linux-kernel - Re: [ANNOUNCE] RSDL completely fair starvation free interactive cpu scheduler

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Date:	Mon, 12 Mar 2007 17:14:24 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	ck list <ck@....kolivas.org>, linux-kernel@...r.kernel.org
Subject: Re: [ANNOUNCE] RSDL completely fair starvation free interactive cpu scheduler

Con Kolivas wrote:
> > > The higher priority one always get 6-7ms whereas the lower priority
> > > one runs 6-7ms and then one larger perfectly bound expiration amount.
> > > Basically exactly as I'd expect. The higher priority task gets
> > > precisely RR_INTERVAL maximum latency whereas the lower priority task
> > > gets RR_INTERVAL min and full expiration (according to the virtual
> > > deadline) as a maximum. That's exactly how I intend it to work. Yes I
> > > realise that the max latency ends up being longer intermittently on
> > > the niced task but that's -in my opinion- perfectly fine as a
> > > compromise to ensure the nice 0 one always gets low latency.
> >
> > I think, it should be possible to spread this max expiration latency
> > across the rotation, should it not?
>
> There is a way that I toyed with of creating maps of slots to use for each
> different priority, but it broke the O(1) nature of the virtual deadline
> management. Minimising algorithmic complexity seemed more important to
> maintain than getting slightly better latency spreads for niced tasks. It
> also appeared to be less cache friendly in design. I could certainly try
> and implement it but how much importance are we to place on latency of
> niced tasks? Are you aware of any usage scenario where latency sensitive
> tasks are ever significantly niced in the real world?

It only takes one negatively nice'd proc to affect X adversely.


Thanks!

--
Al

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