Re: Intel P6 vs P7 system call performance

Date: Mon Dec 09 2002 - 10:40:22 EST

Mike Hayward <> wrote:

> I have been benchmarking Pentium 4 boxes against my Pentium III laptop
> with the exact same kernel and executables as well as custom compiled
> kernels. The Pentium III has a much lower clock rate and I have
> noticed that system call performance (and hence io performance) is up
> to an order of magnitude higher on my Pentium III laptop. 1k block IO
> reads/writes are anemic on the Pentium 4, for example, so I'm trying
> to figure out why and thought someone might have an idea.
> Notice below that the System Call overhead is much higher on the
> Pentium 4 even though the cpu runs more than twice the speed and the
> system has DDRAM, a 400 Mhz FSB, etc. I even get pretty remarkable
> syscall/io performance on my Pentium III laptop vs. an otherwise idle
> dual Xeon.
> See how the performance is nearly opposite of what one would expect:
> M-Pentium III 850Mhz Sys Call Rate 433741.8
> Pentium 4 2Ghz Sys Call Rate 233637.8
> Xeon x 2 2.4Ghz Sys Call Rate 207684.2
...[other benchmark deleted]...
> Any ideas? Not sure I want to upgrade to the P7 architecture if this
> is right, since for me system calls are probably more important than
> raw cpu computational power.

You're assuming that ALL operations in a P4 are linearly faster than
a P-III. This is definitely not the case.

A P4 has a much longer pipeline (for a many cases, considerably
longer than the diagrams imply) than the P-III, and in particular
it has a much longer latency in handling mode transitions.

The results you got don't surprise me whatsoever. In fact the raw
system call transition instructions are likely 5x slower on the

    Erich Stefan Boleyn     <>
"Reality is truly stranger than fiction; Probably why fiction is so popular"
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