linux-kernel - Re: smp_call_function

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Message-ID: <551C6A48.9060805@canonical.com>
Date:	Wed, 01 Apr 2015 16:59:36 -0500
From:	Chris J Arges <chris.j.arges@...onical.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Rafael David Tinoco <inaddy@...ntu.com>,
	Peter Anvin <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gema Gomez <gema.gomez-solano@...onical.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: smp_call_function_single lockups

On 04/01/2015 11:14 AM, Linus Torvalds wrote:
> On Wed, Apr 1, 2015 at 9:10 AM, Chris J Arges
> <chris.j.arges@...onical.com> wrote:
>>
>> Even with irqbalance removed from the L0/L1 machines the hang still occurs.
>>
>> This results in no 'apic: vector* or 'ack_APIC*' messages being displayed.
> 
> Ok. So the ack_APIC debug patch found *something*, but it seems to be
> unrelated to the hang.
> 
> Dang. Oh well.  Back to square one.
> 
>                            Linus
> 

With my L0 testing I've normally used a 3.13 series kernel since it
tends to reproduce the hang very quickly with the testcase. Note we have
reproduced an identical hang with newer kernels (3.19+patches) using the
openstack tempest on openstack reproducer, but the timing can vary
between hours and days.

Installing a v4.0-rc6+patch kernel on L0 makes the problem very slow to
reproduce, so I am running these tests now which may take day(s).

It is worthwhile to do a 'bisect' to see where on average it takes
longer to reproduce? Perhaps it will point to a relevant change, or it
may be completely useless.

--chris

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