Message-ID: <422F07C2.7080900@cybsft.com>
Date: Wed, 09 Mar 2005 08:27:14 -0600
From: "K.R. Foley" <kr@cybsft.com>
Organization: Cybersoft Solutions, Inc.
User-Agent: Mozilla Thunderbird 1.0 (X11/20041206)
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To: Lee Revell <rlrevell@joe-job.com>
CC: linux-kernel <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       "Jack O'Quin" <joq@io.com>, Andrew Morton <akpm@osdl.org>
Subject: Re: 2.6.11 low latency audio test results
References: <1110324852.6510.11.camel@mindpipe>
In-Reply-To: <1110324852.6510.11.camel@mindpipe>
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Lee Revell wrote:
> OK, I have run some simple tests with JACK, Hydrogen, and 2.6.11.
> 
> 2.6.11 does not seem to be much of an improvement over 2.6.10.  It may
> in fact be slightly worse.  This was what I expected, as it appears that
> a number of latency fixes in the VM got preempted by the 4-level page
> tables merge.
> 
> At 32 frames (0.667 ms latency) I get an xrun about every 10-20 seconds,
> just running JACK and Hydrogen.
> 
> At 64 frames (1.33 ms latency) it's better, but I can easily cause
> massive xruns with "dbench 32".
> 
> At 128 frames (2.66 ms) it seems to work pretty well.
> 
> Overall, this puts us about even with Windows XP, and somewhat worse
> than Mac OS X.
> 
> Of course all of the above settings provide flawless xrun-free
> performance with 2.6.11-rc4 + PREEMPT_RT.
> 

The above mentioned patch will apply (and build and run) just fine to 
2.6.11 if you fix the EXTRAVERSION portion of the patch to not expect -rc4.

> Until Ingo releases the RT preempt patch for 2.6.11, I can't provide
> details, because the vanilla kernel lacks sufficient instrumentation.
> But the above results should help us move in the right direction.
> 
> Given the above results, and the performance of the RT patched kernel,
> I don't see why 2.6.12 should not be able to solidly outperform Windows
> and Mac in this area.
> 
> See the "Latency regressions" thread for some areas that might need
> attention.
> 
> Lee
> 
> 
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