Re: [RFT/PATCH v2 2/6] x86-64: Optimize vread_tsc's barriers

[Andi Kleen]

> If only one lfence or serializing instruction is to be used, can't we
> just use RDTSCP instruction (X86_FEATURE_RDTSCP,available only in >=
> i7's and AMD)  which both provides TSC as well as an upward serializing

RDTSCP is a full synchronization, much heavier and slower than LFENCE
(or even two of them) Besides it doesn't exist on older CPUs.

-Andi
-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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