Re: Intel P6 vs P7 system call performance

[Martin J. Bligh]

>> It's not as good as a pure user-mode solution using tsc could be, but
>> we've seen the kinds of complexities that has with multi-CPU systems, and
>> they are so painful that I suspect the sysenter approach is a lot more
>> palatable even if it doesn't allow for the absolute best theoretical
>> numbers.
> 
> The complexity only applies to nonsynchronized TSCs though, I would
> assume.  I believe x86-64 uses a vsyscall using the TSC when it can
> provide synchronized TSCs, and if it can't it puts a normal system call
> inside the vsyscall in question.

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).

M.