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

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Date:	Sun, 2 Dec 2007 21:30:16 +0100
From:	Jörn Engel <joern@...fs.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jörn Engel <joern@...fs.org>,
	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

On Sun, 2 December 2007 21:07:22 +0100, Ingo Molnar wrote:
> * Jörn Engel <joern@...fs.org> wrote:
> 
> > Result looked like a livelock and finally convinced me to abandon the 
> > latency tracer.  Sorry, but it appears to be the right tool for the 
> > wrong job.
> 
> hm, we routinely use it in -rt to capture "what on earth is happening" 
> incidents. The snippet below is a random snipped from a trace that i've 
> just captured, with mcount enabled. It seems to work fine here, with and 
> without mcount. (pit clocksource is almost never used, that's why you 
> had those early problems.)
> 
> oprofile helps if you can reliably reproduce the slowdown in a loop or 
> for a long amount of time, with lots of CPU utilization - and then it's 
> also lower overhead. The tracer can be used to capture rare or complex 
> events, and gives the full flow control and what is happening within the 
> kernel.

Such a trace would be useful indeed.  But so far the patch has only
given me grief and nothing remotely like useful output.  Maybe I should
simply use the complete -rt patch instead of debugging the broken-out
latency-tracer patch.

Jörn

-- 
Mundie uses a textbook tactic of manipulation: start with some
reasonable talk, and lead the audience to an unreasonable conclusion.
-- Bruce Perens
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