block: get rid of plug list sorting

Even if we have multiple queues in the plug list, chances that they
are very interspersed is minimal. Don't bother spending CPU cycles
sorting the list.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -19,7 +19,6 @@
 #include <linux/smp.h>
 #include <linux/interrupt.h>
 #include <linux/llist.h>
-#include <linux/list_sort.h>
 #include <linux/cpu.h>
 #include <linux/cache.h>
 #include <linux/sched/sysctl.h>
@@ -2161,20 +2160,6 @@ void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 	spin_unlock(&ctx->lock);
 }
 
-static int plug_rq_cmp(void *priv, const struct list_head *a,
-		       const struct list_head *b)
-{
-	struct request *rqa = container_of(a, struct request, queuelist);
-	struct request *rqb = container_of(b, struct request, queuelist);
-
-	if (rqa->mq_ctx != rqb->mq_ctx)
-		return rqa->mq_ctx > rqb->mq_ctx;
-	if (rqa->mq_hctx != rqb->mq_hctx)
-		return rqa->mq_hctx > rqb->mq_hctx;
-
-	return blk_rq_pos(rqa) > blk_rq_pos(rqb);
-}
-
 void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
 	LIST_HEAD(list);
@@ -2182,10 +2167,6 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 	if (list_empty(&plug->mq_list))
 		return;
 	list_splice_init(&plug->mq_list, &list);
-
-	if (plug->rq_count > 2 && plug->multiple_queues)
-		list_sort(NULL, &list, plug_rq_cmp);
-
 	plug->rq_count = 0;
 
 	do {