Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758706AbZCOUgM (ORCPT ); Sun, 15 Mar 2009 16:36:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754162AbZCOUf4 (ORCPT ); Sun, 15 Mar 2009 16:35:56 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:60824 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751375AbZCOUfz (ORCPT ); Sun, 15 Mar 2009 16:35:55 -0400 Date: Sun, 15 Mar 2009 13:32:42 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Jesper Krogh cc: john stultz , Thomas Gleixner , Linux Kernel Mailing List , Len Brown Subject: Re: Linux 2.6.29-rc6 In-Reply-To: <49BD4B2D.7000501@krogh.cc> Message-ID: References: <49A6FEE2.90700@krogh.cc> <1f1b08da0902261319k7a60d80xaafc1101facfd2d9@mail.gmail.com> <49A70B24.6090706@krogh.cc> <1235685269.6811.11.camel@localhost.localdomain> <1235687483.6811.26.camel@localhost.localdomain> <49A78C79.304@krogh.cc> <1235766936.7402.5.camel@localhost.localdomain> <49AD90E2.7050209@krogh.cc> <1236118969.6068.87.camel@localhost> <49AE9EA4.2080500@krogh.cc> <49AECA3B.5030503@krogh.cc> <1236193075.3793.63.camel@jstultz-laptop> <1236220759.6863.7.camel@localhost.localdomain> <1236221530.6863.9.camel@localhost.localdomain> <49B57F3D.5030008@krogh.cc> <49BD225C.4070305@krogh.cc> <49BD4B2D.7000501@krogh.cc> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1702 Lines: 38 On Sun, 15 Mar 2009, Jesper Krogh wrote: > > I went on to trying Thomas Gleixners patch (which seems to do excactly the > same .. ), I'll write a reply in to that message in a few minutes. Side note: no, Thomas' patch doesn't do at all exactly the same. It does something similar, in that it looks at the time differences between calls to the whole "wait for the PIT MSB to change" function, but those differences _could_ in theory be very small, even if the error is very big. That's especially true if the PIT read ends up serializing with the PIT, so that the "wait for MSB" essentially always takes exactly the same amount of cycles (giving a zero error estimation in Thomas' version), but the reads themselves can still be quite slow (giving a non-zero error term in the end result). IOW, Thomas' patch is good at finding variability in the reads - which could be the result of SMM interaction, while my patch literally measures how long it takes to read the MSB change. Now in practice I suspect the variability in the MSB reads _probably_ correlate reasonably well with how long a single PIT read will take (ie rather than finding variability due to SMM interaction, it will find variability due to the "quanitization" effect of the reads taking a reasonably long time), so I suspect that in many cases Thomas' patch will error out for the same cases mine does. But the two patches are rather fundamentally different. Linus -- 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/