Re: [RFC][PATCH] sched: fix GENTLE_FAIR_SLEEPERS dependency

Suresh Jayaraman
2009-12-04T10:20:09Z

On 12/04/2009 03:24 PM, Ingo Molnar wrote:
>
> * Suresh Jayaraman <sjayaraman@suse.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