[dm-devel] [PATCH v3 09/11] dm: support IO polling for bio-based dm device

[Ming Lei]

On Mon, Feb 08, 2021 at 04:52:41PM +0800, Jeffle Xu wrote:
> DM will iterate and poll all polling hardware queues of all target mq
> devices when polling IO for dm device. To mitigate the race introduced
> by iterating all target hw queues, a per-hw-queue flag is maintained

What is the per-hw-queue flag?

> to indicate whether this polling hw queue currently being polled on or
> not. Every polling hw queue is exclusive to one polling instance, i.e.,
> the polling instance will skip this polling hw queue if this hw queue
> currently is being polled by another polling instance, and start
> polling on the next hw queue.

Not see such skip in dm_poll_one_dev() in which
queue_for_each_poll_hw_ctx() is called directly for polling all POLL
hctxs of the request queue, so can you explain it a bit more about this
skip mechanism?

Even though such skipping is implemented, not sure if good performance
can be reached because hctx poll may be done in ping-pong style
among several CPUs. But blk-mq hctx is supposed to have its cpu affinities.

-- 
Ming