Re: Large increase in context switch rate

From: Jeremy Fitzhardinge
Date: Thu Jul 17 2008 - 12:11:35 EST

(Don't top-post.)

Alex Nixon (Intern) wrote:
I'm talking about total number of context switches - kernbench gets it

time -f "%c" make -j 4

Dividing through it gives me a rate of around 250/sec (vs Peters 3000),
but I've set CONFIG_HZ=100 (vs Peters 1000), so they don't wildly

Well spotted :-)

OK, but that still doesn't account for the relatively large increase from 2.6.18 -> 2.6.26. You're using HZ=100 in both cases, I presume.

The other variable is NOHZ and highres timers. You could try turning those off in 2.6.26. Also, CONFIG_PREEMPT could well make a difference. 2.6.18-xen doesn't support CONFIG_PREEMPT at all, but pvops(-xen) does.

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