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From: Wei Wang <weiwan@google.com>
Date: Mon, 8 Feb 2021 11:34:09 -0800
Subject: [PATCH] net: implement threaded-able napi poll loop support
This patch allows running each napi poll loop inside its own
kernel thread.
The kthread is created during netif_napi_add() if dev->threaded
is set. And threaded mode is enabled in napi_enable(). We will
provide a way to set dev->threaded and enable threaded mode
without a device up/down in the following patch.
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.
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: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -347,6 +347,7 @@ struct napi_struct {
struct list_head dev_list;
struct hlist_node napi_hash_node;
unsigned int napi_id;
+ struct task_struct *thread;
};
enum {
@@ -357,6 +358,7 @@ 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 {
@@ -367,6 +369,7 @@ 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 {
@@ -497,20 +500,7 @@ static inline bool napi_complete(struct
*/
void napi_disable(struct napi_struct *n);
-/**
- * napi_enable - enable NAPI scheduling
- * @n: NAPI context
- *
- * Resume NAPI from being scheduled on this context.
- * Must be paired with napi_disable.
- */
-static inline void napi_enable(struct napi_struct *n)
-{
- BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
- smp_mb__before_atomic();
- clear_bit(NAPI_STATE_SCHED, &n->state);
- clear_bit(NAPI_STATE_NPSVC, &n->state);
-}
+void napi_enable(struct napi_struct *n);
/**
* napi_synchronize - wait until NAPI is not running
@@ -1835,6 +1825,8 @@ enum netdev_priv_flags {
*
* @wol_enabled: Wake-on-LAN is enabled
*
+ * @threaded: napi threaded mode is enabled
+ *
* @net_notifier_list: List of per-net netdev notifier block
* that follow this device when it is moved
* to another network namespace.
@@ -2152,6 +2144,7 @@ struct net_device {
struct lock_class_key *qdisc_running_key;
bool proto_down;
unsigned wol_enabled:1;
+ unsigned threaded:1;
struct list_head net_notifier_list;
--- 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>
@@ -1488,6 +1489,27 @@ void netdev_notify_peers(struct net_devi
}
EXPORT_SYMBOL(netdev_notify_peers);
+static int napi_threaded_poll(void *data);
+
+static int napi_kthread_create(struct napi_struct *n)
+{
+ int err = 0;
+
+ /* Create and wake up the kthread once to put it in
+ * TASK_INTERRUPTIBLE mode to avoid the blocked task
+ * warning and work with loadavg.
+ */
+ n->thread = kthread_run(napi_threaded_poll, n, "napi/%s-%d",
+ n->dev->name, n->napi_id);
+ if (IS_ERR(n->thread)) {
+ err = PTR_ERR(n->thread);
+ pr_err("kthread_run failed with err %d\n", err);
+ n->thread = NULL;
+ }
+
+ return err;
+}
+
static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
{
const struct net_device_ops *ops = dev->netdev_ops;
@@ -4242,6 +4264,21 @@ int gro_normal_batch __read_mostly = 8;
static inline void ____napi_schedule(struct softnet_data *sd,
struct napi_struct *napi)
{
+ struct task_struct *thread;
+
+ 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
+ * wake_up_process() when it's not NULL.
+ */
+ thread = READ_ONCE(napi->thread);
+ if (thread) {
+ wake_up_process(thread);
+ return;
+ }
+ }
+
list_add_tail(&napi->poll_list, &sd->poll_list);
__raise_softirq_irqoff(NET_RX_SOFTIRQ);
}
@@ -6693,6 +6730,12 @@ void netif_napi_add(struct net_device *d
set_bit(NAPI_STATE_NPSVC, &napi->state);
list_add_rcu(&napi->dev_list, &dev->napi_list);
napi_hash_add(napi);
+ /* Create kthread for this napi if dev->threaded is set.
+ * Clear dev->threaded if kthread creation failed so that
+ * threaded mode will not be enabled in napi_enable().
+ */
+ if (dev->threaded && napi_kthread_create(napi))
+ dev->threaded = 0;
}
EXPORT_SYMBOL(netif_napi_add);
@@ -6709,9 +6752,28 @@ void napi_disable(struct napi_struct *n)
hrtimer_cancel(&n->timer);
clear_bit(NAPI_STATE_DISABLE, &n->state);
+ clear_bit(NAPI_STATE_THREADED, &n->state);
}
EXPORT_SYMBOL(napi_disable);
+/**
+ * napi_enable - enable NAPI scheduling
+ * @n: NAPI context
+ *
+ * Resume NAPI from being scheduled on this context.
+ * Must be paired with napi_disable.
+ */
+void napi_enable(struct napi_struct *n)
+{
+ BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
+ smp_mb__before_atomic();
+ clear_bit(NAPI_STATE_SCHED, &n->state);
+ clear_bit(NAPI_STATE_NPSVC, &n->state);
+ if (n->dev->threaded && n->thread)
+ set_bit(NAPI_STATE_THREADED, &n->state);
+}
+EXPORT_SYMBOL(napi_enable);
+
static void flush_gro_hash(struct napi_struct *napi)
{
int i;
@@ -6737,6 +6799,11 @@ void __netif_napi_del(struct napi_struct
flush_gro_hash(napi);
napi->gro_bitmask = 0;
+
+ if (napi->thread) {
+ kthread_stop(napi->thread);
+ napi->thread = NULL;
+ }
}
EXPORT_SYMBOL(__netif_napi_del);
@@ -6818,6 +6885,51 @@ static int napi_poll(struct napi_struct
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)) {
+ WARN_ON(!list_empty(&napi->poll_list));
+ __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;
+ void *have;
+
+ while (!napi_thread_wait(napi)) {
+ for (;;) {
+ bool repoll = false;
+
+ local_bh_disable();
+
+ have = netpoll_poll_lock(napi);
+ __napi_poll(napi, &repoll);
+ netpoll_poll_unlock(have);
+
+ __kfree_skb_flush();
+ local_bh_enable();
+
+ if (!repoll)
+ break;
+
+ cond_resched();
+ }
+ }
+ return 0;
+}
+
static __latent_entropy void net_rx_action(struct softirq_action *h)
{
struct softnet_data *sd = this_cpu_ptr(&softnet_data);
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