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Date: Wed, 20 Jan 2016 19:25:03 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Byungchul Park <byungchul.park@lge.com>,
        Chris Metcalf <cmetcalf@ezchip.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Luiz Capitulino <lcapitulino@redhat.com>,
        Christoph Lameter <cl@linux.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Mike Galbraith <efault@gmx.de>, Rik van Riel <riel@redhat.com>
Subject: Re: [RFC PATCH 4/4] sched: Upload nohz full CPU load on task
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On Wed, Jan 20, 2016 at 06:21:07PM +0100, Frederic Weisbecker wrote:

> You mean a periodic call to the above from the housekeepers?
> 
> I didn't think about doing that because you nacked that approach with
> scheduler_tick(). This isn't much different.

This does _one_ thing, namely load accounting. scheduler_tick() does a
whole bunch of things, some which really do not make much sense to do
remotely.

> It means the housekeeper is entirely dedicated to full dynticks CPUs.

Depends on how many there are, and how many housekeepers. I would
suggest one housekeeper cpu per node or so to make sure this keeps
working.

Then again, these load values aren't super important, esp. not for the
nohz_full case where you typically don't care about load balancing.