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

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Date:	Fri, 25 Jul 2014 12:22:47 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, mikey@...ling.org, mingo@...nel.org,
	pjt@...gle.com, jhladky@...hat.com, ktkhai@...allels.com,
	tim.c.chen@...ux.intel.com, nicolas.pitre@...aro.org,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] sched: make update_sd_pick_busiest return true on a busier
 sd

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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?

- -- 
All rights reversed
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