Date: Thu, 22 Jan 2004 14:37:04 -0500
From: timothy parkinson <t@timothyparkinson.com>
To: john stultz <johnstul@us.ibm.com>
Cc: hauan@cmu.edu, Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: 2.6.1 "clock preempt"?
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hi john,

i think this sounds like the same issue that i've been seeing with 2.5/2.6
kernels for a while now.  smp kernel on a dual PIII machine without preempt.

after running for a while the "losing ticks" shows up in dmesg, and the system
loses a lot of time.  load seems to make it worse, so that just might be the
trigger.

i'll try that one-liner as well when i get a chance - you said that if the
system still loses time, that narrows it down to hardware, yes?

thanks...

timothy


On Wed, Jan 21, 2004 at 10:19:26AM -0800, john stultz wrote:
> On Wed, 2004-01-21 at 07:06, Steinar Hauan wrote:
> > On Tue, 2004-01-20 at 16:26, john stultz wrote:
> > > How quickly do you see this message? Does it happen right at boot time,
> > > or during load?
> > 
> > boottime:
> >   Jan 19 08:59:24 localhost kernel: Linux version 2.6.1
> >                         (root@offa) (gcc version 3.3.2 20031218
> >                         (Red Hat Linux 3.3.2-5)) #2 
> >                         SMP Sat Jan 17 18:05:09 EST 2004
> > 
> >   (yes, i have SMP enabled even for a single cpu machine; the kernel
> >    will be run on a multitude of machines of which most are SMP)
> > 
> > log messages prior to time issues:
> > 
> > Jan 20 04:02:01 localhost anacron[6057]: Updated timestamp for 
> >                                              job `cron.daily' to
> > 2004-01-20
> > Jan 20 04:05:38 localhost kernel: hdb: dma_timer_expiry:
> >                                              dma status == 0x61
> > Jan 20 04:05:48 localhost kernel: hdb: DMA timeout error
> > Jan 20 04:05:48 localhost kernel: hdb: dma timeout error:
> >                                              status=0xd0 {Busy }
> > Jan 20 04:05:48 localhost kernel: hda: DMA disabled
> > Jan 20 04:05:48 localhost kernel: hdb: DMA disabled
> > Jan 20 04:05:48 localhost kernel: ide0: reset: success
> > 
> > (hda and hdb are on the same controller; the only active disk at
> >  this time should be hda ... hdb should be essentially idle
> >  except for cron.daily scripts running around then)
> > 
> > timing error starts here; interactive work
> > 
> > Jan 20 07:52:40 localhost kernel: Losing too many ticks!
> 
> Hmm. It might be that IDE PIO mode on your system blocks interrupts for
> too long.
> 
> > > You might want to try the attached patch to see if we're overreacting
> > [...]
> > > Also, do you see the problem when preempt is disabled 
> > 
> > testing overnight failed to reproduce the problem. note that the
> > original event only occurred after about 12 hrs of testing.
> 
> Sorry, that was vague. Did you fail to reproduce the problem using the
> patch or with preempt disabled?
> 
> > i'll install lm_sensors & smarttools and run cpuburn for a while
> > to ensure this is not related to any hardware issues.
> 
> I doubt its its a hardware fault issue, but more likely some driver not
> working properly with your hardware and blocking interrupts for too
> long. 
> 
> thanks
> -john
> 
> -
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