Letter to DDJ

Andi Kleen ak@suse.de
Wed May 5 08:00:00 GMT 2004


Laurent GUERBY <laurent@guerby.net> writes:

> I believe you need to add a special instruction
> to prevent the hardware to reorder the execution of rdtsc

The P4 wont, but AMD CPUs will (especially K8).

> leading to wrong measurement, I don't remember what it was
> and the GCC asm for it though, may be someone else can help...

Before the RDTSC:

int tmp;
asm volatile("cpuid" : "=a" (tmp) : "0" (1) : "ebx","ecx","edx","memory")

-Andi



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