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List:       linux-scsi
Subject:    Re: [PATCH] scsi_debug: Simplify request tag decoding
From:       Douglas Gilbert <dgilbert () interlog ! com>
Date:       2018-01-31 13:41:30
Message-ID: 8e8335c3-d53a-475a-075d-9b852817a160 () interlog ! com
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On 2018-01-26 11:52 AM, Bart Van Assche wrote:
> Since commit 64d513ac31bd ("scsi: use host wide tags by default")
> all SCSI requests have a tag, whether or not scsi-mq is enabled.
> Additionally, it is safe to use blk_mq_unique_tag() and
> blk_mq_unique_tag_to_hwq() for legacy SCSI queues. Since this
> means that the sdebug_mq_active variable is superfluous, remove it.
> 
> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: Douglas Gilbert <dgilbert@interlog.com>

Ack-ed by Douglas Gilbert <dgilbert@interlog.com>

> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Hannes Reinecke <hare@suse.com>
> ---
>   drivers/scsi/scsi_debug.c | 37 +++++++++++--------------------------
>   1 file changed, 11 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index a5986dae9020..7d2ce0cc915a 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -649,7 +649,6 @@ static bool sdebug_any_injecting_opt;
>   static bool sdebug_verbose;
>   static bool have_dif_prot;
>   static bool sdebug_statistics = DEF_STATISTICS;
> -static bool sdebug_mq_active;
>   
>   static unsigned int sdebug_store_sectors;
>   static sector_t sdebug_capacity;	/* in sectors */
> @@ -3727,20 +3726,13 @@ static int resp_xdwriteread_10(struct scsi_cmnd *scp,
>   
>   static struct sdebug_queue *get_queue(struct scsi_cmnd *cmnd)
>   {
> -	struct sdebug_queue *sqp = sdebug_q_arr;
> +	u32 tag = blk_mq_unique_tag(cmnd->request);
> +	u16 hwq = blk_mq_unique_tag_to_hwq(tag);
>   
> -	if (sdebug_mq_active) {
> -		u32 tag = blk_mq_unique_tag(cmnd->request);
> -		u16 hwq = blk_mq_unique_tag_to_hwq(tag);
> -
> -		if (unlikely(hwq >= submit_queues)) {
> -			pr_warn("Unexpected hwq=%d, apply modulo\n", hwq);
> -			hwq %= submit_queues;
> -		}
> -		pr_debug("tag=%u, hwq=%d\n", tag, hwq);
> -		return sqp + hwq;
> -	} else
> -		return sqp;
> +	pr_debug("tag=%#x, hwq=%d\n", tag, hwq);
> +	if (WARN_ON_ONCE(hwq >= submit_queues))
> +		hwq = 0;
> +	return sdebug_q_arr + hwq;
>   }
>   
>   /* Queued (deferred) command completions converge here. */
> @@ -4587,9 +4579,8 @@ static int scsi_debug_show_info(struct seq_file *m, struct Scsi_Host *host)
>   		   num_host_resets);
>   	seq_printf(m, "dix_reads=%d, dix_writes=%d, dif_errors=%d\n",
>   		   dix_reads, dix_writes, dif_errors);
> -	seq_printf(m, "usec_in_jiffy=%lu, %s=%d, mq_active=%d\n",
> -		   TICK_NSEC / 1000, "statistics", sdebug_statistics,
> -		   sdebug_mq_active);
> +	seq_printf(m, "usec_in_jiffy=%lu, statistics=%d\n", TICK_NSEC / 1000,
> +		   sdebug_statistics);
>   	seq_printf(m, "cmnd_count=%d, completions=%d, %s=%d, a_tsf=%d\n",
>   		   atomic_read(&sdebug_cmnd_count),
>   		   atomic_read(&sdebug_completions),
> @@ -5612,13 +5603,8 @@ static int scsi_debug_queuecommand(struct Scsi_Host *shost,
>   				n += scnprintf(b + n, sb - n, "%02x ",
>   					       (u32)cmd[k]);
>   		}
> -		if (sdebug_mq_active)
> -			sdev_printk(KERN_INFO, sdp, "%s: tag=%u, cmd %s\n",
> -				    my_name, blk_mq_unique_tag(scp->request),
> -				    b);
> -		else
> -			sdev_printk(KERN_INFO, sdp, "%s: cmd %s\n", my_name,
> -				    b);
> +		sdev_printk(KERN_INFO, sdp, "%s: tag=%#x, cmd %s\n", my_name,
> +			    blk_mq_unique_tag(scp->request), b);
>   	}
>   	if (fake_host_busy(scp))
>   		return SCSI_MLQUEUE_HOST_BUSY;
> @@ -5782,8 +5768,7 @@ static int sdebug_driver_probe(struct device * dev)
>   	}
>   	/* Decide whether to tell scsi subsystem that we want mq */
>   	/* Following should give the same answer for each host */
> -	sdebug_mq_active = shost_use_blk_mq(hpnt) && (submit_queues > 1);
> -	if (sdebug_mq_active)
> +	if (shost_use_blk_mq(hpnt))
>   		hpnt->nr_hw_queues = submit_queues;
>   
>   	sdbg_host->shost = hpnt;
> 

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