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| author |   Konstantin Khlebnikov <khlebnikov@yandex-team.ru> | 2020-03-25 16:07:04 +0300 |
|---|---|---|
| committer |   Jens Axboe <axboe@kernel.dk> | 2020-03-25 08:49:08 -0600 |
| commit | 2b8bd423614c595540eaadcfbc702afe8e155e50 (patch) | |
| tree | ce3476290a0299a42f6387915f62054271d1e4ee /include/linux/genhd.h | |
| parent | block: merge partition-generic.c and check.c (diff) | |
| download | wireguard-linux-2b8bd423614c595540eaadcfbc702afe8e155e50.tar.xz wireguard-linux-2b8bd423614c595540eaadcfbc702afe8e155e50.zip | |
block/diskstats: more accurate approximation of io_ticks for slow disks
Currently io_ticks is approximated by adding one at each start and end of
requests if jiffies counter has changed. This works perfectly for requests
shorter than a jiffy or if one of requests starts/ends at each jiffy.
If disk executes just one request at a time and they are longer than two
jiffies then only first and last jiffies will be accounted.
Fix is simple: at the end of request add up into io_ticks jiffies passed
since last update rather than just one jiffy.
Example: common HDD executes random read 4k requests around 12ms.
fio --name=test --filename=/dev/sdb --rw=randread --direct=1 --runtime=30 &
iostat -x 10 sdb
Note changes of iostat's "%util" 8,43% -> 99,99% before/after patch:
Before:
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sdb 0,00 0,00 82,60 0,00 330,40 0,00 8,00 0,96 12,09 12,09 0,00 1,02 8,43
After:
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sdb 0,00 0,00 82,50 0,00 330,00 0,00 8,00 1,00 12,10 12,10 0,00 12,12 99,99
Now io_ticks does not loose time between start and end of requests, but
for queue-depth > 1 some I/O time between adjacent starts might be lost.
For load estimation "%util" is not as useful as average queue length,
but it clearly shows how often disk queue is completely empty.
Fixes: 5b18b5a73760 ("block: delete part_round_stats and switch to less precise counting")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/genhd.h')
| -rw-r--r-- | include/linux/genhd.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/genhd.h b/include/linux/genhd.h index da62b44b15be..13bb51f37b3f 100644 --- a/include/linux/genhd.h +++ b/include/linux/genhd.h @@ -422,7 +422,7 @@ void part_dec_in_flight(struct request_queue *q, struct hd_struct *part, void part_inc_in_flight(struct request_queue *q, struct hd_struct *part, int rw); -void update_io_ticks(struct hd_struct *part, unsigned long now); +void update_io_ticks(struct hd_struct *part, unsigned long now, bool end); /* block/genhd.c */ extern void device_add_disk(struct device *parent, struct gendisk *disk, |