linux-kernel - Re: [BUG] Strange 1-second pauses during Resume-from-RAM

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Message-ID: <20071202154746.GA27069@elte.hu>
Date:	Sun, 2 Dec 2007 16:47:46 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jörn Engel <joern@...fs.org>
Cc:	Mark Lord <lkml@....ca>, Pavel Machek <pavel@....cz>,
	Mark Lord <liml@....ca>, Thomas Gleixner <tglx@...utronix.de>,
	len.brown@...el.com, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	rjw@...k.pl
Subject: Re: [BUG] Strange 1-second pauses during Resume-from-RAM


* Jörn Engel <joern@...fs.org> wrote:

> I do.  Went through 10odd runs and annotated the function right below 
> mcount each time.  Seems to work now.
> 
> Trouble is that it doesn't solve my real problem at hand.  Something 
> is causing significant delays when writing to logfs.  Core logfs code 
> is not running, but may cause whatever other code is running and 
> burning up all the cpu time.  Wasting 100ms of "qemu-time" to write a 
> single page happens fairly frequently.
> 
> With the latency tracer the problem appears to have become worse.  Now 
> the loftlockup code triggers quite frequently.  Which makes a bit of 
> sense, as the problem is a busy CPU, rather than an idle one.

well what does the trace say, where do the delays come from? To get a 
quick overview you can make tracing lighter weight by doing:

 echo 0 > /proc/sys/kernel/mcount_enabled
 echo 1 > /proc/sys/kernel/trace_syscalls

(this turns the latency tracer into a "global strace" kind of tracer)

	Ingo
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