[PATCH v2 1/2] blk-mq: add tagset quiesce interface

[Christoph Hellwig]

On Mon, Oct 17, 2022 at 03:39:06PM +0200, Christoph Hellwig wrote:
> Having to allocate a struct rcu_synchronize for each of the potentially
> many queues here is a bit sad.
> 
> Pull just explained the start_poll_synchronize_rcu interfaces at ALPSS
> last week, so I wonder if something like that would also be feasible
> for SRCU, as that would come in really handy here.

Alternatively I wonder if we could simply use a single srcu_struct
in the tag_set instead of one per-queue.  That would potentially
increase the number of read side critical sections
blk_mq_wait_quiesce_done would have to wait for in tagsets with
multiple queues, but I wonder how much overhead that would be in
practive.