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authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>2020-03-25 14:07:04 +0100
committerJens Axboe <axboe@kernel.dk>2020-03-25 15:49:08 +0100
commit2b8bd423614c595540eaadcfbc702afe8e155e50 (patch)
treece3476290a0299a42f6387915f62054271d1e4ee /fs/cachefiles
parentblock: merge partition-generic.c and check.c (diff)
downloadlinux-2b8bd423614c595540eaadcfbc702afe8e155e50.tar.xz
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>
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