From: Wei Wang 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 Signed-off-by: Paolo Abeni Co-developed-by: Hannes Frederic Sowa Signed-off-by: Hannes Frederic Sowa Co-developed-by: Jakub Kicinski Signed-off-by: Jakub Kicinski Signed-off-by: Wei Wang Reviewed-by: Alexander Duyck Signed-off-by: David S. Miller --- --- 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_HASHED, /* In NAPI hash (busy polling possible) */ 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_HASHED = BIT(NAPI_STATE_HASHED), 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 { @@ -511,20 +514,7 @@ bool napi_hash_del(struct napi_struct *n */ 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 @@ -1790,6 +1780,8 @@ enum netdev_ml_priv_type { * * @wol_enabled: Wake-on-LAN is enabled * + * @threaded: napi threaded mode is enabled + * * FIXME: cleanup struct net_device such that network protocol info * moves out. */ @@ -2082,6 +2074,7 @@ struct net_device { struct lock_class_key addr_list_lock_key; bool proto_down; unsigned wol_enabled:1; + unsigned threaded:1; }; #define to_net_dev(d) container_of(d, struct net_device, dev) --- a/net/core/dev.c +++ b/net/core/dev.c @@ -91,6 +91,7 @@ #include #include #include +#include #include #include #include @@ -1289,6 +1290,27 @@ 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; @@ -3889,6 +3911,21 @@ 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); } @@ -6280,6 +6317,12 @@ 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); @@ -6296,9 +6339,28 @@ 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; @@ -6323,6 +6385,11 @@ 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); @@ -6402,6 +6469,51 @@ 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);