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

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Message-ID: <1259928516.17907.160.camel@laptop>
Date:	Fri, 04 Dec 2009 13:08:36 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Suresh Jayaraman <sjayaraman@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] sched: fix GENTLE_FAIR_SLEEPERS dependency

On Fri, 2009-12-04 at 17:12 +0530, Suresh Jayaraman wrote:
> On 12/04/2009 04:38 PM, Peter Zijlstra wrote:
> > On Fri, 2009-12-04 at 15:50 +0530, Suresh Jayaraman wrote:
> >>
> >> 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. 
> > 
> > This is really not meant to be used in that context. Its purely a debug
> > feature, with knobs coming and going as we see fit.
> > 
> 
> Does this also mean these features should not impact any specific
> workload much?

How would that follow?

> http://osdir.com/ml/linux-kernel/2009-09/msg03406.html
> In the thread above Ingo mentions about a few features and my
> understanding is that some of these might favour one type of workload
> than other. Is this not true anymore?

Sure it is, everything is workload dependent, the posix SCHED_OTHER task
model just doesn't include much usable information.

But that does not justify promoting this to generic tunable. What if you
happen to want to run two different workloads on one machine?

Its a CONFIG_SCHED_DEBUG thing, its in /debug (i've got a patch lined up
to remove the sysctl interface already), and I'm not going to guarantee
any kind of stability in the feature set what so ever.

Furthermore, if your favourite workload doesn't work well, file a bug
report (preferably with reproducer, otherwise its pure guesswork).

The only reason to poke at it is debugging, full stop, no whining or .33
won't have the interface anymore, which would be sad because then
everybody will have to recompile their kernel to debug things.

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