linux-kernel - Re: [patch-3.18.7-rt1] sched/context-tracking: fix PREEMPT

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Date:	Mon, 09 Mar 2015 15:45:41 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
CC:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
	John Kacur <jkacur@...hat.com>
Subject: Re: [patch-3.18.7-rt1] sched/context-tracking: fix PREEMPT_LAZY explosions

On 03/09/2015 03:36 PM, Mike Galbraith wrote:
> On Mon, 2015-03-09 at 14:45 +0100, Sebastian Andrzej Siewior wrote:
>> * Mike Galbraith | 2015-02-18 12:21:54 [+0100]:
>>
>>> On Mon, 2015-02-16 at 12:18 +0100, Sebastian Andrzej Siewior wrote:
>>>
>>>> Known issues:
>>>>
>>>>       - lazy preempt on x86_64 leads to a crash with some load.
>>>
>>> The below still works for me.  (it doesn't make nohz_full actually work
>>> in rt, but at least folks who want to tinker with it can do so)
>> So your box still crashes without it?
>>
>> The thing is I tried to reproduce it and it does not occur anymore.
>> Neither in KVM nor on real HW.
> 
> Heh, well that's interesting, I just presumed it would still explode
> because you said it would.  I'll beat on it any let you know if I'm
> carrying a placebo patch or not :)

Hehe. By the time I did 3.18-rt1 I was surprised that the disable-
lazy-preempt-on-x8664 was still there because I assumed it has been
fixed in the v3.14 series. So I left it as-is (including the broken
message) and wanted to drop later an eye on it. And after you dropped a
few patches to fix it I assumed (even more) that it is still broken :)

> 
> 	-Mike
> 

Sebastian
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