linux-kernel - Re: [BUG nohz]: wrong user and system time accounting

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Message-ID: <20170330141816.GE3626@lerouge>
Date:   Thu, 30 Mar 2017 16:18:17 +0200
From:   Frederic Weisbecker <fweisbec@...il.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [BUG nohz]: wrong user and system time accounting

On Thu, Mar 30, 2017 at 09:59:54PM +0800, Wanpeng Li wrote:
> 2017-03-30 21:38 GMT+08:00 Frederic Weisbecker <fweisbec@...il.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!