From: peterz@infradead•org (Peter Zijlstra)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC PATCH v3 3/6] sched: pack small tasks
Date: Fri, 26 Apr 2013 12:18:49 +0200 [thread overview]
Message-ID: <20130426101849.GD8669@dyad.programming.kicks-ass.net> (raw)
In-Reply-To: <5152C83F.6060509@linux.vnet.ibm.com>
On Wed, Mar 27, 2013 at 03:51:51PM +0530, Preeti U Murthy wrote:
> Hi,
>
> On 03/26/2013 05:56 PM, Peter Zijlstra wrote:
> > On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote:
> >> +static bool is_buddy_busy(int cpu)
> >> +{
> >> + struct rq *rq = cpu_rq(cpu);
> >> +
> >> + /*
> >> + * A busy buddy is a CPU with a high load or a small load with
> >> a lot of
> >> + * running tasks.
> >> + */
> >> + return (rq->avg.runnable_avg_sum >
> >> + (rq->avg.runnable_avg_period / (rq->nr_running
> >> + 2)));
> >> +}
> >
> > Why does the comment talk about load but we don't see it in the
> > equation. Also, why does nr_running matter at all? I thought we'd
> > simply bother with utilization, if fully utilized we're done etc..
> >
>
> Peter, lets say the run-queue has 50% utilization and is running 2
> tasks. And we wish to find out if it is busy. We would compare this
> metric with the cpu power, which lets say is 100.
>
> rq->util * 100 < cpu_of(rq)->power.
>
> In the above scenario would we declare the cpu _not_busy? Or would we do
> the following:
>
> (rq->util * 100) * #nr_running < cpu_of(rq)->power and conclude that it
> is just enough _busy_ to not take on more processes?
That is just confused... ->power doesn't have anything to do with a per-cpu
measure. ->power is a inter-cpu measure of relative compute capacity.
Mixing in nr_running confuses things even more; it doesn't matter how many
tasks it takes to push utilization up to 100%; once its there the cpu simply
cannot run more.
So colour me properly confused..
next prev parent reply other threads:[~2013-04-26 10:18 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-22 12:25 [RFC PATCH v3 0/6] sched: packing small tasks Vincent Guittot
2013-03-22 12:25 ` [RFC PATCH v3 1/6] Revert "sched: Introduce temporary FAIR_GROUP_SCHED dependency for load-tracking" Vincent Guittot
2013-03-22 12:25 ` [RFC PATCH v3 2/6] sched: add a new SD_SHARE_POWERDOMAIN flag for sched_domain Vincent Guittot
2013-03-22 12:25 ` [RFC PATCH v3 3/6] sched: pack small tasks Vincent Guittot
2013-03-26 12:26 ` Peter Zijlstra
2013-03-27 10:21 ` Preeti U Murthy
2013-03-27 11:00 ` Vincent Guittot
2013-04-26 10:30 ` Peter Zijlstra
2013-04-26 11:34 ` Vincent Guittot
2013-04-26 10:18 ` Peter Zijlstra [this message]
2013-04-26 10:32 ` Preeti U Murthy
2013-03-26 12:37 ` Peter Zijlstra
2013-03-26 13:00 ` Vincent Guittot
2013-03-27 4:33 ` Preeti U Murthy
2013-03-27 4:48 ` Alex Shi
2013-03-27 8:51 ` Peter Zijlstra
2013-03-26 12:46 ` Peter Zijlstra
2013-03-26 13:53 ` Vincent Guittot
2013-03-26 15:29 ` Arjan van de Ven
2013-03-27 8:46 ` Peter Zijlstra
2013-03-27 8:54 ` Vincent Guittot
2013-03-27 9:00 ` Peter Zijlstra
2013-03-27 11:18 ` Catalin Marinas
2013-03-27 14:13 ` Peter Zijlstra
2013-03-27 16:36 ` Catalin Marinas
2013-03-27 17:18 ` Nicolas Pitre
2013-03-27 17:37 ` Catalin Marinas
2013-03-27 17:20 ` Vincent Guittot
2013-03-27 18:01 ` Catalin Marinas
2013-03-27 15:37 ` Nicolas Pitre
2013-03-22 12:25 ` [RFC PATCH v3 4/6] sched: secure access to other CPU statistics Vincent Guittot
2013-03-26 12:50 ` Peter Zijlstra
2013-03-26 13:06 ` Vincent Guittot
2013-03-22 12:25 ` [RFC PATCH v3 5/6] sched: pack the idle load balance Vincent Guittot
2013-03-26 12:52 ` Peter Zijlstra
2013-03-26 14:03 ` Vincent Guittot
2013-03-26 14:42 ` Peter Zijlstra
2013-03-26 15:55 ` Vincent Guittot
2013-03-27 4:56 ` Alex Shi
2013-03-27 8:05 ` Vincent Guittot
2013-03-27 8:47 ` Alex Shi
2013-03-27 10:30 ` Vincent Guittot
2013-03-27 13:32 ` Alex Shi
2013-03-27 8:49 ` Peter Zijlstra
2013-04-05 11:08 ` Vincent Guittot
2013-04-22 5:45 ` Preeti U Murthy
[not found] ` <CAKfTPtCCCifC=c+xjjnAH_HSqkR80PiQoddQKXPHuZwZawbvcA@mail.gmail.com>
2013-04-23 2:23 ` Alex Shi
2013-04-23 4:57 ` Preeti U Murthy
2013-04-23 15:30 ` Arjan van de Ven
2013-04-26 10:54 ` Peter Zijlstra
2013-04-23 4:36 ` Preeti U Murthy
2013-03-22 12:25 ` [RFC PATCH v3 6/6] ARM: sched: clear SD_SHARE_POWERDOMAIN Vincent Guittot
2013-03-23 11:55 ` [RFC PATCH v3 0/6] sched: packing small tasks Preeti U Murthy
2013-03-25 9:58 ` Vincent Guittot
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