linux-kernel - Re: [RFC][PATCH v5 00/14] sched: packing tasks

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Date:	Mon, 11 Nov 2013 23:43:23 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Morten Rasmussen <Morten.Rasmussen@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Tony Luck <tony.luck@...el.com>,
	"alex.shi@...el.com" <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"l.majewski@...sung.com" <l.majewski@...sung.com>,
	Jonathan Corbet <corbet@....net>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [RFC][PATCH v5 00/14] sched: packing tasks

On 11 Nov 2013, at 19:26, Arjan van de Ven <arjan@...ux.intel.com> wrote:
> On 11/11/2013 10:31 AM, Catalin Marinas wrote:
>> I agree, we can't rely on the requested C-state but the_actual_  state
>> and this means querying the hardware driver. Can we abstract this via
>> some interface which provides the cost of waking up a CPU? This could
>> take into account the state of the other CPUs in the cluster and the
>> scheduler is simply concerned with the wake-up costs.
> 
> can you even query this without actually waking up the cpu and asking ???

Even if you don’t have additional hardware to query the state of a CPU
without waking it up, we could have a per-CPU variable storing the
actual C-states as selected by the arch backend.  This doesn’t need to
be precise but lets say only 90% accurate would probably be enough for
the scheduler.

Catalin--
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