linux-kernel - Re: [ANNOUNCE] 3.14.3-rt5

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Message-ID: <20140513154002.GD15049@linutronix.de>
Date:	Tue, 13 May 2014 17:40:02 +0200
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: [ANNOUNCE] 3.14.3-rt5

* Mike Galbraith | 2014-05-10 06:15:03 [+0200]:

>On Fri, 2014-05-09 at 20:12 +0200, Sebastian Andrzej Siewior wrote:
>
>> Known issues:
>> 
>>       - bcache is disabled.
>> 
>>       - lazy preempt on x86_64 leads to a crash with some load.
>
>That is only with NO_HZ_FUL enabled here.  Box blows the stack during
>task exit, eyeballing hasn't spotted the why.

Even if I disable NO_HZ_FULL it explodes as soon as hackbench starts.

>> - CPU hotplug works in general. Steven's test script however
>>         deadlocks usually on the second invocation.
>
>My 64 core box runs for up to 14 hours, and never deadlocks.. it
>explodes in what looks like it should be an impossible manner instead.

It deadlocks here and I haven't figured the exact root cause. From what
it looks like is that the irq thread blocks on something during startup
(migrate_disable() or so). One of the blocked irq thrad is disk driver.
The userland tasks then block on ext4 in order to complete the requests.

I also noticed that the frequent cpu up/down fails at some point and my
kvm guest has just 7 out 8 CPUs. That one CPU remains dead and can't get
back online. Once that happens, the deadlock is comming in a few minutes
:)

>-Mike

Sebastian
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