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

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Message-ID: <4874B9D5.1020309@grandegger.com>
Date:	Wed, 09 Jul 2008 15:15:01 +0200
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Luotao Fu <l.fu@...gutronix.de>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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?

Hi Fu (without n)

Luotao Fu wrote:
> Hi Wolfgang,
> 
> Wolfgang Grandegger wrote:
>> Hi Fun,
> 
> What's so funny? ;-)

Ah, oh, just a funny typo ;-).

> [...]
> 
>> But as Steven pointed out, the preempt_enable_noresched at that place
>>  might be illegal, anyway. In 2.6.25-rt, trace_mark() is no longer
>> used and I do not see an improvement with CONFIG_RCU_TRAC any more.
>> Latencies go up to 600us. I also tried with CONFIG_RCU_BOOST
>> disabled, but it did not improve the latencies. Actually, I still
>> measure significantly different latencies with 2.6.24.4-rt4,
>> 2.6.24.7-rt14 and 2.6.25.8-rt7, which is quite frustrating. As you
>> seem not be able to reproduce my high latencies, I wonder if there
>> are some toolchain or glibc related issues.
> 
> I took a quick look into the rcppreempt boost stuff in 2.6.24-rt and
> 2.6.25-rt. As you have mentioned, trace_mark is no more used in
> 2.6.24-rt. Instead of that flags are used to detect if the task is
> preempted. It might indeed probably be some toolchain issue.
> My powerpc toolchain I'm using here contains gcc 4.1.2 and glibc 2.5

OK, in the past you have been able to reproduce the high latencies with 
2.6.24-rt1 and CONFIG_RCU_TRACE disabled, IIRC. Did you use a different 
toolchain at that time?

Wolfgang.
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