[LSF/MM TOPIC][LSF/MM ATTEND] NAPI polling for block drivers

[Sagi Grimberg]

> Hannes just spotted this:
> static int nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
>                          const struct blk_mq_queue_data *bd)
> {
> [...]
>         __nvme_submit_cmd(nvmeq, &cmnd);
>         nvme_process_cq(nvmeq);
>         spin_unlock_irq(&nvmeq->q_lock);
>         return BLK_MQ_RQ_QUEUE_OK;
> out_cleanup_iod:
>         nvme_free_iod(dev, req);
> out_free_cmd:
>         nvme_cleanup_cmd(req);
>         return ret;
> }
>
> So we're draining the CQ on submit. This of cause makes polling for
> completions in the IRQ handler rather pointless as we already did in the
> submission path.

I think you missed:
http://git.infradead.org/nvme.git/commit/49c91e3e09dc3c9dd1718df85112a8cce3ab7007