Re: Linux timekeeping plans

Alan Cox (
Sun, 6 Dec 1998 17:36:22 +0000 (GMT)

> However, slow as it is, it's still the fastest inter-processor communication
> system I know of. Which is why it's used for spinlocks.
> (Do you know anything faster?)

You can map areas of memory non cached with the MTRR stuff on PPro and higher
if you wish, but the memory stuff is probably faster than using PCI space as a
target for measurement or interrupts

> Well, one thing a bit faster is doing the whole thing to write-through
> memory. (Does Linux have any write-through space it uses for such things?)

See the mtrr device - generally no.

> And yes, I do measure the time it takes to do this.
> The measured time from A->B is bus_time + skew.
> The measured time from B->A is bus_time - skew.
> Thus, bus_time = (abtime + batime)/2, and skew = (abtime - batime)/2).
> Thats how I measure.

That should compute it nicely. I can't see a problem with that at all


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