Subject: [PATCH] net: add sysfs attribute for enabling threaded NAPI
From: Felix Fietkau <[email-masked]>
Date: Fri, 21 Aug 2020 15:07:54 +0200

This can be used to enable threaded NAPI on drivers that did not explicitly
request it.

Suggested-by: Eric Dumazet <[email-masked]>
Signed-off-by: Felix Fietkau <[email-masked]>
---

--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -472,6 +472,52 @@ static ssize_t proto_down_store(struct d
 }
 NETDEVICE_SHOW_RW(proto_down, fmt_dec);
 
+static int change_napi_threaded(struct net_device *dev, unsigned long val)
+{
+	struct napi_struct *napi;
+
+	if (list_empty(&dev->napi_list))
+		return -EOPNOTSUPP;
+
+	list_for_each_entry(napi, &dev->napi_list, dev_list) {
+		if (val)
+			set_bit(NAPI_STATE_THREADED, &napi->state);
+		else
+			clear_bit(NAPI_STATE_THREADED, &napi->state);
+	}
+
+	return 0;
+}
+
+static ssize_t napi_threaded_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t len)
+{
+	return netdev_store(dev, attr, buf, len, change_napi_threaded);
+}
+
+static ssize_t napi_threaded_show(struct device *dev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	struct net_device *netdev = to_net_dev(dev);
+	struct napi_struct *napi;
+	bool enabled = false;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+
+	list_for_each_entry(napi, &netdev->napi_list, dev_list) {
+		if (test_bit(NAPI_STATE_THREADED, &napi->state))
+			enabled = true;
+	}
+
+	rtnl_unlock();
+
+	return sprintf(buf, fmt_dec, enabled);
+}
+static DEVICE_ATTR_RW(napi_threaded);
+
 static ssize_t phys_port_id_show(struct device *dev,
 				 struct device_attribute *attr, char *buf)
 {
@@ -564,6 +610,7 @@ static struct attribute *net_class_attrs
 	&dev_attr_tx_queue_len.attr,
 	&dev_attr_gro_flush_timeout.attr,
 	&dev_attr_napi_defer_hard_irqs.attr,
+	&dev_attr_napi_threaded.attr,
 	&dev_attr_phys_port_id.attr,
 	&dev_attr_phys_port_name.attr,
 	&dev_attr_phys_switch_id.attr,