linux-kernel - Re: [LKP] [rcu] 00f5159aeb6: +55.3% will-it-scale.time.involuntary_context

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Message-ID: <20150121085432.GD9719@linux.vnet.ibm.com>
Date:	Wed, 21 Jan 2015 00:54:32 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Huang Ying <ying.huang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, LKP ML <lkp@...org>
Subject: Re: [LKP] [rcu] 00f5159aeb6: +55.3%
 will-it-scale.time.involuntary_context_switches

On Wed, Jan 21, 2015 at 09:06:47AM +0100, Mike Galbraith wrote:
> On Tue, 2015-01-20 at 23:52 -0800, Paul E. McKenney wrote: 
> > On Wed, Jan 21, 2015 at 03:32:44PM +0800, Huang Ying wrote:
> > > FYI, we noticed the below changes on
> > > 
> > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git stall.2015.01.06a
> > > commit 00f5159aeb68f08ce29597be86be87d6db0c1ba1 ("rcu: Run grace-period kthreads at real-time priority")
> > 
> > Glad this helps!
> 
> The way I read it, it's hurting by increasing context switches... but if
> you'll need a boot param to turn it on in the future, this is moot :)

Heh!  I guess I should read it more carefully.  Anyway, the commit does
help in some heavy-load situations, but something more deft is clearly
required if it is to be enabled more generally.

							Thanx, Paul

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