linux-kernel - RE: unnecessary timer interrupt of slab.c and bdi tasks when the system is in sleep state

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Date:	Fri, 1 Oct 2010 07:22:10 -0700
From:	"Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
CC:	"Wu, Xia" <xia.wu@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Zhu, Daniel" <daniel.zhu@...el.com>,
	"Wang, Yong Y" <yong.y.wang@...el.com>
Subject: RE: unnecessary timer interrupt of slab.c and bdi tasks when the
	system is in sleep state

> > > I found some unnecessary timer interrupts when the system enter
> sleep state.
> > > (1)     /mm/slab.c
> > > cache_reap() clean up on allocated memory every 2s. If the system
> is in sleep state, the system is waked-up when this timer expires. In
> fact,
> > > there isn't more slabs to been cleaned up in sleep state.
> >
> > Right. We could switch off the timer when idle without much of an
> issue.
> > The expiration of the caches wont occur and so we will have stale
> objects
> > on the queues when we exit sleep state. You could flush the queues
> before
> > switching off the timers?
> 
> 
> May be flushing the queue everytime we enter nohz is too much, as that
> can
> happen very often?
> 


the slab timer is already deferable... which means it won't hit while the system is completely idle.
I think this part of the original report is a red herring found on an older kernel.

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