linux-kernel - Re: [RFC PATCH 4/4] sched: Upload nohz full CPU load on task enqueue/dequeue

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Message-ID: <20160120164726.GD24537@lerouge>
Date:	Wed, 20 Jan 2016 17:47:27 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Byungchul Park <byungchul.park@....com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>
Subject: Re: [RFC PATCH 4/4] sched: Upload nohz full CPU load on task
 enqueue/dequeue

On Wed, Jan 20, 2016 at 10:42:56AM -0600, Christoph Lameter wrote:
> On Wed, 20 Jan 2016, Frederic Weisbecker wrote:
> 
> > > So we agreed long time ago, that we first fix the issues with s single task
> > > running undisturbed in user space, i.e. tickless. Those issues have never been
> > > resolved fully, but now you try to add more complexity of extra runnable
> > > tasks, nohz tasks sleeping and whatever.
> >
> > Nohz tasks do sleep, really, at least we need to handle that case now.
> 
> Sleep meaning call into the OS to be put to sleep?

Indeed, when the task has finished its work, it goes to sleep, right?

> Why would NOHZ be active then?

It's active when the task active.