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Re: i386 lazy pmap switching in trap.c

On Sun, Feb 10, 2008 at 01:39:09AM +0900, YAMAMOTO Takashi wrote:
> > The decrement on exit would be cheaper than the loop around pmap_load.
> > (I've just got a measurable performance gain from removing the loop.)
> what exactly do you mean by "removing the loop"?


Although I'd also put a 'cmp' and 'jz' after the call earlier, which
is likely to be benefitialon athlons, but not P4 - which will predict
the backwards jump as taken if the branch isn't in the branch cache.

My guess is that copyin will almost always have the pmap loaded,
copyout probably more often than not.


David Laight: david%l8s.co.uk@localhost

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