Tejun Heo wrote on 2021/7/27 5:46:

Hello,

On Tue, Jul 20, 2021 at 12:35:54AM +0800, brookxu wrote:

quoted

In order to avoid code duplication and IOPS stability problems caused by estimating
the equivalent number of IOs, and to avoid potential deadlock problems caused by
synchronization through queue_lock. I tried to count the number of splited IOs in
the current window through two atomic counters. Add the value of the atomic variable
when calculating io_disp[rw], which can also avoid the problem of inaccurate IOPS in
large IO scenarios. How do you think of this approach? Thanks for your time.

I guess it's okay but am still not a big fan of adding another hook. This is
primarily because blk-throtl is sitting too early in the stack - e.g. rq_qos
is doing the same thing but sits after the split path - and it's a bit nasty
to add an additional hook for it.

Do you think it can be an option to relocate the blk-throtl hooks to the
same spots as rq-qos or, even better, make it use rq-qos?

Make blk-throttle use rq-qos may be more elegant. But I found that there may be at least
one problem that is difficult to solve. blk-throttle supports separate throttle for read
and write IOs, which means that we cannot suspend tasks during throttle, but rq-qos
throttle IOs by suspending tasks.

We may be able to relocate the blk-throttle hooks to the rq-qos hooks. Since we may not
be able to replace the throttle hook, in this case, if we register a rq-qos to the system,
part of the blk-throttle hooks is in rq-qos and part hooks not, which feels a bit confusing.
In addition, we may need to implement more hooks, such as IO merge hook.

Thanks for you time.

Thanks.