linux-kernel - Re: RFC: THE OFFLINE SCHEDULER

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Date:	Mon, 31 Aug 2009 15:19:15 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Gregory Haskins <ghaskins@...ell.com>,
	Rik van Riel <riel@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>,
	raz ben yehuda <raziebe@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu,
	peterz@...radead.org, maximlevitsky@...il.com, efault@....de,
	wiseman@...s.biu.ac.il, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: RFC: THE OFFLINE SCHEDULER

On Fri, 28 Aug 2009, Thomas Gleixner wrote:

> > slab does run a timer every 2 second to age queues. If there was activity
> > then there can be a relatively long time in which we periodically throw
> > out portions of the cached data.
>
> Right, but why does that affect a CPU which is marked "I'm not
> involved in that game" ?

Its run unconditionally on every processor. System needs to scan through
all slabs and all queues to figure out if there is something to expire.

> > The device may periodically check for conditions that require action.
>
> Errm. The device is associated to some other CPU, so why would it
> require action on an isolated one ? Or are you talking about a device
> which is associated to that isolated CPU ?

Some devices now have per cpu threads. See f.e. Mellanox IB drivers. Maybe
there is a way to restrict that.


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