Date: Sat, 20 Nov 2004 21:40:35 +0100
From: Florian Schmidt <mista.tapas@gmx.net>
To: Florian Schmidt <mista.tapas@gmx.net>
Cc: Lee Revell <rlrevell@joe-job.com>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Rui Nuno Capela <rncbc@rncbc.org>,
       Mark_H_Johnson@Raytheon.com, "K.R. Foley" <kr@cybsft.com>,
       Bill Huey <bhuey@lnxw.com>, Adam Heath <doogie@debian.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Michal Schmidt <xschmi00@stud.feec.vutbr.cz>,
       Fernando Pablo Lopez-Lezcano <nando@ccrma.Stanford.EDU>,
       Karsten Wiese <annabellesgarden@yahoo.de>,
       Gunther Persoons <gunther_persoons@spymac.com>, emann@mrv.com,
       Shane Shrybman <shrybman@aei.ca>, Amit Shah <amit.shah@codito.com>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.29-0
Message-ID: <20041120214035.2deceaeb@mango.fruits.de>
In-Reply-To: <20041120201155.6dc43c39@mango.fruits.de>
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	<20041117124234.GA25956@elte.hu>
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	<20041118164612.GA17040@elte.hu>
	<1100920963.1424.1.camel@krustophenia.net>
	<20041120125536.GC8091@elte.hu>
	<1100971141.6879.18.camel@krustophenia.net>
	<20041120191403.GA16262@elte.hu>
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On Sat, 20 Nov 2004 20:11:55 +0100
Florian Schmidt <mista.tapas@gmx.net> wrote:

> 29-4 with PREEMPT works very good (jackd at 64 frames: 0 xruns (running for
> 1h now), soundcard irq unthreaded). Opposed to 29-1 PREEMPT_REALTIME which
> showed some very weird jackd behaviour (xruns from 10usec to 50msec [!!!]).
> rtc_wakeup was showing no large jitter for that kernel though, nor did the
> different traces show anything that might have caused the jackd xruns. And
> yes, i configured the irq handlers sanely :)
> 
> Will build 29-4 PREEMPT_REALTIME now and see how this one behaves.

Pretty much as bad as 29-1. Sadly i have no idea on how to find out what is
causing jackd to act so weird under a PREEMPT_REALTIME kernel. It seems
there is some correlation to activity on X. Hiding and showing windows has a
certain chance of triggering a large xrun.

Hmm, the max jitter rtc_wakeup shows at 1024hz is around 150us. Which seems
a tiny bit large, too, as the rtc histogram shows a max wakeup latency of
16us..

It seems it's not the threaded irq handlers as jackd peformed quite well
under 29-4 PREEMPT with the soundcrd irq handler threaded and at high prio
(which i forgot to mention in my previous mail).

So i don't really know how to go about this. I suppose i just run PREEMPT
kernels instead of PREEMPT_REALTIME. Maybe it's the overhead which is
killing jackd performance with PREEMPT_REALTIME, but i don't believe so
(50ms? nah!).

flo

P.S.: There's so many variables in this PREEMPT/PREEMPT_REALTIME, handlers
threaded/unthreaded. IRQ handler thread priorities. It would probably be
cool if we could create some testing procedure which produces results which
are comparable. Ideally this procedure would be automated. Any takers?
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