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Date: Wed, 11 Dec 2002 10:50:57 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
Organization: Zytor Communications
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To: Terje Eggestad <terje.eggestad@scali.com>
CC: linux-kernel <linux-kernel@vger.kernel.org>,
       Dave Jones <davej@codemonkey.org.uk>
Subject: Re: Intel P6 vs P7 system call performance
References: <1039610907.25187.190.camel@pc-16.office.scali.no>
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Terje Eggestad wrote:
> 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.


Linus talked about this once, and it was agreed that the only sane way
to do this properly was via vsyscalls... have a page mapped somewhere in
high (kernel-area) memory, say at 0xfffff000, but readable by normal
processes.  A system call can be invoked via call 0xfffff000, and the
*kernel* enters whatever code is appropriate to enter itself.

> 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. 
> 

Yes.

> 
> PS:  rdtsc on P4 is also painfully slow!!!
> 

Now that's just braindead...

	-hpa


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