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From: Wei Wang <weiwan@google.com>
Date: Mon, 8 Feb 2021 11:34:10 -0800
Subject: [PATCH] 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: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Co-developed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Co-developed-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Wei Wang <weiwan@google.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
--- a/Documentation/ABI/testing/sysfs-class-net
+++ b/Documentation/ABI/testing/sysfs-class-net
@@ -301,3 +301,18 @@ 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
+ == ==================================
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -498,6 +498,8 @@ static inline bool napi_complete(struct
*/
bool napi_hash_del(struct napi_struct *napi);
+int dev_set_threaded(struct net_device *dev, bool threaded);
+
/**
* napi_disable - prevent NAPI from scheduling
* @n: NAPI context
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3914,8 +3914,9 @@ static inline void ____napi_schedule(str
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);
@@ -6293,6 +6294,49 @@ static void init_gro_hash(struct napi_st
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)
{
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -557,6 +557,45 @@ static ssize_t phys_switch_id_show(struc
}
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,
@@ -587,6 +626,7 @@ static struct attribute *net_class_attrs
&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);
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