Re: [PATCH v3] cpuidle: poll_state: Add time limit to poll_idle()

[Rik van Riel]

On Mon, 2018-03-26 at 23:44 +0200, Rafael J. Wysocki wrote:
> On Mon, Mar 26, 2018 at 6:32 PM, Rik van Riel <riel@xxxxxxxxxxx>
> wrote:
> > On Sun, 2018-03-25 at 23:34 +0200, Rafael J. Wysocki wrote:
> > 
> > I tried that, as well, and some other variations.
> > 
> > Every single change to poll_idle() that I tried
> > seems to result in a 9-10% relative increase in
> > CPU use during the peak load of the test.
> > 
> > During the busiest parts of the load, every CPU
> > sees on the order of 20k context switches a second.

... and I did something wrong in the tests :/

> Hmm.  Basically, you are saying that
> 
> while (something)
>     cpu_relax();
> 
> is measurably less overhead than
> 
> while (something) {
>     cpu_relax();
>     check something else;
>     cpu_relax();
> }
> 
> which honestly makes me wonder how this is possible at all.

Part of the mystery is solved. Apparently the
control kernel was not the one I thought it
was, or the one that was printed in the 
output messages :(

I am re-running the tests now with a few
variations, and seeing what works best.

My apologies for wasting everybody's time.

I should have valid results later tonight.
Fingers crossed.

-- 
All Rights Reversed.

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