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From: Catalin Marinas <catalin.marinas@arm.com>
Date: Fri, 21 Jun 2013 22:23:25 +0100
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Subject: Re: power-efficient scheduling design
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>, David Lang <david@lang.hm>,
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On 21 June 2013 16:38, Arjan van de Ven <arjan@linux.intel.com> wrote:
> On 6/21/2013 1:50 AM, Morten Rasmussen wrote:
>> A hint when a task is moved to a new cpu is too late if the migration
>> shouldn't have happened at all. If the scheduler knows that the cpu is
>> able to switch to a higher p-state it can decide to wait for the p-state
>> change instead of migrating the task and waking up another cpu.
>
> oops sorry I misread your mail (lack of early coffee I suppose)
>
> I can see your point of having a thing for "did we ask for all the performance
> we could ask for" prior to doing a load balance (although, for power efficiency,
> if you have two tasks that could run in parallel, it's usually better to
> run them in parallel... so likely we should balance anyway)

Not necessarily, especially if parallel running implies powering up a
full cluster just for one CPU (it depends on the hardware but for
example a cluster may not be able to go in deeper sleep states unless
all the CPUs in that cluster are idle).

--
Catalin