Re: Intel P6 vs P7 system call performance

H. Peter Anvin
2002-12-17T20:09:15Z

Alan Cox wrote:
> On Tue, 2002-12-17 at 19:26, Martin J. Bligh wrote:
>
>>>>It's not as good as a pure user-mode solution using tsc could be, but
>>
>>You can't use the TSC to do gettimeofday on boxes where they aren't
>>syncronised anyway though. That's nothing to do with vsyscalls, you just
>>need a different time source (eg the legacy stuff or HPET/cyclone).
>
>
> Ditto all the laptops and the like. With code provided by the kernel we
> can cheat however. If we know the fastest the CPU can go (ie full speed
> on spudstop/powernow etc) we can tell the tsc value at which we have to
> query the kernel to get time to any given accuracy, so allowing limited
> caching
>
> Ditto by knowing the worst case drift on summit
>

Clever. I like it :)

-hpa