linux-kernel - Re: [RFC][PATCH] sched: fix GENTLE_FAIR

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Date:	Fri, 04 Dec 2009 15:50:07 +0530
From:	Suresh Jayaraman <sjayaraman@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] sched: fix GENTLE_FAIR_SLEEPERS dependency

On 12/04/2009 03:24 PM, Ingo Molnar wrote:
> 
> * Suresh Jayaraman <sjayaraman@...e.de> wrote:
> 
>> The newly introduced GENTLE_FAIR_SLEEPERS does not seem to have any
>> effect without FAIR_SLEEPERS. Fix sysctl.sched_features to reflect
>> this. Without this change, a user who sets GENTLE_FAIR_SLEEPERS
>> without FAIR_SLEEPERS would assume gentle sleeper fairness which
>> is not guaranteed.
>>
> 
> There's a lot of other dependencies between scheduler features so it's 
> possible to change it without it having an effect on the scheduler. 
> 
> sched_features is really a development/debugging facility, you have to 
> know what you are doing.

I think originally introduced as a development/debugging facility,
sched_features is slowly transforming into a viable tool for System
Administrators, by looking at the impact of turning on/off some of these
features on some workloads (especially non-desktop workloads). And I
think these benefits should be passed on to the end users perhaps in the
form of documentation.

> Might be worth adding a comment to the feature definition place itself 
> in the source - explain what it does and how it makes sense (and how it 
> doesnt).
> 

Yes it make more sense to make such changes as part of documentation
than a code enforcement. I'll try and collect some of the useful tuning
information.


Thanks,

-- 
Suresh Jayaraman
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