linux-kernel - Re: 2.6.23-rt4 (was 2.6.23-rt1 trouble)

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Date:	Sat, 27 Oct 2007 15:43:45 +0100
From:	Rui Nuno Capela <rncbc@...bc.org>
To:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: 2.6.23-rt4 (was 2.6.23-rt1 trouble)

> On Mon, October 15, 2007 11:49, Rui Nuno Capela wrote:
>>
>> I am experiencing some highly annoying but intermitent freezing on a
>> pentium4 2.80G HT/SMT box, when doing normal desktop work with 2.6.23-rt1.
>>
>>
>> The same crippling behavior does not occur on a Core 2 Due T7200 2.0G
>> SMP, so I suspect it's something due specific to the SMT scheduling
>> support (Hyper-Threading). But can't tell for sure, obviously :)
>>
> 
> I was wrong. After several trials the same behavior also occurs on the
> Core2 Duo T7200. It just took longer to show its nasty.
> 
> 
>> The symptoms are noticeable primarily as some X/GUI intermitent freezing,
>> sometimes only one application, then several and ultimately the whole X 
>> desktop becomes completely unresponsive. It looks like scheduling 
>> problems. There is this hint that switching to a spare console terminal 
>> (via Ctrl+Alt+Fn) might cause later recovery. But its just a question of
>> some more time for it just happens again and again, one after another, 
>> several applications becoming temporarily frozen and just by luck the 
>> system gets back to normal, probably due to some incidental shake-up :) 
>> but there are other times that nothing seems to help with no alternative 
>> to the power-reset switch.
>>
>> I could not find any evidence on dmesg or in the system logs, of any
>> apparent trouble. No BUGs, no oops, no panics, no nothing. It just
>> freezes, this and that, now and then. It just makes it all unworkable
>> and obviously subject to ditching.
>>
>> Again, this only happens on this P4/HT box. On a Core2 Duo laptop, with
>> same 2.6.23-rt1 with the very same kernel configuration, it does not show 
>> any illness and is running quite fine.
>>
> 
> False. It used to run fine, until the creeps happen first time :(
> 
> 
>> Remember one report I had about a similar freezing behavior? Now it's
>> happening the other way around: the core2 is OK, the pentium4 is KO.
>>
> 
> Now it applies to all 2.6.23-rt1 images I could test upon.
> 
> 
>> One naive suspicion goes like the new rcu-preempt code is to blame, since
>> I don't remember having this or any other trouble with 2.6.23-rc8-rt1.
>>
> 
> Not be sure anymore, but this seems to be still a valid assumption.
> 

just to let you know that still the same trouble persists with 2.6.23.1-rt4

.config can be found here:
   http://www.rncbc.org/datahub/config-2.6.23.1-rt4.0


cheers.
-- 
rncbc aka Rui Nuno Capela
rncbc@...bc.org
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