Date: Wed, 6 Sep 2000 11:17:13 +0100 From: Josef Karthauser <joe@pavilion.net> To: Poul-Henning Kamp <phk@FreeBSD.ORG> Cc: current@FreeBSD.ORG, hackers@FreeBSD.ORG Subject: Re: looking for "microuptime went backwards" victims... Message-ID: <20000906111713.E1081@pavilion.net> In-Reply-To: <53059.968085674@critter>; from phk@FreeBSD.ORG on Mon, Sep 04, 2000 at 06:41:14PM %2B0200 References: <53059.968085674@critter>
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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
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--
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]
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