linux-kernel - Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc

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Message-ID: <487091AE.8060702@grandegger.com>
Date:	Sun, 06 Jul 2008 11:34:38 +0200
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Luotao Fu <l.fu@...gutronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU issue?

Steven Rostedt wrote:
> On Wed, 2 Jul 2008, Wolfgang Grandegger wrote:
> 
>> Steven Rostedt wrote:
>>> On Tue, 1 Jul 2008, Wolfgang Grandegger wrote:
>>>> I continue this thread because it's still not understood why enabling
>>>> CONFIG_RCU_TRACE is necessary to get reasonable latencies on the
>>>> MPC5200. It might also explain, why I get much worse latencies with
>>>> 2.6.25.8-rt7.
>>> Have you tried turning on ftrace?
>> Hm, is it available for PowerPC? I have not found yet how to enable it.
> 
> Hmm, should be. But I need to test it on my PPC box first before I can
> tell you for sure. If you don't see a way to enable it, perhaps I haven't
> updated the config options for PPC yet.

I added HAVE_FTRACE and HAVE_DYNAMIC_FTRACE to "config PPC" but more 
seems to be missing, e.g. arch/powerpc/kernel/ftrace.c. Nevertheless, 
how would I trigger high latency events with ftrace. I there a 
description somewhere?

Wolfgang.

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