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SubjectRe: [report] renicing X, cfs-v5 vs sd-0.46


On Mon, 23 Apr 2007, Ingo Molnar wrote:
>
> You are completely right in the case of traditional schedulers.

And apparently I'm completely right with CFS too.

> Using CFS-v5, with Xorg at nice 0, the context-switch rate is low:
>
> procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
> r b swpd free buff cache si so bi bo in cs us sy id wa st
> 2 0 0 472132 13712 178604 0 0 0 32 113 170 83 17 0 0 0
> 2 0 0 472172 13712 178604 0 0 0 0 112 184 85 15 0 0 0
> 2 0 0 472196 13712 178604 0 0 0 0 108 162 83 17 0 0 0
> 1 0 0 472076 13712 178604 0 0 0 0 115 189 86 14 0 0 0

Around 170 context switches per second.

> Renicing X to -10 increases context-switching, but not dramatically so,
> because it is throttled by CFS:
>
> procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
> r b swpd free buff cache si so bi bo in cs us sy id wa st
> 4 0 0 475752 13492 176320 0 0 0 64 116 1498 85 15 0 0 0
> 4 0 0 475752 13492 176320 0 0 0 0 107 1488 84 16 0 0 0
> 4 0 0 475752 13492 176320 0 0 0 0 140 1514 86 14 0 0 0
> 4 0 0 475752 13492 176320 0 0 0 0 107 1477 85 15 0 0 0
> 4 0 0 475752 13492 176320 0 0 0 0 122 1498 84 16 0 0 0

Did you even *look* at your own numbers? Maybe you looked at "interrpts".
The context switch numbers go from 170 per second, to 1500 per second!

If that's not "dramatically so", I don't know what is! Just how many
orders of magnitude worse does it have to be, to be "dramatic"? Apparently
one order of magnitude isn't "dramatic"?

So you were wrong. The fact that it was still "usable" is a good
indication, but how about just admitting that you were wrong, and that
renicing X is the *WRONG*THING*TO*DO*.

Just don't do it. It's wrong. It was wrong with the old schedulers, it's
wrong with the new scheduler, it's just WRONG.

It was a hack, and it's a failed hack. And the fact that you don't seem to
realize that it's a failure, even when your OWN numbers clearly show that
it's failed, is a bit scary.

Linus
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