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From: Douglas Gilbert <dgilbert@interlog.com>
To: linux-scsi@vger.kernel.org
Cc: martin.petersen@oracle.com, jejb@linux.vnet.ibm.com
Subject: [PATCH 4/9] scsi_debug: refine sdebug_blk_mq_poll
Date: Thu, 30 Dec 2021 21:08:24 -0500	[thread overview]
Message-ID: <20211231020829.29147-5-dgilbert@interlog.com> (raw)
In-Reply-To: <20211231020829.29147-1-dgilbert@interlog.com>

Refine the sdebug_blk_mq_poll() function so it only takes the
spinlock on the queue when it can see one or more requests
with the in_use bitmap flag set.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
 drivers/scsi/scsi_debug.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 6d50d248ff3a..0fe3fe0be8d6 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -7396,6 +7396,7 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 {
 	bool first;
 	bool retiring = false;
+	bool locked = false;
 	int num_entries = 0;
 	unsigned int qc_idx = 0;
 	unsigned long iflags;
@@ -7407,16 +7408,23 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 	struct sdebug_defer *sd_dp;
 
 	sqp = sdebug_q_arr + queue_num;
-	spin_lock_irqsave(&sqp->qc_lock, iflags);
+	qc_idx = find_first_bit(sqp->in_use_bm, sdebug_max_queue);
+	if (qc_idx >= sdebug_max_queue)
+		return 0;
 
 	for (first = true; first || qc_idx + 1 < sdebug_max_queue; )   {
+		if (!locked) {
+			spin_lock_irqsave(&sqp->qc_lock, iflags);
+			locked = true;
+		}
 		if (first) {
-			qc_idx = find_first_bit(sqp->in_use_bm, sdebug_max_queue);
 			first = false;
+			if (!test_bit(qc_idx, sqp->in_use_bm))
+				continue;
 		} else {
 			qc_idx = find_next_bit(sqp->in_use_bm, sdebug_max_queue, qc_idx + 1);
 		}
-		if (unlikely(qc_idx >= sdebug_max_queue))
+		if (qc_idx >= sdebug_max_queue)
 			break;
 
 		sqcp = &sqp->qc_arr[qc_idx];
@@ -7465,11 +7473,14 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 		}
 		WRITE_ONCE(sd_dp->defer_t, SDEB_DEFER_NONE);
 		spin_unlock_irqrestore(&sqp->qc_lock, iflags);
+		locked = false;
 		scsi_done(scp); /* callback to mid level */
-		spin_lock_irqsave(&sqp->qc_lock, iflags);
 		num_entries++;
+		if (find_first_bit(sqp->in_use_bm, sdebug_max_queue) >= sdebug_max_queue)
+			break;	/* if no more then exit without retaking spinlock */
 	}
-	spin_unlock_irqrestore(&sqp->qc_lock, iflags);
+	if (locked)
+		spin_unlock_irqrestore(&sqp->qc_lock, iflags);
 	if (num_entries > 0)
 		atomic_add(num_entries, &sdeb_mq_poll_count);
 	return num_entries;
-- 
2.25.1


  parent reply	other threads:[~2021-12-31  2:16 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-31  2:08 [PATCH 0/9] scsi_debug: collection of additions Douglas Gilbert
2021-12-31  2:08 ` [PATCH 1/9] scsi_debug: address races following module load Douglas Gilbert
2022-01-05 19:41   ` Bart Van Assche
2022-01-12  3:39   ` Luis Chamberlain
2021-12-31  2:08 ` [PATCH 2/9] scsi_debug: strengthen defer_t accesses Douglas Gilbert
2021-12-31  2:08 ` [PATCH 3/9] scsi_debug: use task set full more Douglas Gilbert
2021-12-31  2:08 ` Douglas Gilbert [this message]
2021-12-31  2:08 ` [PATCH 5/9] scsi_debug: divide power on reset unit attention Douglas Gilbert
2021-12-31  2:08 ` [PATCH 6/9] scsi_debug: add no_rwlock parameter Douglas Gilbert
2021-12-31  2:08 ` [PATCH 7/9] scsi_debug: add sdeb_sgl_copy_sgl and friends Douglas Gilbert
2021-12-31  2:08 ` [PATCH 8/9] scsi_debug: change store from vmalloc to sgl Douglas Gilbert
2022-01-05  9:28   ` Shinichiro Kawasaki
2021-12-31  2:08 ` [PATCH 9/9] scsi_debug: add environmental reporting log subpage Douglas Gilbert
2021-12-31 22:43 [PATCH 8/9] scsi_debug: change store from vmalloc to sgl kernel test robot
2022-01-07  6:57 ` Dan Carpenter

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