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SubjectRe: [RFC PATCH 4/4] x86/TSC: Use RDTSCP
On Wed, Dec 12, 2018 at 10:50:30AM -0800, Andy Lutomirski wrote:
> As far as I know, RDTSCP gets the job done, as does LFENCE, RDTSC on
> Intel.

Same on AMD when LFENCE has been made dispatch-serializing.

> There was a big discussion a few years ago where we changed it
> from LFENCE;RDTSC;LFENCE to just LFENCE;RDTSC after everyone was
> reasonably convinced that the uarch would not dispatch two RDTSCs
> backwards if the first one was immediately preceeded by LFENCE.

Yeah, the second one won't pass the LFENCE so you won't see time going
backwards, sure.


Good mailing practices for 400: avoid top-posting and trim the reply.

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