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

[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@google.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 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

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

[Eric Dumazet]

On Thu, Feb 15, 2024 at 12:28 PM Breno Leitao <leitao@debian.org> wrote:
>
> 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@google.com>
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  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)

  const struct net_device *dev

> +{
> +       if (dev->features & NETIF_F_LLTX ||
> +           dev->priv_flags & IFF_NO_QUEUE)
> +               return false;
> +
> +       return true;
> +}
> +
>

Thanks.

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

[Breno Leitao]

On Thu, Feb 15, 2024 at 01:47:47PM +0100, Eric Dumazet wrote:
> On Thu, Feb 15, 2024 at 12:28 PM Breno Leitao <leitao@debian.org> wrote:
> >
> > 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@google.com>
> > Signed-off-by: Breno Leitao <leitao@debian.org>
> > ---
> >  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)
> 
>   const struct net_device *dev

Thanks. I will update and incorporate it in a v2 (that I am planning to
send tomorrow).

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

[Jakub Kicinski]

On Thu, 15 Feb 2024 03:27:27 -0800 Breno Leitao wrote:
> 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

I'm tempted to also get rid of the #ifdefs while at it.

> +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;

make this
	return IS_ENABLED(CONFIG_BQL);

And throw in something like:

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index a09d507c5b03..119075dff0ee 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1454,6 +1454,9 @@ static const struct attribute_group dql_group = {
        .name  = "byte_queue_limits",
        .attrs  = dql_attrs,
 };
+#else
+/* Fake declaration, all the code using it should be dead */
+extern const struct attribute_group dql_group;
 #endif /* CONFIG_BQL */
 
 #ifdef CONFIG_XPS

You should then be able to remove the #ifdef CONFIG_BQL around the
uses of netdev_uses_bql(), compiler will realize it always returns
false and eliminate the code making use of &dql_group.