Re: Intel P6 vs P7 system call performance

[James H. Cloos Jr.]

Linus> The system call entry becomes a simple

Linus> 	call *%gs:constant-offset

Linus> Not mmap. No magic system calls. No relinking. Not
Linus> _nothing_. One instruction, that's it.

I presume *%gs:0x18 is only for shared objects?

A naïve:

-               asm volatile("call 0xffffe000"
+               asm volatile("call *%%gs:0x18"

in the trivial getppid benchmark code gives a SEGV, since
(according to gdb's info all-registers) %gs == 0 when it runs.

Is it just that my glibc is too old, or is there a shared vs static difference?

-JimC

P.S.    On a (1 Gig) mobile p3 the getppid bench gives ~333 cycles for
        int $0x80 and ~215 for call 0xffffe000, before yesterday's push.