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

On Mon, Apr 19, 2021 at 07:51:34AM +0200, Gioh Kim wrote:

On Mon, Apr 19, 2021 at 7:46 AM Leon Romanovsky [off-list ref] wrote:

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On Mon, Apr 19, 2021 at 07:12:09AM +0200, Gioh Kim wrote:

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On Sun, Apr 18, 2021 at 10:36 AM Leon Romanovsky [off-list ref] wrote:

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On Wed, Apr 14, 2021 at 02:23:56PM +0200, Gioh Kim wrote:

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From: Gioh Kim <redacted>

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

<...>

I am sorry that I don't understand exactly.
Do I need to change them to "con<5..8>"?

No, I just removed not relevant text and replaced it with <...> in
automatic way :).

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+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.

Ah, ok. So you mean,
1. remove unlikely from that line
2. send a patch to remove all likely/unlikely for next round

Am I right?

Right