Re: Intel P6 vs P7 system call performance

H. Peter Anvin
2002-12-17T21:33:23Z

Benjamin LaHaise wrote:
> 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.
>

That's not the problem... the problem is that the userland code can get
preempted at any time and rescheduled on another CPU.

-hpa