Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754930AbdC3WWW (ORCPT ); Thu, 30 Mar 2017 18:22:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45184 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752744AbdC3WWU (ORCPT ); Thu, 30 Mar 2017 18:22:20 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 19C057F3EC Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=dhowells@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 19C057F3EC Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <22214.1490895007@warthog.procyon.org.uk> <23410.1490902528@warthog.procyon.org.uk> <23902.1490904827@warthog.procyon.org.uk> To: Linus Torvalds Cc: dhowells@redhat.com, Thomas Gleixner , John Stultz , Linux Kernel Mailing List , linux-fsdevel Subject: Re: Apparent backward time travel in timestamps on file creation MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <26742.1490912537.1@warthog.procyon.org.uk> Date: Thu, 30 Mar 2017 23:22:17 +0100 Message-ID: <26743.1490912537@warthog.procyon.org.uk> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 30 Mar 2017 22:22:19 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 886 Lines: 21 Linus Torvalds wrote: > The "is it in sync with gettimeofday()" is interesting too, even if > the answer is that you don't expect it to be _perfectly_ in sync. A > test that just reports maximum slop might be an interesting test, and > could show real problems (maybe bad network time synchronization, but > maybe actual bugs in our internal xtime handling even for local > filesystems!). I wonder if multi-cpu systems might show interesting differences between CPUs too. I would hope not since xtime is based on a global variable. > And then if your tool starts reporting times that are off by seconds > or minutes, people might say "Hey, that's not right.." and find > something. More likely never see it as the output is hidden away by xfstests. Probably xfstests needs to gain some way of lending prominence to information of this type. David