Re: sched: context tracking demolishes pipe-test

[Mike Galbraith]

On Sun, 2013-06-30 at 23:29 +0200, Peter Zijlstra wrote:

> Yeah, who'd have thought that putting stuff in the syscall path would've
> made syscalls more expensive ;-)

(careful, you'll injure my innocence, Santa and the Tooth Fairy exist!)

> But yeah, that's a _lot_ more expensive.. I'd not be surprised if more
> people would find that objectionable.

Distros may want some hot patching or _something_ before doing the usual
new=turn-it-on thing.  Per trusty (spelled with 'c') old Q6600, the cost
is pretty darn high.

-regress is my ~light regression testing config, carried forward from
3.6.32...master across all intervening trees.
-regressx is plus CONFIG_RCU_USER_QS=y CONFIG_CONTEXT_TRACKING_FORCE=y
-regressxx is plus full dynticks 

taskset -c 3 pipe-test 1

2.6.32-regress    654.5 Khz            1.000
3.10.0-regress    652.1 Khz             .996     1.000
3.10.0-regressx   476.8 Khz             .728      .731
3.10.0-regressxx  275.6 Khz             .421      .422

tbench

2.6.32-regress    327.502 MB/sec       1.000
3.10.0-regress    319.621 MB/sec        .975     1.000
3.10.0-regressx   292.894 MB/sec        .894      .916
3.10.0-regressxx  243.738 MB/sec        .744      .762

netperf TCP_RR

2.6.32-regress   104041.84 Trans/sec   1.000
3.10.0-regress    94961.34 Trans/sec    .912     1.000
3.10.0-regressx   82383.33 Trans/sec    .791      .867
3.10.0-regressxx  61527.59 Trans/sec    .591      .647

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