Re: [PATCH] sched: minor optimizations in wake_affine and select_task_rq_fair

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To: Chris Friesen <cfriesen@...>
Cc: <linux-kernel@...>, <vatsa@...>, <a.p.zijlstra@...>, <mingo@...>
Date: Tuesday, September 30, 2008 - 3:03 am

On Mon, Sep 29, 2008 at 10:09:41AM -0600, Chris Friesen wrote:

Thats a good question. Its kind of arguable and I wasn't sure if
everyone will be happy if I removed more arguments from wake_affine() than
what I did in my patch (because of the recalculations required).

wake_affine() currently has 11 arguments and I thought it may make sense
in reducing it to a sane number. For that I chose arguments which I
thought can be recalculated with minimum overhead (involves single struct
dereference, a simple per cpu variable and/or a simple arithmetic). And
one argument ("rq") which is being removed, isn't used at all in the
function!

Regarding the two variables you have mentioned, I didn't remove them as
args since I wasn't sure of "this_cpu" (which is nothing but
smp_processor_id()) as it is arch dependent, and calculating "prev_cpu"
involves two struct dereferences (((struct thread_info *)(task)->stack)->cpu).
And the calculation for other arguments (like, this_sd, load and this_load)
involves good amount of instructions.

If you disagree, what do you suggest we do here ?

Regards,
Amit Arora
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Re: [PATCH] sched: minor optimizations in wake_affine and se..., Amit K. Arora, (Tue Sep 30, 3:03 am)