linux-kernel - Re: [patch v4 01/18] sched: set SD_PREFER_SIBLING on MC domain to reduce a domain level

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Date:	Tue, 12 Feb 2013 11:11:19 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	torvalds@...ux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v4 01/18] sched: set SD_PREFER_SIBLING on MC domain to
 reduce a domain level

On Thu, 2013-01-24 at 11:06 +0800, Alex Shi wrote:
> The domain flag SD_PREFER_SIBLING was set both on MC and CPU domain at
> frist commit b5d978e0c7e79a, and was removed uncarefully when clear up
> obsolete power scheduler. Then commit 6956dc568 recover the flag on CPU
> domain only. It works, but it introduces a extra domain level since this
> cause MC/CPU different.
> 
> So, recover the the flag in MC domain too to remove a domain level in
> x86 platform.

This fails to clearly state why its desirable.. I'm guessing its because
we should use sibling cache domains before sibling threads, right?

A clearly stated reason is always preferable over: it was this way, make
it so again; which leaves us wondering why. 

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