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Date: Thu, 26 Jan 2012 12:26:36 +0100
From: Jens Axboe <axboe@kernel.dk>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
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        Ingo Molnar <mingo@elte.hu>, Arjan van de Ven <arjan@linux.intel.com>,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v1 1/2] sched: unified sched_powersavings sysfs tunable
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On 01/26/2012 12:08 PM, Peter Zijlstra wrote:
> On Thu, 2012-01-26 at 11:42 +0100, Jens Axboe wrote:
>> On 01/25/2012 03:53 PM, Peter Zijlstra wrote:
> 
>>> Jens, what is this thing trying to do?
>>
>> The intent of the code
>> is to return the first CPU in the "group" that the passed in core/thread
>> belongs to. This is used to decide whether to perform a completion
>> locally, or to send it off to a different "group".
> 
> Would you perhaps have meant to identify some shared cache domain?
> 
> In the scheduler core code we have (for CONFIG_SMP):
> 
>   static int ttwu_share_cache(int this_cpu, int that_cpu);
> 
> which returns true if this and that share a cache and false otherwise.
> Would that suffice or do you need a slightly different form? That is, we
> should provide you with some API and avoid you having to poke around
> with CONFIG_SCHED* and topology bits methinks.

Yeah, I think that would suit my purpose nicely, in fact. What level of
cache sharing is being used here? The block code wanted a per-socket
type operation, but since it's a heuristic, perhaps the above is even
better (or equivelant, perhaps).

-- 
Jens Axboe