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Subject[PATCH 6/8] block: enabling plugging on SSD devices that don't do queuing
Date
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>
---
block/blk-core.c | 13 +++++++++++--
1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index a32b571..c4198f0 100644
--- 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;
--
1.6.2.1.423.g442d


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