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SubjectRe: sched: context tracking demolishes pipe-test
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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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