Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757237AbYJXARt (ORCPT ); Thu, 23 Oct 2008 20:17:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751813AbYJXARm (ORCPT ); Thu, 23 Oct 2008 20:17:42 -0400 Received: from one.firstfloor.org ([213.235.205.2]:41569 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751675AbYJXARl (ORCPT ); Thu, 23 Oct 2008 20:17:41 -0400 Date: Fri, 24 Oct 2008 02:25:11 +0200 From: Andi Kleen To: "H. Peter Anvin" Cc: akataria@vmware.com, Andi Kleen , Ingo Molnar , LKML , the arch/x86 maintainers , Daniel Hecht Subject: Re: [PATCH] Skip tsc synchronization checks if CONSTANT_TSC bit is set. Message-ID: <20081024002511.GC27492@one.firstfloor.org> References: <1224703427.13953.8.camel@alok-dev1> <20081022195845.GP12825@one.firstfloor.org> <1224712846.13953.37.camel@alok-dev1> <20081022221316.GW12825@one.firstfloor.org> <1224713518.13953.46.camel@alok-dev1> <20081022225409.GB27492@one.firstfloor.org> <1224728478.13953.79.camel@alok-dev1> <20081023081052.GI27492@one.firstfloor.org> <1224805162.21776.45.camel@alok-dev1> <49010D1E.8070400@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49010D1E.8070400@zytor.com> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 939 Lines: 19 > As far as skipping the check, it makes sense for me in the case of known > virtualization platforms; a CPU feature bit, real or synthetic, is a > very clean way to do that. I don't think adding detection for non PV Hypervisors is anywhere clean Even if it's only VMware today, tomorrow it will be a few more and long term you might need to support all of the obscuro hypervisors that are out there. Just seems like a slippery slope. Either it's paravirtual or it's not, but it should attempt to be both. If the hypervisor doesn't emulate TSC well enough that the native code works it's entirely reasonable to let it use some other timer, like it has been always done in the past. -Andi -- 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/