Re: Large increase in context switch rate

[Jeremy Fitzhardinge]

(Don't top-post.)

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

   J
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