Re: Intel P6 vs P7 system call performance

From: Linus Torvalds (
Date: Mon Dec 09 2002 - 12:48:45 EST

In article <>,
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.

P4's really suck at system calls. A 2.8GHz P4 does a simple system call
a lot _slower_ than a 500MHz PIII.

The P4 has problems with some other things too, but the "int + iret"
instruction combination is absolutely the worst I've seen. A 1.2GHz
Athlon will be 5-10 times faster than the fastest P4 on system call

HOWEVER, the P4 is really good at a lot of other things. On average, a
P4 tends to perform quite well on most loads, and hyperthreading (if you
have a Xeon or one of the newer desktop CPU's) also tends to work quite
well to smooth things out in real life.

In short: the P4 architecture excels at some things, and it sucks at
others. It _mostly_ tends to excel more than suck.

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This archive was generated by hypermail 2b29 : Sun Dec 15 2002 - 22:00:15 EST