[RFC PATCH 1/4] nvme-tcp: optionally limit I/O queue count based on NIC queues
Nilay Shroff
nilay at linux.ibm.com
Mon Apr 20 04:49:33 PDT 2026
NVMe-TCP currently provisions I/O queues primarily based on CPU
availability. On systems where the number of CPUs significantly exceeds
the number of NIC hardware queues, this can lead to multiple I/O queues
sharing the same NIC TX/RX queues, resulting in increased lock
contention, cacheline bouncing, and inter-processor interrupts (IPIs).
In such configurations, limiting the number of NVMe-TCP I/O queues to
the number of NIC hardware queues can improve performance by reducing
contention and improving locality. Aligning NVMe-TCP worker threads with
NIC queue topology may also help reduce tail latency.
Add a new transport option "match_hw_queues" to allow users to
optionally limit the number of NVMe-TCP I/O queues to the number of NIC
TX/RX queues. When enabled, the number of I/O queues is set to:
min(num_online_cpus, num_nic_queues)
This behavior is opt-in and does not change existing defaults.
Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
---
drivers/nvme/host/fabrics.c | 4 ++
drivers/nvme/host/fabrics.h | 3 +
drivers/nvme/host/tcp.c | 120 +++++++++++++++++++++++++++++++++++-
3 files changed, 126 insertions(+), 1 deletion(-)
diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index ac3d4f400601..62ae998825e1 100644
--- a/drivers/nvme/host/fabrics.c
+++ b/drivers/nvme/host/fabrics.c
@@ -709,6 +709,7 @@ static const match_table_t opt_tokens = {
{ NVMF_OPT_TLS, "tls" },
{ NVMF_OPT_CONCAT, "concat" },
#endif
+ { NVMF_OPT_MATCH_HW_QUEUES, "match_hw_queues" },
{ NVMF_OPT_ERR, NULL }
};
@@ -1064,6 +1065,9 @@ static int nvmf_parse_options(struct nvmf_ctrl_options *opts,
}
opts->concat = true;
break;
+ case NVMF_OPT_MATCH_HW_QUEUES:
+ opts->match_hw_queues = true;
+ break;
default:
pr_warn("unknown parameter or missing value '%s' in ctrl creation request\n",
p);
diff --git a/drivers/nvme/host/fabrics.h b/drivers/nvme/host/fabrics.h
index caf5503d0833..e8e3a2672832 100644
--- a/drivers/nvme/host/fabrics.h
+++ b/drivers/nvme/host/fabrics.h
@@ -67,6 +67,7 @@ enum {
NVMF_OPT_KEYRING = 1 << 26,
NVMF_OPT_TLS_KEY = 1 << 27,
NVMF_OPT_CONCAT = 1 << 28,
+ NVMF_OPT_MATCH_HW_QUEUES = 1 << 29,
};
/**
@@ -106,6 +107,7 @@ enum {
* @disable_sqflow: disable controller sq flow control
* @hdr_digest: generate/verify header digest (TCP)
* @data_digest: generate/verify data digest (TCP)
+ * @match_hw_queues: limit controller IO queue count based on NIC queues (TCP)
* @nr_write_queues: number of queues for write I/O
* @nr_poll_queues: number of queues for polling I/O
* @tos: type of service
@@ -136,6 +138,7 @@ struct nvmf_ctrl_options {
bool disable_sqflow;
bool hdr_digest;
bool data_digest;
+ bool match_hw_queues;
unsigned int nr_write_queues;
unsigned int nr_poll_queues;
int tos;
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 243dab830dc8..7102a7a54d78 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -16,6 +16,8 @@
#include <net/tls.h>
#include <net/tls_prot.h>
#include <net/handshake.h>
+#include <net/ip6_route.h>
+#include <linux/in6.h>
#include <linux/blk-mq.h>
#include <net/busy_poll.h>
#include <trace/events/sock.h>
@@ -1762,6 +1764,103 @@ static int nvme_tcp_start_tls(struct nvme_ctrl *nctrl,
return ret;
}
+static struct net_device *nvme_tcp_get_netdev(struct nvme_ctrl *ctrl)
+{
+ struct net_device *dev = NULL;
+
+ if (ctrl->opts->mask & NVMF_OPT_HOST_IFACE)
+ dev = dev_get_by_name(&init_net, ctrl->opts->host_iface);
+ else {
+ struct nvme_tcp_ctrl *tctrl = to_tcp_ctrl(ctrl);
+
+ if (tctrl->addr.ss_family == AF_INET) {
+ struct rtable *rt;
+ struct flowi4 fl4 = {};
+ struct sockaddr_in *addr =
+ (struct sockaddr_in *)&tctrl->addr;
+
+ fl4.daddr = addr->sin_addr.s_addr;
+ if (ctrl->opts->mask & NVMF_OPT_HOST_TRADDR) {
+ addr = (struct sockaddr_in *)&tctrl->src_addr;
+ fl4.saddr = addr->sin_addr.s_addr;
+ }
+ fl4.flowi4_proto = IPPROTO_TCP;
+
+ rt = ip_route_output_key(&init_net, &fl4);
+ if (IS_ERR(rt))
+ return NULL;
+
+ dev = dst_dev(&rt->dst);
+ /*
+ * Get reference to netdev as ip_rt_put() will
+ * release the netdev reference.
+ */
+ if (dev)
+ dev_hold(dev);
+
+ ip_rt_put(rt);
+
+ } else if (tctrl->addr.ss_family == AF_INET6) {
+ struct dst_entry *dst;
+ struct flowi6 fl6 = {};
+ struct sockaddr_in6 *addr6 =
+ (struct sockaddr_in6 *)&tctrl->addr;
+
+ fl6.daddr = addr6->sin6_addr;
+ if (ctrl->opts->mask & NVMF_OPT_HOST_TRADDR) {
+ addr6 = (struct sockaddr_in6 *)&tctrl->src_addr;
+ fl6.saddr = addr6->sin6_addr;
+ }
+ fl6.flowi6_proto = IPPROTO_TCP;
+
+ dst = ip6_route_output(&init_net, NULL, &fl6);
+ if (dst->error) {
+ dst_release(dst);
+ return NULL;
+ }
+
+ dev = dst_dev(dst);
+ /*
+ * Get reference to netdev as dst_release() will
+ * release the netdev reference.
+ */
+ if (dev)
+ dev_hold(dev);
+
+ dst_release(dst);
+ }
+ }
+
+ return dev;
+}
+
+static void nvme_tcp_put_netdev(struct net_device *dev)
+{
+ if (dev)
+ dev_put(dev);
+}
+
+/*
+ * Returns number of active NIC queues (min of TX/RX), or 0 if device cannot
+ * be determined.
+ */
+static int nvme_tcp_get_netdev_current_queue_count(struct nvme_ctrl *ctrl)
+{
+ struct net_device *dev;
+ int tx_queues, rx_queues;
+
+ dev = nvme_tcp_get_netdev(ctrl);
+ if (!dev)
+ return 0;
+
+ tx_queues = dev->real_num_tx_queues;
+ rx_queues = dev->real_num_rx_queues;
+
+ nvme_tcp_put_netdev(dev);
+
+ return min(tx_queues, rx_queues);
+}
+
static int nvme_tcp_alloc_queue(struct nvme_ctrl *nctrl, int qid,
key_serial_t pskid)
{
@@ -2144,6 +2243,24 @@ static int nvme_tcp_alloc_io_queues(struct nvme_ctrl *ctrl)
unsigned int nr_io_queues;
int ret;
+ if (!(ctrl->opts->mask & NVMF_OPT_NR_IO_QUEUES) &&
+ (ctrl->opts->mask & NVMF_OPT_MATCH_HW_QUEUES)) {
+ int nr_hw_queues;
+
+ nr_hw_queues = nvme_tcp_get_netdev_current_queue_count(ctrl);
+ if (nr_hw_queues <= 0)
+ goto init_queue;
+
+ ctrl->opts->nr_io_queues = min(nr_hw_queues, num_online_cpus());
+
+ if (ctrl->opts->nr_io_queues < num_online_cpus())
+ dev_info(ctrl->device,
+ "limiting I/O queues to %u (NIC queues %d, CPUs %u)\n",
+ ctrl->opts->nr_io_queues, nr_hw_queues,
+ num_online_cpus());
+ }
+
+init_queue:
nr_io_queues = nvmf_nr_io_queues(ctrl->opts);
ret = nvme_set_queue_count(ctrl, &nr_io_queues);
if (ret)
@@ -3019,7 +3136,8 @@ static struct nvmf_transport_ops nvme_tcp_transport = {
NVMF_OPT_HDR_DIGEST | NVMF_OPT_DATA_DIGEST |
NVMF_OPT_NR_WRITE_QUEUES | NVMF_OPT_NR_POLL_QUEUES |
NVMF_OPT_TOS | NVMF_OPT_HOST_IFACE | NVMF_OPT_TLS |
- NVMF_OPT_KEYRING | NVMF_OPT_TLS_KEY | NVMF_OPT_CONCAT,
+ NVMF_OPT_KEYRING | NVMF_OPT_TLS_KEY |
+ NVMF_OPT_CONCAT | NVMF_OPT_MATCH_HW_QUEUES,
.create_ctrl = nvme_tcp_create_ctrl,
};
--
2.53.0
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