Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933655AbdC3MwD (ORCPT ); Thu, 30 Mar 2017 08:52:03 -0400 Received: from mail-wr0-f193.google.com ([209.85.128.193]:35619 "EHLO mail-wr0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933173AbdC3MwB (ORCPT ); Thu, 30 Mar 2017 08:52:01 -0400 Date: Thu, 30 Mar 2017 14:51:58 +0200 From: Frederic Weisbecker To: Mike Galbraith Cc: Rik van Riel , Luiz Capitulino , Wanpeng Li , linux-kernel@vger.kernel.org Subject: Re: [BUG nohz]: wrong user and system time accounting Message-ID: <20170330125157.GB3626@lerouge> References: <20170323165512.60945ac6@redhat.com> <1490636129.8850.76.camel@redhat.com> <20170328132406.7d23579c@redhat.com> <20170329131656.1d6cb743@redhat.com> <1490818125.28917.11.camel@redhat.com> <1490848051.4167.57.camel@gmx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1490848051.4167.57.camel@gmx.de> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 847 Lines: 20 On Thu, Mar 30, 2017 at 06:27:31AM +0200, Mike Galbraith wrote: > On Wed, 2017-03-29 at 16:08 -0400, Rik van Riel wrote: > > > A random offset, or better yet a somewhat randomized > > tick length to make sure that simultaneous ticks are > > fairly rare and the vtime sampling does not end up > > "in phase" with the jiffies incrementing, could make > > the accounting work right again. > > That improves jitter, especially on big boxen. I have an 8 socket box > that thinks it's an extra large PC, there, collision avoidance matters > hugely. I couldn't reproduce bean counting woes, no idea if collision > avoidance will help that. Out of curiosity, where is the main contention between ticks? I indeed know some locks that can be taken on special cases, such as posix cpu timers. Also, why does it raise power consumption issues? Thanks.