Re: [PATCHv4 for-next 13/19] block/rnbd-clt: Support polling mode for IO latency optimization

[Leon Romanovsky <leon@kernel.org>]

On Mon, Apr 19, 2021 at 07:12:09AM +0200, Gioh Kim wrote:
> On Sun, Apr 18, 2021 at 10:36 AM Leon Romanovsky <leon@kernel.org> wrote:
> >
> > On Wed, Apr 14, 2021 at 02:23:56PM +0200, Gioh Kim wrote:
> > > From: Gioh Kim <gi-oh.kim@cloud.ionos.com>
> > >
> > > RNBD can make double-queues for irq-mode and poll-mode.
> > > For example, on 4-CPU system 8 request-queues are created,
> > > 4 for irq-mode and 4 for poll-mode.
> > > If the IO has HIPRI flag, the block-layer will call .poll function
> > > of RNBD. Then IO is sent to the poll-mode queue.
> > > Add optional nr_poll_queues argument for map_devices interface.
> > >
> > > To support polling of RNBD, RTRS client creates connections
> > > for both of irq-mode and direct-poll-mode.
> > >
> > > For example, on 4-CPU system it could've create 5 connections:
> > > con[0] => user message (softirq cq)
> > > con[1:4] => softirq cq
> > >
> > > After this patch, it can create 9 connections:
> > > con[0] => user message (softirq cq)
> > > con[1:4] => softirq cq
> > > con[5:8] => DIRECT-POLL cq

<...>

> > > +int rtrs_clt_rdma_cq_direct(struct rtrs_clt *clt, unsigned int index)
> > > +{
> > > +     int cnt;
> > > +     struct rtrs_con *con;
> > > +     struct rtrs_clt_sess *sess;
> > > +     struct path_it it;
> > > +
> > > +     rcu_read_lock();
> > > +     for (path_it_init(&it, clt);
> > > +          (sess = it.next_path(&it)) && it.i < it.clt->paths_num; it.i++) {
> > > +             if (unlikely(READ_ONCE(sess->state) != RTRS_CLT_CONNECTED))
> >
> > We talked about useless likely/unlikely in your workloads.
> 
> Right, I've made a patch to remove all likely/unlikely
> and will send with the next patch set.

This specific line is "brand new". We don't add code that will be
removed in next patch.

Thanks