linux-kernel - Re: [RFC][PATCH 25/26] sched, numa: Only migrate long-running entities

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Date:	Sun, 08 Jul 2012 14:34:05 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	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>,
	Dan Smith <danms@...ibm.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 25/26] sched, numa: Only migrate long-running entities

On 03/16/2012 10:40 AM, Peter Zijlstra wrote:

> +static u64 process_cpu_runtime(struct numa_entity *ne)
> +{
> +	struct task_struct *p, *t;
> +	u64 runtime = 0;
> +
> +	rcu_read_lock();
> +	t = p = ne_owner(ne);
> +	if (p) do {
> +		runtime += t->se.sum_exec_runtime; // @#$#@ 32bit
> +	} while ((t = next_thread(t)) != p);
> +	rcu_read_unlock();
> +
> +	return runtime;
> +}

> +	/*
> +	 * Don't bother migrating memory if there's less than 1 second
> +	 * of runtime on the tasks.
> +	 */
> +	if (ne->nops->cpu_runtime(ne) < NSEC_PER_SEC)
> +		return false;

Do we really want to calculate the amount of CPU time used
by a process, and start migrating after just one second?

Or would it be ok to start migrating once a process has
been scanned once or twice by the NUMA code?

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