[PATCH 2/3] nvme-tcp: align I/O cpu with blk-mq mapping

[Hannes Reinecke]

We should align the 'io_cpu' setting with the blk-mq
cpu mapping to ensure that we're not bouncing threads
when doing I/O. To avoid cpu contention this patch also
adds an atomic counter for the number of queues on each
cpu to distribute the load across all CPUs in the blk-mq cpu set.
Additionally we should always set the 'io_cpu' value, as
in the WQ_UNBOUND case it'll be treated as a hint anyway.

Performance comparison:
               baseline rx/tx    blk-mq align
4k seq write:  449MiB/s 480MiB/s 524MiB/s
4k rand write: 410MiB/s 481MiB/s 524MiB/s
4k seq read:   478MiB/s 481MiB/s 566MiB/s
4k rand read:  547MiB/s 480MiB/s 511MiB/s

Signed-off-by: Hannes Reinecke <hare at kernel.org>
---
 drivers/nvme/host/tcp.c | 65 +++++++++++++++++++++++++++++++----------
 1 file changed, 49 insertions(+), 16 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index f621d3ba89b2..a5c42a7b4bee 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -26,6 +26,8 @@
 
 struct nvme_tcp_queue;
 
+static atomic_t nvme_tcp_cpu_queues[NR_CPUS];
+
 /* Define the socket priority to use for connections were it is desirable
  * that the NIC consider performing optimized packet processing or filtering.
  * A non-zero value being sufficient to indicate general consideration of any
@@ -1578,20 +1580,42 @@ 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);
-	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))
+	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, cpu, io_cpu, min_queues = WORK_CPU_UNBOUND;
+
+	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
-		queue->io_cpu = cpumask_next_wrap(n - 1, cpu_online_mask, -1, false);
+				ctrl->io_queues[HCTX_TYPE_READ];
+	}
+
+	if (WARN_ON(!mq_map))
+		return;
+	for_each_online_cpu(cpu) {
+		int num_queues;
+
+		if (mq_map[cpu] != qid)
+			continue;
+		num_queues = atomic_read(&nvme_tcp_cpu_queues[cpu]);
+		if (num_queues < min_queues) {
+			min_queues = num_queues;
+			io_cpu = cpu;
+		}
+	}
+	if (io_cpu != queue->io_cpu) {
+		queue->io_cpu = io_cpu;
+		atomic_inc(&nvme_tcp_cpu_queues[io_cpu]);
+	}
+	dev_dbg(ctrl->ctrl.device, "queue %d: using cpu %d\n",
+		qid, queue->io_cpu);
 }
 
 static void nvme_tcp_tls_done(void *data, int status, key_serial_t pskid)
@@ -1735,7 +1759,7 @@ 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;
@@ -1847,6 +1871,10 @@ static void __nvme_tcp_stop_queue(struct nvme_tcp_queue *queue)
 	kernel_sock_shutdown(queue->sock, SHUT_RDWR);
 	nvme_tcp_restore_sock_ops(queue);
 	cancel_work_sync(&queue->io_work);
+	if (queue->io_cpu != WORK_CPU_UNBOUND) {
+		atomic_dec(&nvme_tcp_cpu_queues[queue->io_cpu]);
+		queue->io_cpu = WORK_CPU_UNBOUND;
+	}
 }
 
 static void nvme_tcp_stop_queue(struct nvme_ctrl *nctrl, int qid)
@@ -1891,9 +1919,10 @@ 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) {
@@ -2920,6 +2949,7 @@ static struct nvmf_transport_ops nvme_tcp_transport = {
 static int __init nvme_tcp_init_module(void)
 {
 	unsigned int wq_flags = WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_SYSFS;
+	int cpu;
 
 	BUILD_BUG_ON(sizeof(struct nvme_tcp_hdr) != 8);
 	BUILD_BUG_ON(sizeof(struct nvme_tcp_cmd_pdu) != 72);
@@ -2937,6 +2967,9 @@ static int __init nvme_tcp_init_module(void)
 	if (!nvme_tcp_wq)
 		return -ENOMEM;
 
+	for_each_possible_cpu(cpu)
+		atomic_set(&nvme_tcp_cpu_queues[cpu], 0);
+
 	nvmf_register_transport(&nvme_tcp_transport);
 	return 0;
 }
-- 
2.35.3