linux-kernel - Re: Another preempt folding issue?

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Message-ID: <53062165.3040202@canonical.com>
Date:	Thu, 20 Feb 2014 16:38:13 +0100
From:	Stefan Bader <stefan.bader@...onical.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Borislav Petkov <bp@...en8.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>,
	MASAO TAKAHASHI <masao-takahashi@...no.co.jp>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: Another preempt folding issue?

On 14.02.2014 18:21, Peter Zijlstra wrote:
> On Fri, Feb 14, 2014 at 06:02:32PM +0100, Stefan Bader wrote:
>> One thing I likely should do is to reinstall the exact same laptop with 64bit
>> kernel and userspace... maybe only 64bit kernel first... and make sure on my
>> side that this does not show up on 64bit, too. I took the word of reporters for
>> that (and the impression that otherwise many more people would have complained).
> 
> Yeha, I'm going to try and install some 32bit userspace on a usb
> harddisk I've got and see if I can boot my Core2 laptop from that to try
> and reproduce.
> 
> But all that is probably going to be Monday :/
> 
*sigh* Already Thursday...

Peter, did you get to reproduce this locally? Unfortunately I had some
interruption and have not more Information than on last Friday (which is that
the same hw but 64bit kernel does not show it).

Meanwhile I wonder whether it would make sense to push the following (or more?)
to stable for 3.13.y:

1) 16824255394f55adf31b9a96a9965d8c15bdac4c
   x86, acpi, idle: Restructure the mwait idle routines
2) 7e98b71920464b8d15fa95c74366416cd3c88861
   x86, idle: Use static_cpu_has() for CLFLUSH workaround, add barriers
3) 8cb75e0c4ec9786b81439761eac1d18d4a931af3
   sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding
4) 215393bc1fab3d61a5a296838bdffce22f27ffda
   sched/preempt/x86: Fix voluntary preempt for x86

1+2 would be to avoid touching 3 too much and looked to be improvements on their
own. 3+4 would be cherry-picks if not for some fuzz 2.
I saw a few more things labelled preempt between 3.13 and current HEAD but am
not sure whether or which of those are strictly required. Namely some fixing to
preempt_enable_no_resched() mis-usage and maybe one fixing an issue of ftrace
locking up.

-Stefan
3


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