linux-kernel - Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected) [bug 12465]

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Message-ID: <20090222172758.GH6570@elte.hu>
Date:	Sun, 22 Feb 2009 18:27:58 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Kevin Shanahan <kmshanah@...b.org.au>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	bugme-daemon@...zilla.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected) [bug
	12465]


* Kevin Shanahan <kmshanah@...b.org.au> wrote:

> On Sun, 2009-02-15 at 11:04 +0100, Ingo Molnar wrote:
> > qemu-sy-4237 has been scheduled away, and the system appeared to have done
> > nothing in the meantime. That's not something that really looks like a
> > scheduler regression - there is nothing the scheduler can do if KVM
> > decides to block a task.
> > 
> > It would be nice to enhance this single-CPU trace some more - to more
> > surgically see what is going on. Firstly, absolute timestamps would be
> > nice:
> > 
> >   echo funcgraph-abstime  > trace_options
> >   echo funcgraph-proc     > trace_options
> > 
> > as it's a bit hard to see the global timescale of events.
> 
> I was going to try and grab the trace with absolute timestamps 
> tonight, but that option doesn't seem to be available in 
> Linus' current kernel.
> 
> flexo:/sys/kernel/debug/tracing# echo 0 > tracing_enabled
> flexo:/sys/kernel/debug/tracing# echo function_graph > current_tracer
> flexo:/sys/kernel/debug/tracing# echo funcgraph-proc > trace_options
> flexo:/sys/kernel/debug/tracing# echo funcgraph-abstime  > trace_options
> -su: echo: write error: Invalid argument
> flexo:/sys/kernel/debug/tracing# cat trace_options 
> print-parent nosym-offset nosym-addr noverbose noraw nohex nobin noblock
> nostacktrace nosched-tree ftrace_printk noftrace_preempt nobranch
> annotate nouserstacktrace nosym-userobj noprintk-msg-only
> nofuncgraph-overrun funcgraph-cpu funcgraph-overhead funcgraph-proc 
> flexo:/sys/kernel/debug/tracing# uname -a
> Linux flexo 2.6.29-rc5-00299-gadfafef #6 SMP Sun Feb 22 20:09:37 CST
> 2009 x86_64 GNU/Linux
> 
> What am I missing?

(replying here too - replied in the bugzilla already)

that's a feature of the latest tracing tree, so if you try -tip 
you'll have it.

	Ingo
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