Re: [PATCH] optional non-interactive mode for cpu scheduler

[Con Kolivas <kernel@kolivas.org>]

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Ingo Molnar wrote:
> * Con Kolivas <kernel@kolivas.org> wrote:
> 
> 
>>optional non-interactive mode for cpu scheduler
> 
> 
> i think the following scheme would work better:
> 
>  - introduce a new SCHED_CPUBOUND policy
>  - return ->static_prio + 5 for such tasks
>  - keep their timeslice based off ->static_prio
> 
> the point is this: such tasks would thus be automatically and
> perpetually considered 'CPU hogs'. Applications cannot abuse this
> mechanism because they get the maximum 'penalty'.
> 
> and as a bonus, no magic sysctl and inherently more flexibility.
> 
> (note that this scheme has advantages above nice +5 because nice +5
> still has the interactivity stuff on which can create priority
> fluctuations and may thus affect workloads.)
> 
> if you agree with this scheme, would you be interested in implementing
> this?

The better cpu proportion guarantee without low latency of such a policy 
would be desirable to video encoding in the background while capturing 
in the foreground as one immediately recognisable purpose, and there are 
likely numerous others, so I agree it's a good idea.

However the non-interactive mode addresses a number of different needs 
that seem to have come up. Specifically:
I have had users report great success with such a mode on my own 
scheduler in multiple X session setups where very choppy behaviour 
occurs in mainline.
Many high performance computing people do not wish interactivity code 
modifying their choice of latency/distribution - admittedly this is a 
soft one.

What are your thoughts on this?

Con

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