and too low). I don't know how this can happen, though.
> :-(
>
> I need some time to figure it out.
Can you please test the attached patch? Theoretically, it should not
make a difference but I'd like to see if it does, just in case.
Thanks,
Jung-uk Kim
--Boundary-00=_UnU+NA6KT35yX0f
Content-Type: text/plain;
charset="iso-8859-1";
name="tsc.diff"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
filename="tsc.diff"
Index: sys/x86/x86/tsc.c
===================================================================
--- sys/x86/x86/tsc.c (revision 223102)
+++ sys/x86/x86/tsc.c (working copy)
@@ -579,6 +579,9 @@ tsc_get_timecount(struct timecounter *tc __unused)
static u_int
tsc_get_timecount_low(struct timecounter *tc)
{
+ uint32_t low, high;
- return (rdtsc() >> (int)(intptr_t)tc->tc_priv);
+ __asm __volatile("rdtsc; shrd %2,%1,%0"
+ : "=a" (low), "=d" (high) : "Ic" ((uint8_t)(intptr_t)tc->tc_priv));
+ return (low);
}
--Boundary-00=_UnU+NA6KT35yX0f--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201106152009.56163.jkim>