Date: Fri, 1 Sep 2017 01:00:00 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Chris Metcalf <cmetcalf@mellanox.com>,
        Luiz Capitulino <lcapitulino@redhat.com>,
        Christoph Lameter <cl@linux.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, Mike Galbraith <efault@gmx.de>,
        Rik van Riel <riel@redhat.com>, Wanpeng Li <kernellwp@gmail.com>
Subject: Re: [RFC PATCH 12/12] housekeeping: Reimplement isolcpus on
 housekeeping
Message-ID: <20170831225959.GB18249@lerouge>
References: <1503453071-952-1-git-send-email-fweisbec@gmail.com>
 <1503453071-952-13-git-send-email-fweisbec@gmail.com>
 <20170828100957.jcjhh77ylxvsyisy@hirez.programming.kicks-ass.net>
 <20170828132302.GA32618@lerouge>
 <20170828133116.zu3xujkkmb4cmks2@hirez.programming.kicks-ass.net>
 <20170828152714.GB32618@lerouge>
 <20170828162416.nmdfvutqaki4sahx@hirez.programming.kicks-ass.net>
 <20170828173315.GA3631@lerouge>
 <alpine.DEB.2.20.1708312050040.2346@nanos>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <alpine.DEB.2.20.1708312050040.2346@nanos>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1180
Lines: 22

On Thu, Aug 31, 2017 at 08:53:56PM +0200, Thomas Gleixner wrote:
> On Mon, 28 Aug 2017, Frederic Weisbecker wrote:
> > On Mon, Aug 28, 2017 at 06:24:16PM +0200, Peter Zijlstra wrote:
> > > On Mon, Aug 28, 2017 at 05:27:15PM +0200, Frederic Weisbecker wrote:
> > > > Although for example I guess (IIUC) that if you create an unbound
> > > > timer on a NULL domain, it will be stuck on it for ever as we can't
> > > > walk any hierarchy from the current CPU domain.
> > > 
> > > Not sure what you're on about. Timers have their own hierarchy.
> > 
> > Check out get_nohz_timer_target() which relies on scheduler hierarchies to
> > look up a CPU to enqueue an unpinned timer on.
> 
> Which is one of the most idiotic things we have in that code
> path. Anna-Maria has posted this series which gets rid of that nonsense, by
> queueing the timer on the current cpu into a wheel, which gets pulled in by
> others. That makes a lot of sense because most of these timers get canceled
> before expiry anyway. But we still need to fix the fallout and the few
> corner cases to make that work reliably. We'll do that hopefully sooner
> than later.

Sure, I definetly agree with that change.