Re: [patch] __volatile__ needed in get_cycles()?

Tigran Aivazian (tigran@sco.COM)
Mon, 29 Mar 1999 17:11:18 +0100 (BST)

On Mon, 29 Mar 1999, Richard Henderson wrote:
> Adding the volatile makes the asm act as a scheduling barrier.

Yes, but only on P5 (below P5 there is no rdtsc at all) architecture. Due
to the speculative execution of the P6 and above you will also need a
serializing instruction (e.g. cpuid) to make it a true "barrier".

Regards,
Tigran.

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