Re: Intel P6 vs P7 system call performance

[H. Peter Anvin]

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