linux-kernel - Re: [PATCH] sched: make update_sd_pick

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Date:	Fri, 25 Jul 2014 19:57:47 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Michael Neuling <mikey@...ling.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	jhladky@...hat.com, ktkhai@...allels.com,
	tim.c.chen@...ux.intel.com,
	Nicolas Pitre <nicolas.pitre@...aro.org>
Subject: Re: [PATCH] sched: make update_sd_pick_busiest return true on a
 busier sd

On 25 July 2014 18:22, Rik van Riel <riel@...hat.com> wrote:
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>
> On 07/25/2014 12:05 PM, Peter Zijlstra wrote:
>> On Fri, Jul 25, 2014 at 11:45:02AM -0400, Rik van Riel wrote:
>>>> So for !ASYM the code is effectively:
>>>>
>>>> return sgs->avg_load > sds->busiest_stat.avg_load;
>>>>
>>>> I'd like to at least add a clause that makes overloaded groups
>>>>  prioritized over !overloaded groups.
>>>>
>>>> Also, like we found earlier, calculate_imbalance() relies on
>>>> the sum_nr_running > group_capacity_factor thing, which you've
>>>> just 'wrecked', so we'd need an update to that part too.
>>>
>>> I guess that would mean update_sd_pick_busiest would look like
>>> this for the !ASYM case:
>>>
>>> 1) remembering whether busiest is overloaded
>>>
>>> 2) if (sgs->busiest_stat.overloaded && !sgs->overloaded) return
>>> false;
>>>
>>> 3) if (sgs->avg_load > sds->busiest_stat.avg_load) return true;
>>
>> Right. So the situation I was worried about is where we have say 8
>> +nice tasks in one group and 2 -nice in another. So the group with
>> 2 tasks can actually be 'heavier' but not fully utilized. In that
>> case we want to pull tasks from the lighter but overloaded group.
>
> I can certainly create a new patch that makes update_sd_pick_busiest
> do just that.
>
> Vincent, any objections to me fixing update_sd_pick_busiest now, or
> will that conflict with your code cleanups?

It will probably conflict with my patchset which also modify
update_sd_pick_busiest but we should be able to manage the conflict.
So feel free to send a patch that fix the description above and we
will see how to handle the conflict when it will occur

Vincent

>
> - --
> All rights reversed
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