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

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Message-ID: <alpine.DEB.2.20.1601200915170.21490@east.gentwo.org>
Date:	Wed, 20 Jan 2016 09:19:36 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	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, 20 Jan 2016, Thomas Gleixner wrote:

> > If the user makes use of full dynticks for soft isolation (for performance,
> > can live with a few interrupts...), there can be short moments of
> > multitasking.

"Soft" isolation? Like soft realtime ... Argh... Please stay away from
corrupting the intents of the nohz full mode.

> Again, you are trying to make the second step after the first one is
> completed. We do not even have proper accounting when we have the ONE task
> 100% case and still you try to solve problems beyond that.

Please lets only deal with the one task issue. I can have "soft" isolation
today by moving daemons etc off certain processors. We want definitely to
run nothing else on the processor and will want to even go further with
the cache allocation techniques in recent processor to limit the cache
disturbances from other processors etc etc.