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Subject[PATCH] blk-mq: don't use rw_is_sync() to determine sync request
Date
Buffer read is counted as sync in rw_is_sync(). If we use it,
blk_sq_make_request() will not do per-process plug any more.

I haven't changed blk_mq_make_request() yet. It makes sense to dispatch
REQ_SYNC request immediately. But for buffer read, it's weird not to do
per-process plug, as buffer read doesn't need low latency.
blk_mq_merge_queue_io() isn't very helpful, as we don't have delay mechanism
there, the queue is immediately flushed, which makes the merge very
superficial.

Signed-off-by: Shaohua Li <shli@fb.com>
---
block/blk-mq.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index d5b4643..0ccbfac 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1106,7 +1106,7 @@ static struct request *blk_mq_map_request(struct request_queue *q,
ctx = blk_mq_get_ctx(q);
hctx = q->mq_ops->map_queue(q, ctx->cpu);

- if (rw_is_sync(bio->bi_rw))
+ if (bio->bi_rw & REQ_SYNC)
rw |= REQ_SYNC;

trace_block_getrq(q, bio, rw);
@@ -1206,7 +1206,7 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
*/
static void blk_sq_make_request(struct request_queue *q, struct bio *bio)
{
- const int is_sync = rw_is_sync(bio->bi_rw);
+ const int is_sync = !!(bio->bi_rw & REQ_SYNC);
const int is_flush_fua = bio->bi_rw & (REQ_FLUSH | REQ_FUA);
unsigned int use_plug, request_count = 0;
struct blk_map_ctx data;
--
1.8.3.2


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