linux-kernel - Re: [PATCH v5 08/12] sched: move cfs task on a CPU with higher capacity

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Message-ID: <CAKfTPtA=rfM5VWF9On1SJUcNcTvYOBg-XVMcL8bY8LD2BjceYg@mail.gmail.com>
Date:	Fri, 5 Sep 2014 14:24:04 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	Rik van Riel <riel@...hat.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v5 08/12] sched: move cfs task on a CPU with higher capacity

On 5 September 2014 14:06, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote:
> Hi Vincent,
>
> On 08/26/2014 04:36 PM, Vincent Guittot wrote:
>> If the CPU is used for handling lot of IRQs, trig a load balance to check if
>> it's worth moving its tasks on another CPU that has more capacity.
>>
>> As a sidenote, this will note generate more spurious ilb because we already
>> trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that
>> has a task, we will trig the ilb once for migrating the task.
>>
>> The nohz_kick_needed function has been cleaned up a bit while adding the new
>> test
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>
> So I see that there are added checks in your previous patches on if the
> cpu capacity for CFS tasks is good enough to run tasks on the cpu. My
> concern is although they appear sensible, would they trigger an increase
> in the number of times we load balance to a large extent.
>
> Ebizzy would not test this aspect right? There are no real time
> tasks/interrupts that get generated.

yes, ebizzy doesn't test this part but check for non regression

The scp test is the one that i use to check this patch and the
previous one but a test with some cfs and rt tasks should also do the
jobs.
we can see an increase of 82% for the dual core when
CONFIG_IRQ_TIME_ACCOUNTING is enable

>
> Besides, what is the column that says patchset+irq? What is the irq
> accounting patchset that you refer to in your cover letter?

it refers to CONFIG_IRQ_TIME_ACCOUNTING which includes the time spent
under interrupt context to compute the scale_rt_capacity

Regards,
Vincent

>
> Regards
> Preeti U Murthy
>
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