Subject: Re: [patch] Real-Time Preemption, -RT-2.6.11-rc3-V0.7.38-01
From: Lee Revell <rlrevell@joe-job.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>
In-Reply-To: <1108845942.10705.27.camel@krustophenia.net>
References: <20050204100347.GA13186@elte.hu>
	 <1108789704.8411.9.camel@krustophenia.net> <20050219090036.GA30456@elte.hu>
	 <20050219090312.GA30513@elte.hu>
	 <1108845942.10705.27.camel@krustophenia.net>
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Date: Thu, 17 Mar 2005 11:33:22 -0500
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On Sat, 2005-02-19 at 15:45 -0500, Lee Revell wrote:
> On Sat, 2005-02-19 at 10:03 +0100, Ingo Molnar wrote:
> > * Ingo Molnar <mingo@elte.hu> wrote:
> > 
> > > > Testing on an all SCSI 1.3Ghz Athlon XP system, I am seeing very long
> > > > latencies in the journalling code with 2.6.11-rc4-RT-V0.7.39-02.
> > > 
> > > could you send me the full trace?
> > 
> > just in case the system in question is still running - could you also do 
> > a 'verbose' trace via:
> > 
> > 	echo 1 > /proc/sys/kernel/trace_verbose
> 
> OK, here is a 2912us verbose latency trace with "data=ordered", gzipped.
> dbench 32 or 64 is the easiest way to trigger these.
> 
> I have not tried "data=journal".  As previously stated "data=writeback"
> works perfectly - I ran JACK overnight while stressing the fs and did
> not get one xrun.

Any update on this?  The problem is still apparent in 2.6.11.  It seems
to be a regression from 2.6.10.  And now I've heard 2.6.12-rc1 mentioned
with no motion on this.

Here's the trace again in case you missed it:

http://www.alsa-project.org/~rlrevell/2912us

The "latency regressions" thread was all sub-millisecond stuff which can
be ignored IMHO.  Still interesting because they are regressions after
all, but not a real world problem.

However this one can be several milliseconds.  It's a real problem.

I'd hate to have to ship 2.6.12 with a disclaimer that ext3 with
"data=ordered" is not suitable for the desktop (as it clearly violates
the stated desktop responsiveness goal of 1ms).

Lee

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