Messages in this thread | | | Subject | Re: Intel P6 vs P7 system call performance | From | Alan Cox <> | Date | 17 Dec 2002 20:51:11 +0000 |
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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
Alan
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