linux-kernel - Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs unpinnede

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Date:	Mon, 19 Sep 2011 22:05:28 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Paul Turner <pjt@...gle.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelianov <xemul@...allels.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs
 unpinnede

* Peter Zijlstra <a.p.zijlstra@...llo.nl> [2011-09-16 10:28:40]:

> > I think more compelling here is that it looks like nohz load-balance 
> > needs more love.
> 
> Quite probable,

Staring at nohz load-balancer for sometime, I see a potential issue:

'first_pick_cpu' and 'second_pick_cpu' can be idle without stopping
ticks for quite a while. When that happens, they stop bothering to
kick ilb cpu because of this snippet in nohz_kick_needed():

   static inline int nohz_kick_needed(struct rq *rq, int cpu)
   {

	..

        if (rq->idle_at_tick)
                return 0;

	..

   }


?

- vatsa
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