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From: jbarnes@sgi.com (Jesse Barnes)
To: Tim Hockin <thockin@hockin.org>
Cc: Andi Kleen <ak@suse.de>, linux-kernel@vger.kernel.org
Subject: Re: Memory mapped IO vs Port IO
Date: Fri, 12 Sep 2003 11:24:30 -0700	[thread overview]
Message-ID: <20030912182430.GA1043@sgi.com> (raw)
In-Reply-To: <20030912111148.A15308@hockin.org>

On Fri, Sep 12, 2003 at 11:11:48AM -0700, Tim Hockin wrote:
> On Fri, Sep 12, 2003 at 08:00:03PM +0200, Andi Kleen wrote:
> > jbarnes@sgi.com (Jesse Barnes) writes:
> > 
> > > Ok, Andi asked for benchmarks, so I ran some.  Let this should be a
> > > lesson on why you shouldn't use port I/O :)  I ran these on an SGI Altix
> > > w/900 MHz McKinley processors.
> > > 
> > > Just straight calls to the routines (all of these are based on the
> > > average of 100 iterations):
> > >   writeq(val, reg) time: 64 cycles
> > >   outl(val, reg) time: 2126 cycles
> >                          ^^^^^
> > > 
> > > A simple branch:
> > >   if (use_mmio)
> > > 	writeq(val, reg) time: 132 cycles
> > >   else
> > > 	outl(val, reg) time: 1990 cycles
> >                              ^^^^^
> > Something seems to be wrong in your numbers.
> > 
> > Surely the outl in the if () cannot be faster than the pure outl() ?
> 
> Also - a perhaps more useful test is a write followed by a read.

Well, someone else will have to run that test.  On Altix, a read() is
freakishly expensive, and I'm not really interested in showing everyone
how bad it is ;)

Jesse

  reply	other threads:[~2003-09-12 18:28 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20030911192550.7dfaf08c.ak@suse.de.suse.lists.linux.kernel>
     [not found] ` <1063308053.4430.37.camel@huykhoi.suse.lists.linux.kernel>
     [not found]   ` <20030912162713.GA4852@sgi.com.suse.lists.linux.kernel>
     [not found]     ` <20030912174807.GA629@sgi.com.suse.lists.linux.kernel>
2003-09-12 18:00       ` Memory mapped IO vs Port IO Andi Kleen
2003-09-12 18:04         ` Jesse Barnes
2003-09-12 18:09           ` Andi Kleen
2003-09-12 18:11         ` Tim Hockin
2003-09-12 18:24           ` Jesse Barnes [this message]
2003-09-12 18:29             ` Andi Kleen
2003-09-12 18:58             ` Martin J. Bligh
2003-09-12 19:51               ` Jesse Barnes
2003-09-12 16:41 John Bradford
2003-09-12 21:52 ` Mike Fedyk
2003-09-13  4:01   ` Mike Fedyk
     [not found] <20030911160116.GI21596@parcelfarce.linux.theplanet.co.uk.suse.lists.linux.kernel>
2003-09-11 16:17 ` Andi Kleen
2003-09-11 16:25   ` Matthew Wilcox
2003-09-11 16:31     ` Andi Kleen
2003-09-11 16:42       ` Matthew Wilcox
2003-09-11 17:12       ` Jamie Lokier
2003-09-11 17:25         ` Andi Kleen
2003-09-12  1:39           ` jw schultz
2003-09-12 16:10           ` Anthony Dominic Truong
2003-09-12 16:22             ` Jamie Lokier
2003-09-12 16:27             ` Jesse Barnes
2003-09-12 17:48               ` Jesse Barnes
2003-09-11 17:13   ` Jamie Lokier
     [not found] ` <20030911161450.GA23536@sgi.com.suse.lists.linux.kernel>
2003-09-11 16:20   ` Andi Kleen
  -- strict thread matches above, loose matches on Subject: below --
2003-09-11 16:01 Matthew Wilcox
2003-09-11 16:14 ` Måns Rullgård
2003-09-11 16:14 ` Jesse Barnes

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