From: Nick Craig-Wood <nick@memset.com>
To: Nix <nix@esperi.org.uk>
Cc: Jeff Dike <jdike@addtoit.com>,
user-mode-linux-devel@lists.sourceforge.net
Subject: Re: [uml-devel] uml-patch-2.4.26-2
Date: Fri, 30 Jul 2004 15:46:06 +0100 [thread overview]
Message-ID: <20040730144606.GA27236@memset.com> (raw)
In-Reply-To: <878yd1itow.fsf@amaterasu.srvr.nix>
On Fri, Jul 30, 2004 at 01:08:15PM +0100, Nix wrote:
> On Fri, 30 Jul 2004, Nick Craig-Wood said:
> > I'm having trouble getting this to run stably. On a Fedora core 2
> > image it locks up with 100% CPU after about 12 hours
> > normally.
>
> I think this is caused the patch to use gettimeofday(), which breaks if
> time ever moves backwards. Lots of other things break if time moves
> backwards, too, but most don't care if it moves backwards by only a
> second or so. UML does care.
>
> To work around it, avoid moving time backwards (ntpd and ntpdate both
> have switches to avoid this and always use adjtimex() instead.)
Yes you are right - Thanks! The time of the crash lined up exactly
with the time being reset on the host. I've changed it to use
adjtimex which should work around the problem.
However I view the above to be a bug in UML - it shouldn't lock up.
Its entitled to miss events etc though. gettimeofday(2) isn't
guaranteed to be monotonic, but unfortunately there isn't a monotonic
timer (like jiffies) that escapes to user space AFAIK.
( We've got a laptop in the office who's time jumps backwards (just by
a few ms) quite regularly due to buggy BIOS and speedstep. This
causes a few problems (notably with sawfish)... I even sent a patch
to fix this to LKML but it was deemed that the BIOS should be fixed
instead of the kernel )
--
Nick Craig-Wood Tel: 0800 195 4968 Net: nick@memset.com
Memset Ltd Web: http://www.memset.com
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next prev parent reply other threads:[~2004-07-30 14:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-07-16 20:19 [uml-devel] uml-patch-2.4.26-2 Jeff Dike
2004-07-30 7:48 ` Nick Craig-Wood
2004-07-30 12:08 ` Nix
2004-07-30 14:46 ` Nick Craig-Wood [this message]
2004-07-30 17:02 ` Adam Heath
2004-07-30 18:49 ` Jeff Dike
2004-07-30 19:14 ` Adam Heath
2004-07-30 17:36 ` Jeff Dike
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