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SubjectRe: [PATCH v2] sched: Accelerate "pick_next_entity" under special condition

* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> On Tue, 2012-01-17 at 11:04 +0800, Michael Wang wrote:
> >
> > > Then what if condition 1 is true now?
> >
> > We can see in original code, even condition 1 is true, we
> > still will use value3 if condition3 is true, like this:
> >
> > original:
> >
> > condition1 condition3 result
> > true true value3
> > true false value1
> >
> > That means if condition3 is true, we don't care whether
> > condition1 is true or not because we will finally use value3.
>
> Right, so from the original 8 possible states we used to evaluate 3*8 =
> 24 conditionals. The new code will reduce this to 1*4 + 2*2 + 2*3 = 14.
>
> Now I guess the question is if it matters for the modal or average
> state.
>
> I've applied the patch since it can't be worse, but I've no idea if it
> matters or not in practice.

A before/after kernel/sched.o size comparison on 64-bit
defconfig typically gives a pretty good indication whether it's
a step forward or not.

Thanks,

Ingo


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