linux-kernel - Re: [Bug #12208] uml is very slow on 2.6.28 host

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Message-ID: <20081218143752.GB10548@elte.hu>
Date:	Thu, 18 Dec 2008 15:37:52 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>
Cc:	Miklos Szeredi <miklos@...redi.hu>, rjw@...k.pl,
	a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org
Subject: Re: [Bug #12208] uml is very slow on 2.6.28 host


* Mike Galbraith <efault@....de> wrote:

> On Tue, 2008-12-16 at 16:27 +0100, Miklos Szeredi wrote:
> 
> > Is there a way to trace what is happening in the scheduler?
> 
> Sure.  Ingo has a script for gathering info (attached), if you run it, 
> please gzip up the output and send me a copy offline to eyeball.
> 
> There's also ftrace, but I've not tried that yet, so can't offer any 
> advice, I use primitive but effective time_after() + printk() with klogd 
> wakeup disabled (deadlock).

btw., there's a recent commit:

  32a7600: printk: make printk more robust by not allowing recursion

since then printk shouldnt deadlock anymore, even if called from within 
the scheduler.

Btw., ftrace_printk() can be used similarly (and you can capture it 
nonstop via /debug/tracing/trace_pipe), and should not deadlock either.

	Ingo
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