blk-mq: account higher order dispatch

We currently account a '0' dispatch, and anything above that still falls
below the range set by BLK_MQ_MAX_DISPATCH_ORDER. If we dispatch more,
we don't account it.

Change the last bucket to be inclusive of anything above the range we
track, and have the sysfs file reflect that by including a '+' in the
output:

$ cat /sys/block/nvme0n1/mq/0/dispatched
        0	1006
        1	20229
        2	1
        4	0
        8	0
       16	0
       32+	0
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>

block/blk-mq-sysfs.c

@@ -208,12 +208,14 @@ static ssize_t blk_mq_hw_sysfs_dispatched_show(struct blk_mq_hw_ctx *hctx,
 
 	page += sprintf(page, "%8u\t%lu\n", 0U, hctx->dispatched[0]);
 
-	for (i = 1; i < BLK_MQ_MAX_DISPATCH_ORDER; i++) {
-		unsigned long d = 1U << (i - 1);
+	for (i = 1; i < BLK_MQ_MAX_DISPATCH_ORDER - 1; i++) {
+		unsigned int d = 1U << (i - 1);
 
-		page += sprintf(page, "%8lu\t%lu\n", d, hctx->dispatched[i]);
+		page += sprintf(page, "%8u\t%lu\n", d, hctx->dispatched[i]);
 	}
 
+	page += sprintf(page, "%8u+\t%lu\n", 1U << (i - 1),
+						hctx->dispatched[i]);
 	return page - start_page;
 }
 

block/blk-mq.c

@@ -789,6 +789,14 @@ static void flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list)
 	}
 }
 
+static inline unsigned int queued_to_index(unsigned int queued)
+{
+	if (!queued)
+		return 0;
+
+	return min(BLK_MQ_MAX_DISPATCH_ORDER - 1, ilog2(queued) + 1);
+}
+
 /*
  * Run this hardware queue, pulling any software queues mapped to it in.
  * Note that this function currently has various problems around ordering
@@ -877,10 +885,7 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 			dptr = &driver_list;
 	}
 
-	if (!queued)
-		hctx->dispatched[0]++;
-	else if (queued < (1 << (BLK_MQ_MAX_DISPATCH_ORDER - 1)))
-		hctx->dispatched[ilog2(queued) + 1]++;
+	hctx->dispatched[queued_to_index(queued)]++;
 
 	/*
 	 * Any items that need requeuing? Stuff them into hctx->dispatch,