Re: Intel P6 vs P7 system call performance

H. Peter Anvin
2002-12-19T22:31:56Z

Pavel Machek wrote:
> Hi!
>
>
>>>User on cpu1 reads time, communicates it to cpu2, but cpu2 is drifted
>>>-50ns, so it reads time "before" time reported cpu1. And gets confused.
>>>
>>
>>How can you get that communication to happen in < 50 ns?
>
>
> I'm not sure I can do that, but I'm not sure I can't either. CPUs
> snoop each other's cache, and that's supposed to be fast...
>

Even over a 400 MHz FSB you have 2.5 ns cycles. I doubt you can
transfer a cache line in 20 FSB cycles.

-hpa