From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF994C43382 for ; Thu, 27 Sep 2018 14:41:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A330121547 for ; Thu, 27 Sep 2018 14:41:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A330121547 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728062AbeI0U7w (ORCPT ); Thu, 27 Sep 2018 16:59:52 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:52146 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727076AbeI0U7w (ORCPT ); Thu, 27 Sep 2018 16:59:52 -0400 Received: from p5492e4c1.dip0.t-ipconnect.de ([84.146.228.193] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1g5XTd-0005NL-EC; Thu, 27 Sep 2018 16:41:13 +0200 Date: Thu, 27 Sep 2018 16:41:12 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: John Stultz , Andy Lutomirski , LKML , X86 ML , Matt Rickard , Stephen Boyd , Florian Weimer , "K. Y. Srinivasan" , Vitaly Kuznetsov , devel@linuxdriverproject.org, Linux Virtualization , Paolo Bonzini , Arnd Bergmann , Juergen Gross Subject: Re: [patch 09/11] x86/vdso: Simplify the invalid vclock case In-Reply-To: Message-ID: References: <20180914125006.349747096@linutronix.de> <20180914125118.909646643@linutronix.de> <20180918083055.GJ24106@hirez.programming.kicks-ass.net> <20180918124800.GL24106@hirez.programming.kicks-ass.net> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 Sep 2018, Thomas Gleixner wrote: > On Tue, 18 Sep 2018, Thomas Gleixner wrote: > > So if the TSC on CPU1 is slightly behind the TSC on CPU0 then now1 can be > > smaller than cycle_last. The TSC sync stuff does not catch the small delta > > for unknown raisins. I'll go and find that machine and test that again. > > Of course it does not trigger anymore. We accumulated code between the > point in timekeeping_advance() where the TSC is read and the update of the > VDSO data. > > I'll might have to get an 2.6ish kernel booted on that machine and try with > that again. /me shudders Actually it does happen, because the TSC is very slowly drifting apart due to SMI wreckage trying to hide itself. It just takes a very long time. Thanks, tglx