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

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Message-ID: <CADZ9YHgdK86MuGk7QcsYt+pRZpJ7GYG-rUWf77p9jWZvkw+i5w@mail.gmail.com>
Date:	Tue, 23 Jul 2013 22:09:00 +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 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.
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