From owner-freebsd-hackers Wed Sep 6 3:17:23 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from genius.systems.pavilion.net (genius.systems.pavilion.net [212.74.1.100]) by hub.freebsd.org (Postfix) with ESMTP id 4BE4B37B423; Wed, 6 Sep 2000 03:17:14 -0700 (PDT) Received: by genius.systems.pavilion.net (Postfix, from userid 100) id 79EB09B40; Wed, 6 Sep 2000 11:17:13 +0100 (BST) Date: Wed, 6 Sep 2000 11:17:13 +0100 From: Josef Karthauser To: Poul-Henning Kamp Cc: current@FreeBSD.ORG, hackers@FreeBSD.ORG Subject: Re: looking for "microuptime went backwards" victims... Message-ID: <20000906111713.E1081@pavilion.net> Mail-Followup-To: Josef Karthauser , Poul-Henning Kamp , current@FreeBSD.ORG, hackers@FreeBSD.ORG References: <53059.968085674@critter> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <53059.968085674@critter>; from phk@FreeBSD.ORG on Mon, Sep 04, 2000 at 06:41:14PM +0200 X-NCC-RegID: uk.pavilion Organisation: Pavilion Internet plc, Lees House, 21-23 Dyke Road, Brighton, England Phone: +44-845-333-5000 Fax: +44-845-333-5001 Mobile: +44-403-596893 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG 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] To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message