Commit 5fdd2f0e authored by Wei Wang's avatar Wei Wang Committed by David S. Miller
Browse files

net: add sysfs attribute to control napi threaded mode 



This patch adds a new sysfs attribute to the network device class.
Said attribute provides a per-device control to enable/disable the
threaded mode for all the napi instances of the given network device,
without the need for a device up/down.
User sets it to 1 or 0 to enable or disable threaded mode.
Note: when switching between threaded and the current softirq based mode
for a napi instance, it will not immediately take effect if the napi is
currently being polled. The mode switch will happen for the next time
napi_schedule() is called.

Co-developed-by: default avatarPaolo Abeni <pabeni@redhat.com>
Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
Co-developed-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Co-developed-by: default avatarFelix Fietkau <nbd@nbd.name>
Signed-off-by: default avatarFelix Fietkau <nbd@nbd.name>
Signed-off-by: default avatarWei Wang <weiwan@google.com>
Reviewed-by: default avatarAlexander Duyck <alexanderduyck@fb.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 29863d41

Documentation/ABI/testing/sysfs-class-net

+15 −0
Original line number Diff line number Diff line
@@ -337,3 +337,18 @@ Contact: netdev@vger.kernel.org 
Description:

		32-bit unsigned integer counting the number of times the link has

		been down



What:		/sys/class/net/<iface>/threaded

Date:		Jan 2021

KernelVersion:	5.12

Contact:	netdev@vger.kernel.org

Description:

		Boolean value to control the threaded mode per device. User could

		set this value to enable/disable threaded mode for all napi

		belonging to this device, without the need to do device up/down.



		Possible values:

		== ==================================

		0  threaded mode disabled for this dev

		1  threaded mode enabled for this dev

		== ==================================

include/linux/netdevice.h

+2 −0
Original line number Diff line number Diff line
@@ -497,6 +497,8 @@ static inline bool napi_complete(struct napi_struct *n) 
	return napi_complete_done(n, 0);

}



int dev_set_threaded(struct net_device *dev, bool threaded);



/**

 *	napi_disable - prevent NAPI from scheduling

 *	@n: NAPI context

net/core/dev.c

+46 −2
Original line number Diff line number Diff line
@@ -4291,8 +4291,9 @@ static inline void ____napi_schedule(struct softnet_data *sd, 


	if (test_bit(NAPI_STATE_THREADED, &napi->state)) {

		/* Paired with smp_mb__before_atomic() in

		 * napi_enable(). Use READ_ONCE() to guarantee

		 * a complete read on napi->thread. Only call

		 * napi_enable()/dev_set_threaded().

		 * Use READ_ONCE() to guarantee a complete

		 * read on napi->thread. Only call

		 * wake_up_process() when it's not NULL.

		 */

		thread = READ_ONCE(napi->thread);
@@ -6738,6 +6739,49 @@ static void init_gro_hash(struct napi_struct *napi) 
	napi->gro_bitmask = 0;

}



int dev_set_threaded(struct net_device *dev, bool threaded)

{

	struct napi_struct *napi;

	int err = 0;



	if (dev->threaded == threaded)

		return 0;



	if (threaded) {

		list_for_each_entry(napi, &dev->napi_list, dev_list) {

			if (!napi->thread) {

				err = napi_kthread_create(napi);

				if (err) {

					threaded = false;

					break;

				}

			}

		}

	}



	dev->threaded = threaded;



	/* Make sure kthread is created before THREADED bit

	 * is set.

	 */

	smp_mb__before_atomic();



	/* Setting/unsetting threaded mode on a napi might not immediately

	 * take effect, if the current napi instance is actively being

	 * polled. In this case, the switch between threaded mode and

	 * softirq mode will happen in the next round of napi_schedule().

	 * This should not cause hiccups/stalls to the live traffic.

	 */

	list_for_each_entry(napi, &dev->napi_list, dev_list) {

		if (threaded)

			set_bit(NAPI_STATE_THREADED, &napi->state);

		else

			clear_bit(NAPI_STATE_THREADED, &napi->state);

	}



	return err;

}



void netif_napi_add(struct net_device *dev, struct napi_struct *napi,

		    int (*poll)(struct napi_struct *, int), int weight)

{

net/core/net-sysfs.c

+40 −0
Original line number Diff line number Diff line
@@ -538,6 +538,45 @@ static ssize_t phys_switch_id_show(struct device *dev, 
}

static DEVICE_ATTR_RO(phys_switch_id);



static ssize_t threaded_show(struct device *dev,

			     struct device_attribute *attr, char *buf)

{

	struct net_device *netdev = to_net_dev(dev);

	ssize_t ret = -EINVAL;



	if (!rtnl_trylock())

		return restart_syscall();



	if (dev_isalive(netdev))

		ret = sprintf(buf, fmt_dec, netdev->threaded);



	rtnl_unlock();

	return ret;

}



static int modify_napi_threaded(struct net_device *dev, unsigned long val)

{

	int ret;



	if (list_empty(&dev->napi_list))

		return -EOPNOTSUPP;



	if (val != 0 && val != 1)

		return -EOPNOTSUPP;



	ret = dev_set_threaded(dev, val);



	return ret;

}



static ssize_t threaded_store(struct device *dev,

			      struct device_attribute *attr,

			      const char *buf, size_t len)

{

	return netdev_store(dev, attr, buf, len, modify_napi_threaded);

}

static DEVICE_ATTR_RW(threaded);



static struct attribute *net_class_attrs[] __ro_after_init = {

	&dev_attr_netdev_group.attr,

	&dev_attr_type.attr,
@@ -570,6 +609,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = { 
	&dev_attr_proto_down.attr,

	&dev_attr_carrier_up_count.attr,

	&dev_attr_carrier_down_count.attr,

	&dev_attr_threaded.attr,

	NULL,

};

ATTRIBUTE_GROUPS(net_class);