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SubjectRe: [CFT][RFC] HT scheduler
On Sun, 14 Dec 2003, Nick Piggin wrote:

>
>
> bill davidsen wrote:
>
> >In article <3FDAB517.4000309@cyberone.com.au>,
> >Nick Piggin <piggin@cyberone.com.au> wrote:

> >Shared runqueues sound like a simplification to describe execution units
> >which have shared resourses and null cost of changing units. You can do
> >that by having a domain which behaved like that, but a shared runqueue
> >sounds better because it would eliminate the cost of even considering
> >moving a process from one sibling to another.
> >
>
> You are correct, however it would be a miniscule cost advantage,
> possibly outweighed by the shared lock, and overhead of more
> changing of CPUs (I'm sure there would be some cost).


> >| But if sched domains are accepted, there is no need for shared runqueues,
> >| because as I said they can do anything sched domains can, so the code would
> >| just be a redundant specialisation - unless you specifically wanted to share
> >| locks & data with siblings.
> >
> >I doubt the gain would be worth the complexity, but what do I know?
> >
>
> Sorry I didn't follow, gain and complexity of what?

Doing without shared runqueues is what I meant. A single runqueue appears
to avoid having to move processes between runqueues, or considering
*where* to move a process.

>
> Earlier in the thread Ingo thought my approach is simpler. code size is the
> same size, object size for my patch is significantly smaller, and it does
> more. Benchmarks have so far shown that my patch is as performant as shared
> runqueues.

If Ingo is happy, I am happy. I find shared runqueues very easy to
understand as a way to send tasks to a single HT chip, which is the only
case which comes to mind in which a CPU change is free. Clearly it isn't
going to apply to CPUs which don't share cache and behave more like
individual packages.

--
bill davidsen <davidsen@tmr.com>
CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

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