linux-kernel - Re: [PATCH v4 3/4] block: implement runtime pm strategy

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Date:	Thu, 5 Jul 2012 09:54:09 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lin Ming <ming.m.lin@...el.com>
cc:	Jens Axboe <axboe@...nel.dk>, Shaohua Li <shli@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<linux-scsi@...r.kernel.org>
Subject: Re: [PATCH v4 3/4] block: implement runtime pm strategy

On Thu, 5 Jul 2012, 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.
> 
> Signed-off-by: Lin Ming <ming.m.lin@...el.com>

These changes would look better if you didn't have "#ifdef
CONFIG_PM_RUNTIME" sprinkled throughout the block-layer routines.

Instead, define static helper functions to do your work, and put the 
definitions inside a #ifdef block.  If CONFIG_PM_RUNTIME isn't enabled,
the helper functions can be empty static inlines.
 
> --- a/block/elevator.c +++ b/block/elevator.c @@ -536,6 +537,11 @@

> void elv_requeue_request(struct request_queue *q, struct request *rq)
>  
>  	rq->cmd_flags &= ~REQ_STARTED;
>  
> +#ifdef CONFIG_PM_RUNTIME
> +	/* __elv_add_request will increment the count */
> +	if (!(rq->cmd_flags & REQ_PM))
> +		q->nr_pending--;
> +#endif

__elv_add_request increments nr_pending even when REQ_PM is set.  You 
need to be consistent with that behavior.

Alan Stern

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