linux-kernel - Re: False-positive RCU stall warnings on large systems...

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Message-ID: <20130219181624.GG3093@linux.vnet.ibm.com>
Date:	Tue, 19 Feb 2013 10:16:24 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Daniel J Blueman <daniel@...ascale-asia.com>
Cc:	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	Steffen Persvold <sp@...ascale.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: False-positive RCU stall warnings on large systems...

On Wed, Feb 20, 2013 at 12:34:12AM +0800, Daniel J Blueman wrote:
> Hi Paul,
> 
> On some of our larger servers with many hundreds of cores and when
> under high duress, we can see scheduler RCU stall warnings [1], so
> find we have to increase the hardcoded RCU_STALL_RAT_DELAY up from 2
> and RCU_JIFFIES_TILL_FORCE_QS up from 3.
> 
> Is there a more sustainable way to account for this to avoid it
> being hard-coded, such as making it and dependent timeouts a
> fraction of CONFIG_RCU_CPU_STALL_TIMEOUT?
> 
> On the other hand, perhaps this is just caused by clock jitter (eg
> due to distance from a contended clock source)? So increasing these
> a bit may just be adequate in general...

Hmmm...  What version of the kernel are you running?

							Thanx, Paul

> Many thanks,
>   Daniel
> 
> --- [1]
> 
> [ 3939.010085] INFO: rcu_sched detected stalls on CPUs/tasks: {}
> (detected by 1, t=29662 jiffies, g=3053, c=3052, q=598)
> [ 3939.020008] INFO: Stall ended before state dump start
> -- 
> Daniel J Blueman
> Principal Software Engineer, Numascale Asia
> 

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