Re: Intel P6 vs P7 system call performance

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <20021209193649.GC10316@suse.de>
By author:    Dave Jones <davej@codemonkey.org.uk>
In newsgroup: linux.dev.kernel
>
> 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.

	-hpa

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