linux-kernel - Re: [PATCH 12/35] autonuma: CPU follow memory algorithm

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Date:	Tue, 29 May 2012 15:10:04 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 12/35] autonuma: CPU follow memory algorithm

On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:
> + * This function is responsible for deciding which is the best CPU
> + * each process should be running on according to the NUMA
> + * affinity. To do that it evaluates all CPUs and checks if there's
> + * any remote CPU where the current process has more NUMA affinity
> + * than with the current CPU, and where the process running on the
> + * remote CPU has less NUMA affinity than the current process to run
> + * on the remote CPU. Ideally this should be expanded to take all
> + * runnable processes into account but this is a good
> + * approximation. When we compare the NUMA affinity between the
> + * current and remote CPU we use the per-thread information if the
> + * remote CPU runs a thread of the same process that the current task
> + * belongs to, or the per-process information if the remote CPU runs
> a
> + * different process than the current one. If the remote CPU runs the
> + * idle task we require both the per-thread and per-process
> + * information to have more affinity with the remote CPU than with
> the
> + * current CPU for a migration to happen. 

This doesn't explain anything in the dense code that follows.

What statistics, how are they used, with what goal etc..


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