linux-kernel - Re: recomended way to check longest period that interupts are disabled ?

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Date:	Thu, 26 Apr 2007 11:53:57 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Mike Mattie <codermattie@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: recomended way to check longest period that interupts are
	disabled ?

On Thu, 2007-04-26 at 02:13 -0700, Mike Mattie wrote:
> Hello,
> 
> I am still struggling to track down problems with audio playback. I get intermittent:
> 
> Apr 26 02:01:40 reforged [13230.947879] cannot submit sync urb (err = -45)
> 
> I have tackled the scheduler issues to where I really don't think the
> driver is being starved at all. I am running audacious like so:
> 
> schedtool -R -p 50 -n 1 -e audacious
> 
> At this point the strongest correlation I can get is that starting
> programs seems to trigger the stutter. I have suspected IO for
> some time.
> 
> My system image , / & /usr are on a libata (VIA PATA) driver.
> I have disabled the write-cache , but I also have noatime set
> on mount, for /usr
> 
> My big suspicion is that one of my drivers, likely IO is
> disabling interrupts for too long.
> 
> I have looked but not found a tool for measuring the longest
> period interrupts are disabled and pointing the finger at
> the culprit, could anyone on this list recommend tools that
> might help me pinpoint what is going on ?
> 
> I would also be delighted for any sort of recommended latency
> testing tools.
> 
> pin-pointing this is going to be a "learning experience" but
> every time I think I am about to have a bonding moment with 
> the kernel audio skips; I am highly motivated.

The -rt kernel contains a full latency tracer.

http://people.redhat.com/mingo/realtime-preempt/

Some hardware just isn't up to the job though...

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