Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S934016AbdC3OSX (ORCPT <rfc822;w@1wt.eu>);
        Thu, 30 Mar 2017 10:18:23 -0400
Received: from mail-wr0-f175.google.com ([209.85.128.175]:34937 "EHLO
        mail-wr0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S933426AbdC3OSV (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 30 Mar 2017 10:18:21 -0400
Date: Thu, 30 Mar 2017 16:18:17 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>, Rik van Riel <riel@redhat.com>,
        Luiz Capitulino <lcapitulino@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [BUG nohz]: wrong user and system time accounting
Message-ID: <20170330141816.GE3626@lerouge>
References: <20170323165512.60945ac6@redhat.com>
 <CANRm+CxcgSP2-x+A822DmHLvFLzFmTptS6oYwYtwVdErTpiB=Q@mail.gmail.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>
 <CANRm+CzfqkU6iV1BFk3PmWvy7MOsYH1mSwejJXMkvWW9C5ngwg@mail.gmail.com>
 <20170330133802.GC3626@lerouge>
 <CANRm+Cw8-7PydicanPCkNcVLi16Yr_0J9Sj6m6xWp4OUxLywjQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CANRm+Cw8-7PydicanPCkNcVLi16Yr_0J9Sj6m6xWp4OUxLywjQ@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 758
Lines: 14

On Thu, Mar 30, 2017 at 09:59:54PM +0800, Wanpeng Li wrote:
> 2017-03-30 21:38 GMT+08:00 Frederic Weisbecker <fweisbec@gmail.com>:
> > If it works, we may want to take that solution, likely less performance sensitive
> > than using sched_clock(). In fact sched_clock() is fast, especially as we require it to
> > be stable for nohz_full, but using it involves costly conversion back and forth to jiffies.
> 
> So both Rik and you agree with the skew tick solution, I will try it
> tomorrow. Btw, if we should just add random offset to the cpu in the
> nohz_full mode or add random offset to all cpus like the codes above?

Lets just keep it to all CPUs for simplicty.
Also please add a comment that explains why we need that skew_tick on nohz_full.

Thanks!