linux-kernel - Re: Driver snd-hrtimer - causing system freeze with Rosegarden

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Date:	Thu, 10 Dec 2009 09:16:51 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	"wzabolot@...ktron.elka.pw.edu.pl" <W.Zabolotny@...a.pw.edu.pl>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Driver snd-hrtimer - causing system freeze with Rosegarden

At Wed, 09 Dec 2009 23:04:30 +0100,
wzabolot@...ktron.elka.pw.edu.pl wrote:
> 
> Dear Takashi,
> 
> I've sent the attached message to the LKML, but I think that it may be
> also reasonable to contact you - the author of the snd-hrtimer.
> I've tried to find reasons for instability of system running the
> sequencer using HR timer.
> My results are summarized in the attached bug report.
> Could you please check if calling of hrtimer_cancel from
> xnd_hrtimer_stop, which sometimes is called from the callback may cause
> the obderved instability?

hrtimer_cancel() is very simple and doesn't sleep (but spins).  So,
this shouldn't be the real issue.

> I have tested the problem on two SMP machines with diffrent kernels
> (2.6.30, 2.6.31.6, 2.6.32).
> The problem seems to be associated with the "snd-hrtimer" module.
> I've tried to run the application vie remote X session, while having the
> text console active.
> Before the machine froze, the following messages have been displayed in
> the console:
> 
> System 1 (Intel(R) Pentium(R) 4 CPU 2.80GHz HT)
> 
> hrtimer: interrupt too slow, forcing clock min delta to 3568 ns
> 
> System 2 (Intel(R) Core(TM)2 CPU         T5500  @ 1.66GHz)
> hrtimer: interrupt too slow, forcing clock min delta to 11103 ns
> CE: hpet increasing min_delta_ns to 15000 nsec
> CE: hpet increasing min_delta_ns to 22500 nsec
> CE: hpet increasing min_delta_ns to 33750 nsec

Hm, this sounds weird.
Does hrtimer work reliably on your machine?

> Analyzing the problem, I had an idea, that maybe the snd-hrtimer should
> be rewritten to call
> the callback via tasklet (I attach my patch only as an ilustration, my
> code doesn't work either),

Basically snd-hrtimer already uses tasklet (more exactly, snd-timer
handles callbacks in tasklet as default except for the objects with
SNDRV_TIMER_HW_TASKLET).  So your patch is wrapping over a wrap.


Takashi
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