Date: Wed, 06 Sep 2000 12:25:53 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Josef Karthauser <joe@pavilion.net> Cc: current@FreeBSD.ORG, hackers@FreeBSD.ORG Subject: Re: looking for "microuptime went backwards" victims... Message-ID: <64554.968235953@critter> In-Reply-To: Your message of "Wed, 06 Sep 2000 11:17:13 BST." <20000906111713.E1081@pavilion.net>
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Uhm, that is from the sound driver, not from the timecounter...
Poul-Henning
In message <20000906111713.E1081@pavilion.net>, Josef Karthauser writes:
>I got this last night running 'mtv' on a system with heavy disk I/O.
>The errors were:
>
>Sep 5 23:12:14 genius /kernel: pcm0: hwptr went backwards 8208 -> 8192
>Sep 5 23:12:47 genius /kernel: pcm0: hwptr went backwards 8420 -> 8192
>Sep 5 23:12:57 genius /kernel: pcm0: hwptr went backwards 8212 -> 8192
>Sep 5 23:13:04 genius /kernel: pcm0: hwptr went backwards 8196 -> 8192
>Sep 5 23:13:21 genius /kernel: pcm0: hwptr went backwards 8208 -> 8192
>
>etc.
>
>Joe
>
>FreeBSD genius.systems.pavilion.net 5.0-CURRENT FreeBSD 5.0-CURRENT #11: Tue Sep 5 12:45:45 BST 2000 joe@genius.systems.pavilion.net:/usr/obj/usr/src/sys/GENIUS i386
>
>On Mon, Sep 04, 2000 at 06:41:14PM +0200, Poul-Henning Kamp wrote:
>>
>> I'm looking for the remaining victims of the dreaded "microuptime
>> went backwards" message.
>>
>> If you can reliably reproduce the problem, please contact me, so
>> we can arrange for some very detailed tracing to try to find out
>> what exactly is going on. I have not been able to trigger the
>> problem in my lab in a long time.
>>
>> If you see the message only occationally, please try the attached
>> patch and let me know if this changes the picture. The patch is
>> not meant as a fix, but it might reduce the impact of this condition
>> considerably when it happens. Basically by reducing the width of
>> the timecounter the magnitude of the hit we take if the timecounter
>> goes backwards is reduced from about an hour to approx 110msec.
>>
>> Reducing the width to less than 17 bits starts to run the risk of
>> ambiguity due to clock rollover.
>>
>> This patch may not be safe with PCAUDIO.
>>
>> Poul-Henning
>>
>> Index: clock.c
>> ===================================================================
>> RCS file: /home/ncvs/src/sys/i386/isa/clock.c,v
>> retrieving revision 1.155
>> diff -u -r1.155 clock.c
>> --- clock.c 2000/07/30 21:05:22 1.155
>> +++ clock.c 2000/09/04 16:34:16
>> @@ -194,7 +194,7 @@
>> static struct timecounter i8254_timecounter = {
>> i8254_get_timecount, /* get_timecount */
>> 0, /* no poll_pps */
>> - ~0u, /* counter_mask */
>> + 0x1ffff, /* counter_mask */
>> 0, /* frequency */
>> "i8254" /* name */
>> };
>>
>> --
>> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
>> phk@FreeBSD.ORG | TCP/IP since RFC 956
>> FreeBSD coreteam member | BSD since 4.3-tahoe
>> Never attribute to malice what can adequately be explained by incompetence.
>>
>>
>> To Unsubscribe: send mail to majordomo@FreeBSD.org
>> with "unsubscribe freebsd-hackers" in the body of the message
>
>--
>Josef Karthauser FreeBSD: How many times have you booted today?
>Technical Manager Viagra for your server (http://www.uk.freebsd.org)
>Pavilion Internet plc. [joe@pavilion.net, joe@uk.freebsd.org, joe@tao.org.uk]
>
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD coreteam member | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
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