Re: [PATCH 1/4] block: add scalable completion tracking of requests

[Christoph Hellwig]

On Tue, Nov 01, 2016 at 03:05:22PM -0600, Jens Axboe wrote:
> For legacy block, we simply track them in the request queue. For
> blk-mq, we track them on a per-sw queue basis, which we can then
> sum up through the hardware queues and finally to a per device
> state.

what is the use case for the legacy request tracking?