linux-kernel - Re: NMI watchdog triggering during load

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Message-ID: <54F9C155.3050309@oracle.com>
Date:	Fri, 06 Mar 2015 08:01:41 -0700
From:	David Ahern <david.ahern@...cle.com>
To:	Mike Galbraith <efault@....de>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: NMI watchdog triggering during load_balance

On 3/5/15 9:52 PM, Mike Galbraith wrote:
>> CPU970 attaching sched-domain:
>>    domain 0: span 968-975 level SIBLING
>>     groups: 8 single CPU groups
>>     domain 1: span 968-975 level MC
>>      groups: 1 group with 8 cpus
>>      domain 2: span 768-1023 level CPU
>>       groups: 4 groups with 256 cpus per group
>
> Wow, that topology is horrid.  I'm not surprised that your box is
> writhing in agony.  Can you twiddle that?
>

twiddle that how?

The system has 4 physical cpus (sockets). Each cpu has 32 cores with 8 
threads per core and each cpu has 4 memory controllers.

If I disable SCHED_MC and CGROUPS_SCHED (group scheduling) there is a 
noticeable improvement -- watchdog does not trigger and I do not get the 
rq locks held for 2-3 seconds. But there is still fairly high cpu usage 
for an idle system. Perhaps I should leave SCHED_MC on and disable 
SCHED_SMT; I'll try that today.

Thanks,
David
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