linux-kernel - RE: [PATCH 10/14] scsi: only maintain target_blocked if the driver has a target queue limit

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Date:	Sat, 21 Jun 2014 22:10:14 +0000
From:	"Elliott, Robert (Server Storage)" <Elliott@...com>
To:	Christoph Hellwig <hch@....de>,
	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	Bart Van Assche <bvanassche@...ionio.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 10/14] scsi: only maintain target_blocked if the driver
 has a target queue limit



> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@....de]
> Sent: Thursday, 12 June, 2014 8:49 AM
> To: James Bottomley
> Cc: Jens Axboe; Bart Van Assche; Elliott, Robert (Server Storage); linux-
> scsi@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: [PATCH 10/14] scsi: only maintain target_blocked if the driver has a
> target queue limit
> 
> This saves us an atomic operation for each I/O submission and completion
> for the usual case where the driver doesn't set a per-target can_queue
> value.  Only a few iscsi hardware offload drivers set the per-target
> can_queue value at the moment.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/scsi/scsi_lib.c |   17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 0e33dee..763b3c9 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
...

> @@ -1642,7 +1648,8 @@ static void scsi_request_fn(struct request_queue *q)
>  	return;
> 
>   host_not_ready:
> -	atomic_dec(&scsi_target(sdev)->target_busy);
> +	if (&scsi_target(sdev)->can_queue > 0)
> +		atomic_dec(&scsi_target(sdev)->target_busy);
>   not_ready:
>  	/*
>  	 * lock q, handle tag, requeue req, and decrement device_busy. We

There's an extra & in that if statement.

---
Rob Elliott    HP Server Storage



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