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Date: Mon, 19 Sep 2011 22:05:28 +0530
From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Turner <pjt@google.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Bharata B Rao <bharata@linux.vnet.ibm.com>,
        Dhaval Giani <dhaval.giani@gmail.com>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@elte.hu>, Pavel Emelianov <xemul@parallels.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs
 unpinnede
Message-ID: <20110919163528.GC21064@linux.vnet.ibm.com>
Reply-To: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
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* Peter Zijlstra <a.p.zijlstra@chello.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