On Wed, Jan 03, 2024 at 03:15:15PM +0800, Yu Kuai wrote: > From: Yu Kuai <yukuai3@xxxxxxxxxx> > > Currently, io_ticks is accounted based on sampling, specifically > update_io_ticks() will always account io_ticks by 1 jiffies from > bdev_start_io_acct()/blk_account_io_start(), and the result can be > inaccurate, for example(HZ is 250): > > Test script: > fio -filename=/dev/sda -bs=4k -rw=write -direct=1 -name=test -thinktime=4ms > > Test result: util is about 90%, while the disk is really idle. > > In order to account io_ticks precisely, update_io_ticks() must know if > there are IO inflight already, and this requires overhead slightly, > hence precise io accounting is disabled by default, and user can enable > it through sysfs entry. > > Noted that for rq-based devcie, part_stat_local_inc/dec() and > part_in_flight() is used to track inflight instead of iterating tags, > which is not supposed to be used in fast path because 'tags->lock' is > grabbed in blk_mq_find_and_get_req(). > > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx> > --- > Changes in v2: > - remove the new parameter for update_io_ticks(); > - simplify update_io_ticks(); > - use swith in queue_iostats_store(); > - add missing part_stat_local_dec() in blk_account_io_merge_request() Looks fine, Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> thanks, Ming
