linux-kernel - Re: [PATCH v5 3/4] block: implement runtime pm strategy

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Message-ID: <20120706072752.GD17681@parisc-linux.org>
Date:	Fri, 6 Jul 2012 01:27:52 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Alan Stern <stern@...land.harvard.edu>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Shaohua Li <shli@...nel.org>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH v5 3/4] block: implement runtime pm strategy

On Fri, Jul 06, 2012 at 12:04:31PM +0800, Lin Ming wrote:
> When a request is added:
>     If device is suspended or is suspending and the request is not a
>     PM request, resume the device.
> 
> When a request finishes:
>     Call pm_runtime_mark_last_busy().
> 
> When pick a request:
>     If device is resuming/suspending, then only PM request is allowed to go.
>     Return NULL for other cases.

This only works for drivers which are struct request based.  For those
that handle struct bio directly, nr_pending will always be 0.

I think the right place to increment nr_pending is in generic_make_request.
But I'm not sure where to decrement it.  I think we need a blk_bio_endio()
which does some housekeeping and then calls bio_endio().

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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