On Fri, Jun 05, 2015 at 09:09:26AM +0200, Hans Petter Selasky wrote:
> I was going through some timer code and found some unnecessary while
> loops in kern/kern_clocksource.c .
> I added some prints and found that during boot, "runs" can exceed 2000,
> while during regular usage runs is typically 1. Do you think it is worth
> to convert these loops into division and multiplications? It might make
> the CPU pipeline a tiny bit faster, having to skip some conditionals?
> And also possibly improve readability?
For typical loop count of one, I think that setup time for the division is
much greater than single substraction and non-taken conditional jump, which
is also should be consistently predicted as not taken.
You could try to run a microbenchmark to see if the patch makes any sense.
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