[PATCH] device-mapper disk statistics: timing

Record I/O timing statistics

The start time is added to struct dm_io, an existing structure allocated
privately internally within dm and attached to each incoming bio.

We export disk_round_stats() from block/ll_rw_blk.c instead of creating a
private clone.

Signed-off-by: Jun'ichi "Nick" Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 33 insertions, 2 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index c47518386c9..e9adeb9d172 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -31,6 +31,7 @@ struct dm_io {
         int error;
         struct bio *bio;
         atomic_t io_count;
+        unsigned long start_time;
 };
 
 /*
@@ -244,6 +245,36 @@ static inline void free_tio(struct mapped_device *md, struct target_io *tio)
         mempool_free(tio, md->tio_pool);
 }
 
+static void start_io_acct(struct dm_io *io)
+{
+        struct mapped_device *md = io->md;
+
+        io->start_time = jiffies;
+
+        preempt_disable();
+        disk_round_stats(dm_disk(md));
+        preempt_enable();
+        dm_disk(md)->in_flight = atomic_inc_return(&md->pending);
+}
+
+static int end_io_acct(struct dm_io *io)
+{
+        struct mapped_device *md = io->md;
+        struct bio *bio = io->bio;
+        unsigned long duration = jiffies - io->start_time;
+        int pending;
+        int rw = bio_data_dir(bio);
+
+        preempt_disable();
+        disk_round_stats(dm_disk(md));
+        preempt_enable();
+        dm_disk(md)->in_flight = pending = atomic_dec_return(&md->pending);
+
+        disk_stat_add(dm_disk(md), ticks[rw], duration);
+
+        return !pending;
+}
+
 /*
  * Add the bio to the list of deferred io.
  */
@@ -299,7 +330,7 @@ static void dec_pending(struct dm_io *io, int error)
                 io->error = error;
 
         if (atomic_dec_and_test(&io->io_count)) {
-                if (atomic_dec_and_test(&io->md->pending))
+                if (end_io_acct(io))
                         /* nudge anyone waiting on suspend queue */
                         wake_up(&io->md->wait);
 
@@ -554,7 +585,7 @@ static void __split_bio(struct mapped_device *md, struct bio *bio)
         ci.sector_count = bio_sectors(bio);
         ci.idx = bio->bi_idx;
 
-        atomic_inc(&md->pending);
+        start_io_acct(ci.io);
         while (ci.sector_count)
                 __clone_and_map(&ci);