On Wed, Aug 16, 2023 at 09:27:08AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Currently, 'carryover_ios/bytes' is not handled in throtl_trim_slice(),
> for consequence, 'carryover_ios/bytes' will be used to throttle bio
> multiple times, for example:
>
> 1) set iops limit to 100, and slice start is 0, slice end is 100ms;
> 2) current time is 0, and 10 ios are dispatched, those io won't be
> throttled and io_disp is 10;
> 3) still at current time 0, update iops limit to 1000, carryover_ios is
> updated to (0 - 10) = -10;
> 4) in this slice(0 - 100ms), io_allowed = 100 + (-10) = 90, which means
> only 90 ios can be dispatched without waiting;
> 5) assume that io is throttled in slice(0 - 100ms), and
> throtl_trim_slice() update silce to (100ms - 200ms). In this case,
> 'carryover_ios/bytes' is not cleared and still only 90 ios can be
> dispatched between 100ms - 200ms.
>
> Fix this problem by updating 'carryover_ios/bytes' in
> throtl_trim_slice().
>
> Fixes: a880ae93e5b5 ("blk-throttle: fix io hung due to configuration updates")
> Reported-by: zhuxiaohui <zhuxiaohui.400@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/all/20230812072116.42321-1-zhuxiaohui.400@xxxxxxxxxxxxx/
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Thanks.
--
tejun
