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Date: Tue, 10 May 2016 16:11:53 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jiri Pirko <jiri@...lanox.com>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...mgrid.com>,
Alexander Duyck <aduyck@...antis.com>,
Tom Herbert <tom@...bertland.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>,
linux-kernel@...r.kernel.org
Subject: [RFC PATCH 1/2] net: implement threaded-able napi poll loop support
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>
---
include/linux/netdevice.h | 4 ++
net/core/dev.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 117 insertions(+)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 63580e6..0722ed5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -323,6 +323,7 @@ struct napi_struct {
struct list_head dev_list;
struct hlist_node napi_hash_node;
unsigned int napi_id;
+ struct task_struct *thread;
};
enum {
@@ -331,6 +332,7 @@ enum {
NAPI_STATE_NPSVC, /* Netpoll - don't dequeue from poll_list */
NAPI_STATE_HASHED, /* In NAPI hash (busy polling possible) */
NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
+ NAPI_STATE_THREADED, /* The poll is performed inside its own thread*/
};
enum gro_result {
@@ -475,6 +477,8 @@ static inline void napi_complete(struct napi_struct *n)
*/
void napi_hash_add(struct napi_struct *napi);
+int napi_set_threaded(struct napi_struct *n, bool threded);
+
/**
* napi_hash_del - remove a NAPI from global table
* @napi: NAPI context
diff --git a/net/core/dev.c b/net/core/dev.c
index c749033..0de286b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -94,6 +94,7 @@
#include <linux/ethtool.h>
#include <linux/notifier.h>
#include <linux/skbuff.h>
+#include <linux/kthread.h>
#include <net/net_namespace.h>
#include <net/sock.h>
#include <net/busy_poll.h>
@@ -1305,9 +1306,19 @@ void netdev_notify_peers(struct net_device *dev)
}
EXPORT_SYMBOL(netdev_notify_peers);
+static int napi_threaded_poll(void *data);
+
+static inline 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)
{
const struct net_device_ops *ops = dev->netdev_ops;
+ struct napi_struct *n;
int ret;
ASSERT_RTNL();
@@ -1334,6 +1345,9 @@ static int __dev_open(struct net_device *dev)
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)
@@ -1378,6 +1392,14 @@ int dev_open(struct net_device *dev)
}
EXPORT_SYMBOL(dev_open);
+static inline void napi_thread_stop(struct napi_struct *n)
+{
+ if (!n->thread)
+ return;
+ kthread_stop(n->thread);
+ n->thread = NULL;
+}
+
static int __dev_close_many(struct list_head *head)
{
struct net_device *dev;
@@ -1406,6 +1428,7 @@ static int __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.
@@ -1417,6 +1440,9 @@ static int __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);
}
@@ -3456,6 +3482,11 @@ int weight_p __read_mostly = 64; /* old backlog weight */
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);
}
@@ -5174,6 +5205,88 @@ out_unlock:
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_softirq();
+
+ /* 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;
+}
+
+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);
+
static void net_rx_action(struct softirq_action *h)
{
struct softnet_data *sd = this_cpu_ptr(&softnet_data);
--
1.8.3.1
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