Re: Intel P6 vs P7 system call performance

Benjamin LaHaise (bcrl@redhat.com)
Tue, 17 Dec 2002 16:38:38 -0500

On Tue, Dec 17, 2002 at 10:57:29AM -0800, Ulrich Drepper wrote:
> But this is exactly what I expect to happen. If you want to implement
> gettimeofday() at user-level you need to modify the page. Some of the
> information the kernel has to keep for the thread group can be stored in
> this place and eventually be used by some uerlevel code executed by
> jumping to 0xfffff000 or whatever the address is.

You don't actually need to modify the page, rather the data for the user
level gettimeofday needs to be in a shared page and some register (like
%tr) must expose the current cpu number to index into the data. Either
way, it's an internal implementation detail for the kernel to take care
of, with multiple potential solutions.

-ben

-- 
"Do you seek knowledge in time travel?"
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