Re: Can context switches be faster?

Jeremy Fitzhardinge
2006-10-12T20:33:21Z

John Richard Moser wrote:
> That's a load more descriptive :D
>
> 0.890 uS, 0.556uS/cycle, that's barely 2 cycles you know. (Pentium M)
> PPC performs similarly, 1 cycle should be about 1uS.
>

No, you're a factor of 1000 off - these numbers show the context switch
is around 1600-75000 cycles. And that doesn't really tell the whole
story: if caches/TLB get flushed on context switch, then the newly
switched-to task will bear the cost of having cold caches, which isn't
visible in the raw context switch time.

But modern x86 processors have a very quick context switch time, and I
don't think there's much room for improvement aside from
micro-optimisations (though that might change if the architecture grows
a way to avoid flushing the TLB on switch).

J