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From: Doug Ledford <dledford@redhat.com>
To: Kurt Garloff <garloff@suse.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: SMP spin-locks
Date: Fri, 15 Jun 2001 02:51:06 -0400	[thread overview]
Message-ID: <3B29B05A.38E89B02@redhat.com> (raw)
In-Reply-To: <Pine.LNX.3.95.1010614132506.10137B-100000@chaos.analogic.com> <20010614193501.F23383@garloff.etpnet.phys.tue.nl>

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

  reply	other threads:[~2001-06-15  2:44 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2001-06-14 17:26 Richard B. Johnson
2001-06-14 17:32 ` David S. Miller
2001-06-14 17:35 ` Kurt Garloff
2001-06-15  6:51   ` Doug Ledford [this message]
2001-06-14 20:42 ` Roger Larsson
2001-06-14 21:05   ` Richard B. Johnson
2001-06-14 21:30     ` Roger Larsson
2001-06-15  3:21       ` Richard B. Johnson
2001-06-15  2:33         ` David Lang
2001-06-15 10:35         ` David Schwartz
2001-06-15 13:26           ` Richard B. Johnson
2001-06-15 12:10     ` Ingo Oeser
2001-06-15 12:49       ` Richard B. Johnson
2001-06-15 15:52     ` Pavel Machek

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