diff options
| 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 /block/blk-core.c | |
| parent | 387048bf67eeff8bdf7c2a41b03b48230a88b3d3 (diff) | |
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 'block/blk-core.c')
| -rw-r--r-- | block/blk-core.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/block/blk-core.c b/block/blk-core.c index abfdcf81a228..4401b30a1751 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1337,7 +1337,7 @@ void blk_account_io_done(struct request *req, u64 now) part_stat_lock(); part = req->part; - update_io_ticks(part, jiffies); + update_io_ticks(part, jiffies, true); part_stat_inc(part, ios[sgrp]); part_stat_add(part, nsecs[sgrp], now - req->start_time_ns); part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns)); @@ -1379,7 +1379,7 @@ void blk_account_io_start(struct request *rq, bool new_io) rq->part = part; } - update_io_ticks(part, jiffies); + update_io_ticks(part, jiffies, false); part_stat_unlock(); } |