block: delete part_round_stats and switch to less precise counting

We want to convert to per-cpu in_flight counters.

The function part_round_stats needs the in_flight counter every jiffy, it
would be too costly to sum all the percpu variables every jiffy, so it
must be deleted. part_round_stats is used to calculate two counters -
time_in_queue and io_ticks.

time_in_queue can be calculated without part_round_stats, by adding the
duration of the I/O when the I/O ends (the value is almost as exact as the
previously calculated value, except that time for in-progress I/Os is not
counted).

io_ticks can be approximated by increasing the value when I/O is started
or ended and the jiffies value has changed. If the I/Os take less than a
jiffy, the value is as exact as the previously calculated value. If the
I/Os take more than a jiffy, io_ticks can drift behind the previously
calculated value.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 2 deletions

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 1677cd2a4c4e..838c2a7a40c5 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -398,8 +398,7 @@ static inline void free_part_info(struct hd_struct *part)
         kfree(part->info);
 }
 
-/* block/blk-core.c */
-extern void part_round_stats(struct request_queue *q, struct hd_struct *part);
+void update_io_ticks(struct hd_struct *part, unsigned long now);
 
 /* block/genhd.c */
 extern void device_add_disk(struct device *parent, struct gendisk *disk,