block: enabling plugging on SSD devices that don't do queuing

For the older SSD devices that don't do command queuing, we do want to
enable plugging to get better merging.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/block/blk-core.c b/block/blk-core.c
index a32b571..c4198f0 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1136,6 +1136,15 @@ void init_request_from_bio(struct request *req, struct bio *bio)
        blk_rq_bio_prep(req->q, req, bio);
 }
 
+/*
+ * Only disabling plugging for non-rotational devices if it does tagging
+ * as well, otherwise we do need the proper merging
+ */
+static inline bool queue_should_plug(struct request_queue *q)
+{
+       return !(blk_queue_nonrot(q) && blk_queue_tagged(q));
+}
+
 static int __make_request(struct request_queue *q, struct bio *bio)
 {
        struct request *req;
@@ -1242,11 +1251,11 @@ get_rq:
        if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) ||
            bio_flagged(bio, BIO_CPU_AFFINE))
                req->cpu = blk_cpu_to_group(smp_processor_id());
-       if (!blk_queue_nonrot(q) && elv_queue_empty(q))
+       if (queue_should_plug(q) && elv_queue_empty(q))
                blk_plug_device(q);
        add_request(q, req);
 out:
-       if (unplug || blk_queue_nonrot(q))
+       if (unplug || !queue_should_plug(q))
                __generic_unplug_device(q);
        spin_unlock_irq(q->queue_lock);
        return 0;