[PATCH 2/4] nvme-tcp: align I/O cpu with blk-mq mapping

[Hannes Reinecke]

When 'wq_unbound' is selected we should select the
the first CPU from a given blk-mq hctx mapping to queue
the tcp workqueue item. With this we can instruct the
workqueue code to keep the I/O affinity and avoid
a performance penalty.

One should switch to 'cpu' workqueue affinity to
get full advantage of this by issuing:

echo cpu > /sys/devices/virtual/workqueue/nvme_tcp_wq_*/affinity_scope

Signed-off-by: Hannes Reinecke <hare at kernel.org>
---
 drivers/nvme/host/tcp.c | 44 +++++++++++++++++++++++++++++------------
 1 file changed, 31 insertions(+), 13 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index d43099c562fc..df184004a514 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -1559,19 +1559,36 @@ static bool nvme_tcp_poll_queue(struct nvme_tcp_queue *queue)
 static void nvme_tcp_set_queue_io_cpu(struct nvme_tcp_queue *queue)
 {
 	struct nvme_tcp_ctrl *ctrl = queue->ctrl;
-	int qid = nvme_tcp_queue_id(queue);
+	struct blk_mq_tag_set *set = &ctrl->tag_set;
+	int qid = nvme_tcp_queue_id(queue) - 1;
+	unsigned int *mq_map = NULL;;
 	int n = 0;
 
-	if (nvme_tcp_default_queue(queue))
-		n = qid - 1;
-	else if (nvme_tcp_read_queue(queue))
-		n = qid - ctrl->io_queues[HCTX_TYPE_DEFAULT] - 1;
-	else if (nvme_tcp_poll_queue(queue))
+	if (nvme_tcp_default_queue(queue)) {
+		mq_map = set->map[HCTX_TYPE_DEFAULT].mq_map;
+		n = qid;
+	} else if (nvme_tcp_read_queue(queue)) {
+		mq_map = set->map[HCTX_TYPE_READ].mq_map;
+		n = qid - ctrl->io_queues[HCTX_TYPE_DEFAULT];
+	} else if (nvme_tcp_poll_queue(queue)) {
+		mq_map = set->map[HCTX_TYPE_POLL].mq_map;
 		n = qid - ctrl->io_queues[HCTX_TYPE_DEFAULT] -
-				ctrl->io_queues[HCTX_TYPE_READ] - 1;
-	if (wq_unbound)
-		queue->io_cpu = WORK_CPU_UNBOUND;
-	else
+				ctrl->io_queues[HCTX_TYPE_READ];
+	}
+	if (wq_unbound) {
+		int cpu;
+
+		if (WARN_ON(!mq_map))
+			return;
+		for_each_online_cpu(cpu) {
+			if (mq_map[cpu] == qid) {
+				queue->io_cpu = cpu;
+				break;
+			}
+		}
+		dev_dbg(ctrl->ctrl.device, "queue %d: using cpu %d\n",
+			qid, queue->io_cpu);
+	} else
 		queue->io_cpu = cpumask_next_wrap(n - 1, cpu_online_mask, -1, false);
 }
 
@@ -1716,7 +1733,7 @@ static int nvme_tcp_alloc_queue(struct nvme_ctrl *nctrl, int qid,
 
 	queue->sock->sk->sk_allocation = GFP_ATOMIC;
 	queue->sock->sk->sk_use_task_frag = false;
-	nvme_tcp_set_queue_io_cpu(queue);
+	queue->io_cpu = WORK_CPU_UNBOUND;
 	queue->request = NULL;
 	queue->data_remaining = 0;
 	queue->ddgst_remaining = 0;
@@ -1872,9 +1889,10 @@ static int nvme_tcp_start_queue(struct nvme_ctrl *nctrl, int idx)
 	nvme_tcp_init_recv_ctx(queue);
 	nvme_tcp_setup_sock_ops(queue);
 
-	if (idx)
+	if (idx) {
+		nvme_tcp_set_queue_io_cpu(queue);
 		ret = nvmf_connect_io_queue(nctrl, idx);
-	else
+	} else
 		ret = nvmf_connect_admin_queue(nctrl);
 
 	if (!ret) {
-- 
2.35.3