Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S965391AbdLVJMn (ORCPT <rfc822;w@1wt.eu>);
        Fri, 22 Dec 2017 04:12:43 -0500
Received: from merlin.infradead.org ([205.233.59.134]:39234 "EHLO
        merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S932637AbdLVJM2 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 22 Dec 2017 04:12:28 -0500
Date: Fri, 22 Dec 2017 10:12:21 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Brendan Jackman <brendan.jackman@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>
Subject: Re: [RFC PATCH 2/5] sched: Add NOHZ_STATS_KICK
Message-ID: <20171222091221.ow5vn3ydx3hj4nht@hirez.programming.kicks-ass.net>
References: <20171221102139.177253391@infradead.org>
 <20171221102235.088181011@infradead.org>
 <CAKfTPtCi_0JAvBmY4QGVAGaB_wMJJEDZ1dob8gAsHR21TuhJCg@mail.gmail.com>
 <CAKfTPtCVgnO1zcD_X4Ad-T0auWmN-TJ0dezv0P5wEtubkbgHyQ@mail.gmail.com>
 <20171222075934.f6yenvcb2zkf2ysd@hirez.programming.kicks-ass.net>
 <CAKfTPtC0+5zjvgNXMyVcvnnyJh0giQgJHtx+5p-GEpjUW1x8eg@mail.gmail.com>
 <20171222082915.4lcb7xyyooqyjpia@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171222082915.4lcb7xyyooqyjpia@hirez.programming.kicks-ass.net>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 934
Lines: 21

On Fri, Dec 22, 2017 at 09:29:15AM +0100, Peter Zijlstra wrote:
> On Fri, Dec 22, 2017 at 09:05:45AM +0100, Vincent Guittot wrote:
> > On 22 December 2017 at 08:59, Peter Zijlstra <peterz@infradead.org> wrote:
> > > On Thu, Dec 21, 2017 at 05:56:32PM +0100, Vincent Guittot wrote:
> > >> In fact, we can't only rely on the tick and newly_idle load balance to
> > >> ensure a period update of the blocked load because they can never
> > >> happen.
> > >
> > > I'm confused, why would the ilb not happen?
> > 
> > the ilb will be kick only if tick fires which might not be the case
> > for task that runs less than a tick
> 
> Oh, urgh, you're talking about when the entire system is idle. Yes
> indeed.
> 
> Lemme have a think, surely we can do something saner there.

The only thing I could come up with is running a timer for this :/ That
would keep the ILB thing running until all load is decayed (have a patch
for that somewhere).