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Date: Mon, 11 Nov 2013 08:39:45 -0800
From: Arjan van de Ven <arjan@linux.intel.com>
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To: Peter Zijlstra <peterz@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>
CC: Vincent Guittot <vincent.guittot@linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Paul Turner <pjt@google.com>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
        Chris Metcalf <cmetcalf@tilera.com>, Tony Luck <tony.luck@intel.com>,
        "alex.shi@intel.com" <alex.shi@intel.com>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
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        Paul McKenney <paulmck@linux.vnet.ibm.com>, linux-pm@vger.kernel.org
Subject: Re: [RFC][PATCH v5 00/14] sched: packing tasks
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> I think the scheduler simply wants to say: we expect to go idle for X
> ns, we want a guaranteed wakeup latency of Y ns -- go do your thing.

as long as Y normally is "large" or "infinity" that is ok ;-)
(a smaller Y will increase power consumption and decrease system performance)



> I think you also raised the point in that we do want some feedback as to
> the cost of waking up particular cores to better make decisions on which
> to wake. That is indeed so.

having a hardware driver give a prefered CPU ordering for wakes can indeed be useful.
(I'm doubtful that changing the recommendation for each idle is going to pay off,
but proof is in the pudding; there are certainly long term effects where this can help)

>