Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755340AbYJUSLl (ORCPT ); Tue, 21 Oct 2008 14:11:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755189AbYJUSLJ (ORCPT ); Tue, 21 Oct 2008 14:11:09 -0400 Received: from g1t0029.austin.hp.com ([15.216.28.36]:25864 "EHLO g1t0029.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755163AbYJUSLG (ORCPT ); Tue, 21 Oct 2008 14:11:06 -0400 From: Bjorn Helgaas To: "H. Peter Anvin" Subject: Re: [RFC patch 15/15] LTTng timestamp x86 Date: Tue, 21 Oct 2008 12:10:58 -0600 User-Agent: KMail/1.9.9 Cc: Linus Torvalds , john stultz , Mathieu Desnoyers , "Luck, Tony" , Steven Rostedt , Andrew Morton , Ingo Molnar , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , Peter Zijlstra , Thomas Gleixner , David Miller , Ingo Molnar References: <20081016232729.699004293@polymtl.ca> <48FD0633.70604@zytor.com> In-Reply-To: <48FD0633.70604@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200810211211.00332.bjorn.helgaas@hp.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1125 Lines: 25 On Monday 20 October 2008 04:29:07 pm H. Peter Anvin wrote: > Linus Torvalds wrote: > > > > But it's not going to solve the "hey, I have 512 CPU's, they are all on > > different boards, and no, they are _not_ synchronized to one global > > clock!". > > > > That's why I'd suggest making _purely_ local time, and then aiming for > > something NTP-like. But maybe there are better solutions out there. > > At the same time, it would definitely be nice to encourage vendors of > large SMP systems to provide a common root crystal (frequency standard) > for a single SMP domain. Preferrably a really good one, TCXO or better. A single root crystal is nice for us software guys. But it often also turns into a single point of failure, which the hardware guys are always trying to eliminate. So I think multiple crystals are inevitable for the really large machines. Bjorn -- 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/