linux-kernel - Re: [PATCH, RFC] sched: update_top_cache_domain only at the times of building sched domain.

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Date:	Tue, 23 Jul 2013 22:20:20 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC] sched: update_top_cache_domain only at the times of
 building sched domain.

On Tue, Jul 23, 2013 at 10:09 PM, Rakib Mullick <rakib.mullick@...il.com> wrote:
> On Tue, Jul 23, 2013 at 9:47 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>> On Tue, Jul 23, 2013 at 09:44:17PM +0600, Rakib Mullick wrote:
>>>  Currently, update_top_cache_domain() is called whenever schedule domain is built or destroyed. But, the following
>>> callpath shows that they're at the same callpath and can be avoided update_top_cache_domain() while destroying schedule
>>> domain and update only at the times of building schedule domains.
>>>
>>>       partition_sched_domains()
>>>               detach_destroy_domain()
>>>                       cpu_attach_domain()
>>>                               update_top_cache_domain()
>>>               build_sched_domains()
>>>                       cpu_attach_domain()
>>>                               update_top_cache_domain()
>>>
>>
>> Does it really matter?
>
> Why should we do it twice? More importantly at the time of destroying
> even though we know it'll be built again just few moment later.
>
>>
>>
>> This just makes the code uglier for no gain afaict.
>>
>> If you really need to do this, key off @sd == NULL or something.
>
> Sorry, would you please a bit more clearer? I can't pick what you're suggesting.

You mean using sd == NULL rather than using update_cache_domain variable ?
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