linux-kernel - Re: [PATCH v6 3/4] block: implement runtime pm strategy

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Message-ID: <Pine.LNX.4.44L0.1301141306560.1782-100000@iolanthe.rowland.org>
Date:	Mon, 14 Jan 2013 13:13:32 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Aaron Lu <aaron.lu@...el.com>
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 v6 3/4] block: implement runtime pm strategy

On Mon, 14 Jan 2013, Aaron Lu wrote:

> On Tue, Jan 08, 2013 at 10:22:45AM -0500, Alan Stern wrote:
> > Just as importantly, all of the public routines added in patch 2/4 to
> > blk-core.c should have kerneldoc explaining how and where to use them.  
> > In particular, the kerneldoc for blk_pm_runtime_init() has to mention
> > that the block runtime PM implementation works only for drivers that
> > use request structures for their I/O; it doesn't work for drivers that
> > use bio's directly.
> 
> How about the following description for them?

Overall this is very good.

> /**
>  * blk_pm_runtime_init - Block layer runtime PM initialization routine
>  * @q: the queue of the device
>  * @dev: the device the queue belongs to
>  *
>  * Description:
>  *    Initialize runtime PM related fields for @q and start auto suspend
>  *    for @dev. Drivers that want to take advantage of request based runtime
>  *    PM should call this function after @dev has been initialized, and its
>  *    request queue @q has been allocated, and runtime PM for it is not
>  *    ready yet(either disabled/forbidden or its usage count >= 0).
>  *
>  *    The block layer runtime PM is request based, so only works for drivers
>  *    that use request as their IO unit instead of those directly use bio's.
>  */
> 
> /**
>  * blk_pre_runtime_suspend - Pre runtime suspend check
>  * @q: the queue of the device
>  *
>  * Description:
>  *    This function will check if runtime suspend is allowed for the device
>  *    by examining if there are any requests pending in the queue. If there
>  *    are requests pending, the device can not be runtime suspended; otherwise,
>  *    the queue's status will be updated to SUSPENDING and the driver can
>  *    proceed to suspend the device.
>  *
>  *    For the not allowed case, we mark last busy for the device so that
>  *    runtime PM core will try to autosuspend it some time later.
>  *
>  *    This function should be called in the device's runtime suspend callback,
>  *    before its runtime suspend function is called.

This doesn't quite make sense, because the runtime_suspend callback 
_is_ the runtime-suspend function.  How about "... should be called 
near the start of the device's runtime_suspend callback."?

A similar comment applies to the other functions.

>  *
>  * Return:
>  *    0		- OK to runtime suspend the device
>  *    -EBUSY	- Device should not be runtime suspended
>  */
> 
> /**
>  * blk_post_runtime_suspend - Post runtime suspend processing
>  * @q: the queue of the device
>  * @err: return value of the device's runtime suspend function
>  *
>  * Description:
>  *    Update the queue's runtime status according to the return value of the
>  *    device's runtime suspend function.
>  *
>  *    This function should be called in the device's runtime suspend callback,
>  *    after its runtime suspend function is called.
>  */
> 
> /**
>  * blk_pre_runtime_resume - Pre runtime resume processing
>  * @q: the queue of the device
>  *
>  * Description:
>  *    Update the queue's runtime status to RESUMING in preparation for the
>  *    runtime resume of the device.
>  *
>  *    This function should be called in the device's runtime resume callback,
>  *    before its runtime resume function is called.
>  */
> 
> /**
>  * blk_post_runtime_resume - Post runtime resume processing
>  * @q: the queue of the device
>  * @err: return value of the device's runtime resume function
>  *
>  * Description:
>  *    Update the queue's runtime status according to the return value of the
>  *    device's runtime resume function. If it is successfully resumed, process
>  *    the requests that are queued into the device's queue when it is resuming
>  *    and then mark last busy and initiate autosuspend for it.
>  *
>  *    This function should be called in the device's runtime resume callback,
>  *    after its runtime resume function is called.
>  */
> 
> Please feel free to suggest, thanks.

I would hypenate some of these words, such as "runtime-PM-related
fields" or "request-based runtime PM".  Also, "runtime_suspend" and 
"runtime_resume" generally should have either a '_' or a '-'.

But that's a very minor point; your descriptions are quite good.

Alan Stern

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