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Message-Id: <20200914172453.1833883-2-weiwan@google.com>
Date: Mon, 14 Sep 2020 10:24:48 -0700
From: Wei Wang <weiwan@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc: Jakub Kicinski <kuba@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>,
Felix Fietkau <nbd@....name>, Wei Wang <weiwan@...gle.com>
Subject: [RFC PATCH net-next 1/6] net: implement threaded-able napi poll loop support
From: Paolo Abeni <pabeni@...hat.com>
This patch allows running each napi poll loop inside its
own kernel thread.
The rx mode can be enabled per napi instance via the
newly addded napi_set_threaded() api; the requested kthread
will be created on demand and shut down on device stop.
Once that threaded mode is enabled and the kthread is
started, napi_schedule() will wake-up such thread instead
of scheduling the softirq.
The threaded poll loop behaves quite likely the net_rx_action,
but it does not have to manipulate local irqs and uses
an explicit scheduling point based on netdev_budget.
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
Signed-off-by: Wei Wang <weiwan@...gle.com>
---
include/linux/netdevice.h | 5 ++
net/core/dev.c | 113 ++++++++++++++++++++++++++++++++++++++
2 files changed, 118 insertions(+)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 157e0242e9ee..6797eb356e2e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -348,6 +348,7 @@ struct napi_struct {
struct list_head dev_list;
struct hlist_node napi_hash_node;
unsigned int napi_id;
+ struct task_struct *thread;
};
enum {
@@ -358,6 +359,7 @@ enum {
NAPI_STATE_LISTED, /* NAPI added to system lists */
NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */
+ NAPI_STATE_THREADED, /* The poll is performed inside its own thread*/
};
enum {
@@ -368,6 +370,7 @@ enum {
NAPIF_STATE_LISTED = BIT(NAPI_STATE_LISTED),
NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
+ NAPIF_STATE_THREADED = BIT(NAPI_STATE_THREADED),
};
enum gro_result {
@@ -489,6 +492,8 @@ static inline bool napi_complete(struct napi_struct *n)
return napi_complete_done(n, 0);
}
+int napi_set_threaded(struct napi_struct *n, bool threded);
+
/**
* napi_disable - prevent NAPI from scheduling
* @n: NAPI context
diff --git a/net/core/dev.c b/net/core/dev.c
index 03624192862a..0fe4c531b682 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -91,6 +91,7 @@
#include <linux/etherdevice.h>
#include <linux/ethtool.h>
#include <linux/skbuff.h>
+#include <linux/kthread.h>
#include <linux/bpf.h>
#include <linux/bpf_trace.h>
#include <net/net_namespace.h>
@@ -1486,9 +1487,19 @@ void netdev_notify_peers(struct net_device *dev)
}
EXPORT_SYMBOL(netdev_notify_peers);
+static int napi_threaded_poll(void *data);
+
+static void napi_thread_start(struct napi_struct *n)
+{
+ if (test_bit(NAPI_STATE_THREADED, &n->state) && !n->thread)
+ n->thread = kthread_create(napi_threaded_poll, n, "%s-%d",
+ n->dev->name, n->napi_id);
+}
+
static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
{
const struct net_device_ops *ops = dev->netdev_ops;
+ struct napi_struct *n;
int ret;
ASSERT_RTNL();
@@ -1520,6 +1531,9 @@ static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
if (!ret && ops->ndo_open)
ret = ops->ndo_open(dev);
+ list_for_each_entry(n, &dev->napi_list, dev_list)
+ napi_thread_start(n);
+
netpoll_poll_enable(dev);
if (ret)
@@ -1565,6 +1579,14 @@ int dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
}
EXPORT_SYMBOL(dev_open);
+static void napi_thread_stop(struct napi_struct *n)
+{
+ if (!n->thread)
+ return;
+ kthread_stop(n->thread);
+ n->thread = NULL;
+}
+
static void __dev_close_many(struct list_head *head)
{
struct net_device *dev;
@@ -1593,6 +1615,7 @@ static void __dev_close_many(struct list_head *head)
list_for_each_entry(dev, head, close_list) {
const struct net_device_ops *ops = dev->netdev_ops;
+ struct napi_struct *n;
/*
* Call the device specific close. This cannot fail.
@@ -1604,6 +1627,9 @@ static void __dev_close_many(struct list_head *head)
if (ops->ndo_stop)
ops->ndo_stop(dev);
+ list_for_each_entry(n, &dev->napi_list, dev_list)
+ napi_thread_stop(n);
+
dev->flags &= ~IFF_UP;
netpoll_poll_enable(dev);
}
@@ -4240,6 +4266,11 @@ int gro_normal_batch __read_mostly = 8;
static inline void ____napi_schedule(struct softnet_data *sd,
struct napi_struct *napi)
{
+ if (napi->thread) {
+ wake_up_process(napi->thread);
+ return;
+ }
+
list_add_tail(&napi->poll_list, &sd->poll_list);
__raise_softirq_irqoff(NET_RX_SOFTIRQ);
}
@@ -6590,6 +6621,30 @@ static void init_gro_hash(struct napi_struct *napi)
napi->gro_bitmask = 0;
}
+int napi_set_threaded(struct napi_struct *n, bool threaded)
+{
+ ASSERT_RTNL();
+
+ if (n->dev->flags & IFF_UP)
+ return -EBUSY;
+
+ if (threaded == !!test_bit(NAPI_STATE_THREADED, &n->state))
+ return 0;
+ if (threaded)
+ set_bit(NAPI_STATE_THREADED, &n->state);
+ else
+ clear_bit(NAPI_STATE_THREADED, &n->state);
+
+ /* if the device is initializing, nothing todo */
+ if (test_bit(__LINK_STATE_START, &n->dev->state))
+ return 0;
+
+ napi_thread_stop(n);
+ napi_thread_start(n);
+ return 0;
+}
+EXPORT_SYMBOL(napi_set_threaded);
+
void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int), int weight)
{
@@ -6730,6 +6785,64 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
return work;
}
+static int napi_thread_wait(struct napi_struct *napi)
+{
+ set_current_state(TASK_INTERRUPTIBLE);
+
+ while (!kthread_should_stop() && !napi_disable_pending(napi)) {
+ if (test_bit(NAPI_STATE_SCHED, &napi->state)) {
+ __set_current_state(TASK_RUNNING);
+ return 0;
+ }
+
+ schedule();
+ set_current_state(TASK_INTERRUPTIBLE);
+ }
+ __set_current_state(TASK_RUNNING);
+ return -1;
+}
+
+static int napi_threaded_poll(void *data)
+{
+ struct napi_struct *napi = data;
+
+ while (!napi_thread_wait(napi)) {
+ struct list_head dummy_repoll;
+ int budget = netdev_budget;
+ unsigned long time_limit;
+ bool again = true;
+
+ INIT_LIST_HEAD(&dummy_repoll);
+ local_bh_disable();
+ time_limit = jiffies + 2;
+ do {
+ /* ensure that the poll list is not empty */
+ if (list_empty(&dummy_repoll))
+ list_add(&napi->poll_list, &dummy_repoll);
+
+ budget -= napi_poll(napi, &dummy_repoll);
+ if (unlikely(budget <= 0 ||
+ time_after_eq(jiffies, time_limit))) {
+ cond_resched();
+
+ /* refresh the budget */
+ budget = netdev_budget;
+ __kfree_skb_flush();
+ time_limit = jiffies + 2;
+ }
+
+ if (napi_disable_pending(napi))
+ again = false;
+ else if (!test_bit(NAPI_STATE_SCHED, &napi->state))
+ again = false;
+ } while (again);
+
+ __kfree_skb_flush();
+ local_bh_enable();
+ }
+ return 0;
+}
+
static __latent_entropy void net_rx_action(struct softirq_action *h)
{
struct softnet_data *sd = this_cpu_ptr(&softnet_data);
--
2.28.0.618.gf4bc123cb7-goog
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