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SubjectRE: [PATCH 10/14] scsi: only maintain target_blocked if the driver has a target queue limit
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> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@lst.de]
> Sent: Thursday, 12 June, 2014 8:49 AM
> To: James Bottomley
> Cc: Jens Axboe; Bart Van Assche; Elliott, Robert (Server Storage); linux-
> scsi@vger.kernel.org; linux-kernel@vger.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@lst.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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