[PATCH net-next] net: sysfs: Do not create sysfs for non BQL device

[Breno Leitao]

Creation of sysfs entries is expensive, mainly for workloads that
constantly creates netdev and netns often.

Do not create BQL sysfs entries for devices that don't need,
basically those that do not have a real queue, i.e, devices that has
NETIF_F_LLTX and IFF_NO_QUEUE, such as `lo` interface.

This will remove the /sys/class/net/eth0/queues/tx-X/byte_queue_limits/
directory for these devices.

In the example below, eth0 has the `byte_queue_limits` directory but not
`lo`.

	# ls /sys/class/net/lo/queues/tx-0/
	traffic_class  tx_maxrate  tx_timeout  xps_cpus  xps_rxqs

	# ls /sys/class/net/eth0/queues/tx-0/byte_queue_limits/
	hold_time  inflight  limit  limit_max  limit_min

Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
 net/core/net-sysfs.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index a09d507c5b03..c79bc11a0347 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1417,6 +1417,15 @@ static ssize_t bql_show_inflight(struct netdev_queue *queue,
 	return sysfs_emit(buf, "%u\n", dql->num_queued - dql->num_completed);
 }
 
+static bool netdev_uses_bql(struct net_device *dev)
+{
+	if (dev->features & NETIF_F_LLTX ||
+	    dev->priv_flags & IFF_NO_QUEUE)
+		return false;
+
+	return true;
+}
+
 static struct netdev_queue_attribute bql_inflight_attribute __ro_after_init =
 	__ATTR(inflight, 0444, bql_show_inflight, NULL);
 
@@ -1709,9 +1718,11 @@ static int netdev_queue_add_kobject(struct net_device *dev, int index)
 		goto err;
 
 #ifdef CONFIG_BQL
-	error = sysfs_create_group(kobj, &dql_group);
-	if (error)
-		goto err;
+	if (netdev_uses_bql(dev)) {
+		error = sysfs_create_group(kobj, &dql_group);
+		if (error)
+			goto err;
+	}
 #endif
 
 	kobject_uevent(kobj, KOBJ_ADD);
@@ -1734,7 +1745,8 @@ static int tx_queue_change_owner(struct net_device *ndev, int index,
 		return error;
 
 #ifdef CONFIG_BQL
-	error = sysfs_group_change_owner(kobj, &dql_group, kuid, kgid);
+	if (netdev_uses_bql(ndev))
+		error = sysfs_group_change_owner(kobj, &dql_group, kuid, kgid);
 #endif
 	return error;
 }
@@ -1768,7 +1780,8 @@ netdev_queue_update_kobjects(struct net_device *dev, int old_num, int new_num)
 		if (!refcount_read(&dev_net(dev)->ns.count))
 			queue->kobj.uevent_suppress = 1;
 #ifdef CONFIG_BQL
-		sysfs_remove_group(&queue->kobj, &dql_group);
+		if (netdev_uses_bql(dev))
+			sysfs_remove_group(&queue->kobj, &dql_group);
 #endif
 		kobject_put(&queue->kobj);
 	}
-- 
2.39.3