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scsi: scsi_debug: Refine sdebug_blk_mq_poll()

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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.

Link: https://lore.kernel.org/r/20220109012853.301953-5-dgilbert@interlog.com
Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Douglas Gilbert 2022-01-08 20:28:48 -05:00 committed by Martin K. Petersen
parent 7d5a129b86
commit b05d4e481e
1 changed files with 16 additions and 5 deletions
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21
drivers/scsi/scsi_debug.c
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@ -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;