linux-kernel - Re: [RFC PATCH 3/3] block: add queue idle timer

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Date:	Thu, 17 May 2012 00:12:10 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jens Axboe <axboe@...nel.dk>, Jeff Moyer <jmoyer@...hat.com>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] block: add queue idle timer

On Wed, 2012-05-16 at 11:59 -0400, Alan Stern wrote:
> On Wed, 16 May 2012, Lin Ming wrote:
> 
> > > Lin, you should have more slack timer handling. Look at the blk-timeout
> > > handling of request timeouts for inspiration, and/or the thread that
> > > Jeff also references. Doing a timer add/del for each request put is a no
> > > go.
> > 
> > You mentioned how to detect queue idle in the referenced thread:
> > 	
> > ===
> > So we could probably add an idle timer that is set to some suitable
> > timeout for this and would be added when the queue first goes empty. If
> > new requests come in, just let it simmer and defer checking the state to
> > when it actually fires.
> 
> That is basically how the runtime PM timer works, if you use it as I 
> described earlier.
> 
> > ===
> > 
> > What do you mean of "the queue first goes empty"?
> 
> When the queue is first created, the timer is started.
> 
> Whenever the timer expires, the code checks to see if any requests have 
> been processed since the previous expiration.  If they have, the timer 
> is restarted.  If they haven't, you suspend the device.

And the timer is restarted when we resume the device, right?

> 
> Alan Stern
> 


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