block: make rq sector size accessible for block stats

Currently rq->data_len will be decreased by partial completion or
zeroed by completion, so when blk_stat_add() is invoked, data_len
will be zero and there will never be samples in poll_cb because
blk_mq_poll_stats_bkt() will return -1 if data_len is zero.

We could move blk_stat_add() back to __blk_mq_complete_request(),
but that would make the effort of trying to call ktime_get_ns()
once in vain. Instead we can reuse throtl_size field, and use
it for both block stats and block throttle, and adjust the
logic in blk_mq_poll_stats_bkt() accordingly.

Fixes: 4bc6339a583c ("block: move blk_stat_add() to __blk_mq_end_request()")
Tested-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3647776a0f6eefeaef8d9d0afe6ea9ef3eebbe11..d30fabb583fd568f29056b0b2330a49ee80a1452 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -44,12 +44,12 @@ static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb);
 
 static int blk_mq_poll_stats_bkt(const struct request *rq)
 {
-       int ddir, bytes, bucket;
+       int ddir, sectors, bucket;
 
        ddir = rq_data_dir(rq);
-       bytes = blk_rq_bytes(rq);
+       sectors = blk_rq_stats_sectors(rq);
 
-       bucket = ddir + 2*(ilog2(bytes) - 9);
+       bucket = ddir + 2 * ilog2(sectors);
 
        if (bucket < 0)
                return -1;
@@ -333,6 +333,7 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
        else
                rq->start_time_ns = 0;
        rq->io_start_time_ns = 0;
+       rq->stats_sectors = 0;
        rq->nr_phys_segments = 0;
 #if defined(CONFIG_BLK_DEV_INTEGRITY)
        rq->nr_integrity_segments = 0;
@@ -681,9 +682,7 @@ void blk_mq_start_request(struct request *rq)
 
        if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
                rq->io_start_time_ns = ktime_get_ns();
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-               rq->throtl_size = blk_rq_sectors(rq);
-#endif
+               rq->stats_sectors = blk_rq_sectors(rq);
                rq->rq_flags |= RQF_STATS;
                rq_qos_issue(q, rq);
        }

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 0445c998c3772f00a4e63cda63bf6765526abe4f..18f773e52dfb1d8da00b3809171e106cca780f87 100644 (file)
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -2248,7 +2248,8 @@ void blk_throtl_stat_add(struct request *rq, u64 time_ns)
        struct request_queue *q = rq->q;
        struct throtl_data *td = q->td;
 
-       throtl_track_latency(td, rq->throtl_size, req_op(rq), time_ns >> 10);
+       throtl_track_latency(td, blk_rq_stats_sectors(rq), req_op(rq),
+                            time_ns >> 10);
 }
 
 void blk_throtl_bio_endio(struct bio *bio)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index b196124e324083c982c2bcfb1ffd4f406e6867d6..3094f2d513b2368d1ba5d2df9cf9f92de1c84954 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -206,9 +206,12 @@ struct request {
 #ifdef CONFIG_BLK_WBT
        unsigned short wbt_flags;
 #endif
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-       unsigned short throtl_size;
-#endif
+       /*
+        * rq sectors used for blk stats. It has the same value
+        * with blk_rq_sectors(rq), except that it never be zeroed
+        * by completion.
+        */
+       unsigned short stats_sectors;
 
        /*
         * Number of scatter-gather DMA addr+len pairs after
@@ -917,6 +920,7 @@ static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
  * blk_rq_err_bytes()          : bytes left till the next error boundary
  * blk_rq_sectors()            : sectors left in the entire request
  * blk_rq_cur_sectors()                : sectors left in the current segment
+ * blk_rq_stats_sectors()      : sectors of the entire request used for stats
  */
 static inline sector_t blk_rq_pos(const struct request *rq)
 {
@@ -945,6 +949,11 @@ static inline unsigned int blk_rq_cur_sectors(const struct request *rq)
        return blk_rq_cur_bytes(rq) >> SECTOR_SHIFT;
 }
 
+static inline unsigned int blk_rq_stats_sectors(const struct request *rq)
+{
+       return rq->stats_sectors;
+}
+
 #ifdef CONFIG_BLK_DEV_ZONED
 static inline unsigned int blk_rq_zone_no(struct request *rq)
 {