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Subject: Re: Intel P6 vs P7 system call performance
From: Terje Eggestad <terje.eggestad@scali.com>
To: "J.A. Magallon" <jamagallon@able.es>
Cc: Mark Mielke <mark@mark.mielke.cc>, "H. Peter Anvin" <hpa@zytor.com>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Dave Jones <davej@codemonkey.org.uk>
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On tor, 2002-12-12 at 21:56, J.A. Magallon wrote:
> On 2002.12.12 Mark Mielke wrote:
> >On Thu, Dec 12, 2002 at 10:42:56AM +0100, Terje Eggestad wrote:
> >> On ons, 2002-12-11 at 19:50, H. Peter Anvin wrote:
> >> > Terje Eggestad wrote:
> >> > > PS:  rdtsc on P4 is also painfully slow!!!
> >> > Now that's just braindead...
> >> It takes about 11 cycles on athlon, 34 on PII, and a whooping 84 on P4.
> >> For a simple op like that, even 11 is a lot... Really makes you wonder.
> >
> >Some of this discussion is a little bit unfair. My understanding of what
> >Intel has done with the P4, is create an architecture that allows for
> >higher clock rates. Sure the P4 might take 84, vs PII 34, but how many
> >PII 2.4 Ghz machines have you ever seen on the market?
> >
> >Certainly, some of their decisions seem to be a little odd on the surface.
> >
> >That doesn't mean the situation is black and white.
> >
> 
> No. The situation is just black. Each day Intel processors are a bigger
> pile of crap and less intelligent, but MHz compensate for the average
> office user. Think of what could a P4 do if the same effort put on
> Hz was put on getting cheap a cache of 4Mb or 8Mb like MIPSes have. Or
> closer, 1Mb like G4s.
> If syscalls take 300% time but processor is also 300% faster 'nobody
> notices'.
  
Well, it does make sense if Intel optimized away rdtsc for more commonly
used things, but even that don't seem to be the case. I'm measuring the
overhead of doing a syscall on Linux (int 80) to be ~280 cycles on PIII,
and Athlon, while it's 1600 cycles on P4.

TJ


 
-- 
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Terje Eggestad                  mailto:terje.eggestad@scali.no
Scali Scalable Linux Systems    http://www.scali.com

Olaf Helsets Vei 6              tel:    +47 22 62 89 61 (OFFICE)
P.O.Box 150, Oppsal                     +47 975 31 574  (MOBILE)
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