From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
To: "ext Wu, Xia" <xia.wu@intel.com>
Cc: Christoph Hellwig <hch@lst.de>,
Yong Wang <yong.y.wang@linux.intel.com>,
Jens Axboe <jaxboe@fusionio.com>,
"Wu, Fengguang" <fengguang.wu@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: RE: [PATCH] bdi: use deferable timer for sync_supers task
Date: Fri, 08 Oct 2010 13:09:46 +0300 [thread overview]
Message-ID: <1286532586.2095.55.camel@localhost> (raw)
In-Reply-To: <A24AE1FFE7AEC5489F83450EE98351BF227AB58D43@shsmsx502.ccr.corp.intel.com>
On Fri, 2010-10-08 at 12:04 +0200, ext Wu, Xia 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.
>
> If the system is in sleep state, this timer can be deferred to the next wake-up interrupt.
> If the system is busy, this timer will fire at the scheduled time.
However, when the next wake-up interrupt happens is not defined. It can
happen 1ms after, or 1 minute after, or 1 hour after. What Christoph
says is that there should be some guarantee that sb writeout starts,
say, within 5 to 10 seconds interval. Deferrable timers do not guarantee
this. But take a look at the range hrtimers - they do exactly this.
--
Best Regards,
Artem Bityutskiy (D?N?N?N?D 1/4 D?D,N?N?N?DoD,D1)
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next prev parent reply other threads:[~2010-10-08 10:12 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-08 8:35 [PATCH] bdi: use deferable timer for sync_supers task Yong Wang
2010-10-08 9:25 ` Christoph Hellwig
2010-10-08 10:02 ` Artem Bityutskiy
2010-10-08 10:04 ` Wu, Xia
2010-10-08 10:09 ` Artem Bityutskiy [this message]
2010-10-08 10:27 ` Wu, Xia
2010-10-08 10:28 ` Artem Bityutskiy
2010-10-08 10:27 ` Yong Wang
2010-10-08 13:57 ` Wu Fengguang
2010-10-08 14:42 ` Wu Fengguang
2010-10-08 13:59 ` Artem Bityutskiy
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