Message-ID: <1502810123.1349.71.camel@gmx.de>
Subject: Re: [RFC PATCH 7/9] housekeeping: Use own boot option, independant
 from nohz
From: Mike Galbraith <efault@gmx.de>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Chris Metcalf <cmetcalf@mellanox.com>,
        Thomas Gleixner <tglx@linutronix.de>, Christoph Lameter <cl@linux.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@redhat.com>,
        Wanpeng Li <kernellwp@gmail.com>
Date: Tue, 15 Aug 2017 17:15:23 +0200
In-Reply-To: <20170815130712.GA16627@lerouge>
References: <1500643290-25842-1-git-send-email-fweisbec@gmail.com>
         <1500643290-25842-8-git-send-email-fweisbec@gmail.com>
         <20170811123927.33e094f3@redhat.com> <20170812141004.GA21918@lerouge>
         <20170813111340.0ade6d58@redhat.com> <20170814170107.GA27479@lerouge>
         <20170814133440.3dc31bad@redhat.com> <1502735386.31351.61.camel@gmx.de>
         <20170815130712.GA16627@lerouge>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1145
Lines: 23

On Tue, 2017-08-15 at 15:07 +0200, Frederic Weisbecker wrote:
> On Mon, Aug 14, 2017 at 08:29:46PM +0200, Mike Galbraith wrote:
> > On Mon, 2017-08-14 at 13:34 -0400, Luiz Capitulino wrote:
> > > On Mon, 14 Aug 2017 19:01:09 +0200
> > > 
> > > > What is the source of the load balancing inducing such latency when a single
> > > > task is affine to a CPU? If this is idle load balancing, it is now affine to
> > > > housekeepers. If this is task wakeup then it's suprising because select_task_rq()
> > > > is optimized toward single CPU affinity.
> > > 
> > > I guess it was idle load balancing, but I don't remember because this
> > > was a few years ago. I think this might be reproducible without using
> > > isolcpus=. I'll give it a try shortly and let you know.
> > 
> > idle_balance() can swamp other noise by a couple orders of magnitude,
> 
> Ah I missed that one. Is there any way we can also lower the overhead there?

Why?  HPC proggies won't benefit from a partially filled pothole any
more that a ~zero ground clearance formula 1 car would.  The pothole
intolerant either isolate, killing (most) LB, or they meet a wall.

	-Mike