linux-kernel - Re: [PATCH] bdi: use deferable timer for sync

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Date:	Fri, 08 Oct 2010 13:02:35 +0300
From:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
To:	ext Christoph Hellwig <hch@....de>
Cc:	Yong Wang <yong.y.wang@...ux.intel.com>,
	Jens Axboe <jaxboe@...ionio.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"xia.wu@...el.com" <xia.wu@...el.com>
Subject: Re: [PATCH] bdi: use deferable timer for sync_supers task

On Fri, 2010-10-08 at 11:25 +0200, ext Christoph Hellwig wrote:
> On Fri, Oct 08, 2010 at 04:35:14PM +0800, Yong Wang wrote:
> > sync_supers task currently wakes up periodically for superblock
> > writeback. This hurts power on battery driven devices. This patch
> > turns this housekeeping timer into a deferable timer so that it
> > does not fire when system is really idle.
> 
> How long can the timer be defereed?  We can't simply stop writing
> out data for a long time.  I think the current timer value should be
> the upper bound, but allowing to fire earlier to run during the
> same wakeup cycle as others is fine.

Infinitely.

There are range hrtimers which can do exactly what you said - you
specify the hard and soft limits there.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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