Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757815AbYB2Kn7 (ORCPT ); Fri, 29 Feb 2008 05:43:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755297AbYB2Knv (ORCPT ); Fri, 29 Feb 2008 05:43:51 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:35808 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755261AbYB2Knv (ORCPT ); Fri, 29 Feb 2008 05:43:51 -0500 Subject: Re: Can Linux kernel handle unsynced TSC? From: Peter Zijlstra To: Zhao Forrest Cc: linux-kernel@vger.kernel.org, kvm-devel@lists.sourceforge.net In-Reply-To: References: Content-Type: text/plain Date: Fri, 29 Feb 2008 11:43:43 +0100 Message-Id: <1204281823.6243.78.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.21.90 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 735 Lines: 19 On Fri, 2008-02-29 at 16:55 +0800, Zhao Forrest wrote: > Sorry for reposting it. > > For example, > 1 rdtsc() is invoked on CPU0 > 2 process is migrated to CPU1, and rdtsc() is invoked on CPU1 > 3 if TSC on CPU1 is slower than TSC on CPU0, can kernel guarantee > that the second rdtsc() doesn't return a value smaller than the one > returned by the first rdtsc()? No, rdtsc() goes directly to the hardware. You need a (preferably cheap) clock abstraction layer on top if you need this. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/