Re: [PATCH RFC 1/3] block/mq-deadline: Revert "block/mq-deadline: Fix the tag reservation code"

[Yu Kuai]

Hi, Bart

在 2024/12/11 4:33, Bart Van Assche 写道:
> > If so, following are the options that I can think of to fix this:
> >
> > 1) make async_depth read-only, if 75% tags will hurt performance in some
> > cases, user can increase nr_requests to prevent it.
> > 2) refactor elevator sysfs api, remove eq->sysfs_lock and replace it
> > with q->sysfs_lock, so deadline_async_depth_store() will be protected
> > against changing hctxs, and min_shallow_depth can be updated here.
> > 3) other options?
>
> Another option is to remove the ability to configure async_depth. If it
> is too much trouble to get the implementation right without causing
> regressions for existing workloads, one possibility is to remove support
> for restricting the number of asynchronous requests in flight.

If you agree, I'll use following option in the next version:

4) set min_async_depth to 64 (after treating min_shallow_depth for the
whole sbitmap instead of one word).

The good thing is that user can still set async_depth without changing
wake_batch, the side effect is that async_depth can't be used if
nr_requests <= 64;

Thanks,
Kuai