linux-kernel - Re: [RFT/PATCH v2 2/6] x86-64: Optimize vread

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Message-ID: <20110407225208.GD21838@one.firstfloor.org>
Date:	Fri, 8 Apr 2011 00:52:08 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Raghavendra D Prabhu <rprabhu@...hang.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andy Lutomirski <luto@....edu>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [RFT/PATCH v2 2/6] x86-64: Optimize vread_tsc's barriers

> 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@...ux.intel.com -- Speaking for myself only.
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