Re: Intel P6 vs P7 system call performance

Benjamin LaHaise
2002-12-17T21:45:40Z

On Tue, Dec 17, 2002 at 01:41:55PM -0800, H. Peter Anvin wrote:
> > No, just take the number of context switches before and after the attempt
> > to read the time of day.

> How do you do that from userspace, atomically? A counter in the shared
> page?

Yup. You need some shared data for the TSC offset such anyways, so
moving the context switch counter onto such a page won't be much of
a problem. Using the %tr trick to get the CPU number would allow for
some of these data structures to be per-cpu without incurring any LOCK
overhead, too.

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