Messages in this thread | | | Subject | Re: Intel P6 vs P7 system call performance | From | Terje Eggestad <> | Date | 11 Dec 2002 13:48:27 +0100 |
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It get even worse with Hammer. When you run hammer in compatibility mode (32 bit app on a 64 bit OS) the sysenter is an illegal instruction. Since Intel don't implement syscall, there is no portable sys* instruction for 32 bit apps. You could argue that libc hides it for you and you just need libc to test the host at startup (do I get a sigill if I try to do getpid() with sysenter? syscall? if so we uses int80 for syscalls). But not all programs are linked dyn.
Too bad really, I tried the sysenter patch once, and the gain (on PIII and athlon) was significant.
Fortunately the 64bit libc for hammer uses syscall.
PS: rdtsc on P4 is also painfully slow!!!
TJ
On man, 2002-12-09 at 20:46, H. Peter Anvin wrote: > 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
-- _________________________________________________________________________
Terje Eggestad mailto:terje.eggestad@scali.no Scali Scalable Linux Systems http://www.scali.com
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