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authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>2020-03-25 16:07:04 +0300
committerJens Axboe <axboe@kernel.dk>2020-03-25 17:49:08 +0300
commit2b8bd423614c595540eaadcfbc702afe8e155e50 (patch)
treece3476290a0299a42f6387915f62054271d1e4ee /block/blk-core.c
parent387048bf67eeff8bdf7c2a41b03b48230a88b3d3 (diff)
downloadlinux-2b8bd423614c595540eaadcfbc702afe8e155e50.tar.xz
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.c4
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();
}