linux-kernel - Re: [PATCH v7 3/4] block: implement runtime pm strategy

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Date:	Sat, 19 Jan 2013 14:24:56 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Jens Axboe <axboe@...nel.dk>, "Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Aaron Lu <aaron.lwe@...il.com>,
	Shane Huang <shane.huang@....com>
Subject: Re: [PATCH v7 3/4] block: implement runtime pm strategy

On 01/18/2013 11:26 PM, Alan Stern wrote:
> On Fri, 18 Jan 2013, Aaron Lu wrote:
>
>>> Either you have to make sure the q->nr_pending is always correct, even
>>> when runtime PM isn't being used, or else the caller has to make sure
>>> that no I/O takes place before blk_pm_runtime_init is called.
>>
>> I think we can say:
>> blk_pm_runtime_init can't be called after any requests have been
>> submitted but not finished.
>> Sounds more accurate?
>
> Okay.  I think you can add (in parentheses) that in most cases drivers
> should call the routine before any I/O has taken place.

The reason I put it that way is, in patch 4, the blk_pm_runtime_init is
called after a request is executed(scsi_probe_lun). I do not want people
get confused by the comments for blk_pm_runtime_init and the example
code in patch 4 where we didn't follow it :-)

Considering ODD's use case, I was thinking of moving the
blk_pm_runtime_init call to sd.c, as sr will not use request based auto
suspend. Probably right before we decrease usage count for the device in
sd_probe_async. What do you think?

Thanks,
Aaron
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