Re: SMP spin-locks

Doug Ledford
2001-06-15T02:44:47Z

Kurt Garloff wrote:
>
> On Thu, Jun 14, 2001 at 01:26:05PM -0400, Richard B. Johnson wrote:
> > Question 2: What is the purpose of the code sequence, "repz nop"
>
> Puts iP4 into low power mode.

Umm, slightly more accurate would be to say that it makes the P4 processor
wait before resuming the loop to give the lock a chance to have been
released. It makes the code go from a constant busy loop to a check/wait
small amount of time/check again loop. This in turns keeps your processor
from trying to constantly check the lock itself which is suppossed to have
benefits in terms of inter-processor bus pressure.

--

Doug Ledford <dledford@redhat.com> http://people.redhat.com/dledford
Please check my web site for aic7xxx updates/answers before
e-mailing me about problems