Re: Intel P6 vs P7 system call performance

From: H. Peter Anvin (
Date: Mon Dec 09 2002 - 14:46:47 EST

Followup to: <>
By author: Dave Jones <>
In newsgroup:
> On Mon, Dec 09, 2002 at 05:48:45PM +0000, Linus Torvalds wrote:
> > 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
> > overhead.
> Time to look into an alternative like SYSCALL perhaps ?

SYSCALL is AMD. SYSENTER is Intel, and is likely to be significantly
faster. Unfortunately SYSENTER is also extremely braindamaged, in
that it destroys *both* the EIP and the ESP beyond recovery, and
because it's allowed in V86 and 16-bit modes (where it will cause
permanent data loss) which means that it needs to be able to be turned
off for things like DOSEMU and WINE to work correctly.


<> at work, <> in private!
"Unix gives you enough rope to shoot yourself in the foot."	<>
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