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@@ -0,0 +1,339 @@
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+From: Felix Fietkau <[email protected]>
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+Date: Sun, 26 Jul 2020 14:03:21 +0200
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+Subject: [PATCH] net: add support for threaded NAPI polling
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+
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+For some drivers (especially 802.11 drivers), doing a lot of work in the NAPI
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+poll function does not perform well. Since NAPI poll is bound to the CPU it
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+was scheduled from, we can easily end up with a few very busy CPUs spending
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+most of their time in softirq/ksoftirqd and some idle ones.
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+
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+Introduce threaded NAPI for such drivers based on a workqueue. The API is the
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+same except for using netif_threaded_napi_add instead of netif_napi_add.
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+
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+In my tests with mt76 on MT7621 using threaded NAPI + a thread for tx scheduling
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+improves LAN->WLAN bridging throughput by 10-50%. Throughput without threaded
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+NAPI is wildly inconsistent, depending on the CPU that runs the tx scheduling
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+thread.
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+
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+With threaded NAPI it seems stable and consistent (and higher than the best
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+results I got without it).
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+
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+Based on a patch by Hillf Danton
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+
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+Cc: Hillf Danton <[email protected]>
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+Signed-off-by: Felix Fietkau <[email protected]>
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+---
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+
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+--- a/include/linux/netdevice.h
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++++ b/include/linux/netdevice.h
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+@@ -326,6 +326,7 @@ struct napi_struct {
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+ struct list_head dev_list;
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+ struct hlist_node napi_hash_node;
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+ unsigned int napi_id;
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++ struct work_struct work;
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+ };
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+
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+ enum {
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+@@ -336,6 +337,7 @@ enum {
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+ NAPI_STATE_HASHED, /* In NAPI hash (busy polling possible) */
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+ NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
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+ NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */
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++ NAPI_STATE_THREADED, /* Use threaded NAPI */
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+ };
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+
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+ enum {
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+@@ -346,6 +348,7 @@ enum {
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+ NAPIF_STATE_HASHED = BIT(NAPI_STATE_HASHED),
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+ NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
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+ NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
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++ NAPIF_STATE_THREADED = BIT(NAPI_STATE_THREADED),
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+ };
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+
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+ enum gro_result {
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+@@ -2093,6 +2096,26 @@ void netif_napi_add(struct net_device *d
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+ int (*poll)(struct napi_struct *, int), int weight);
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+
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+ /**
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++ * netif_threaded_napi_add - initialize a NAPI context
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++ * @dev: network device
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++ * @napi: NAPI context
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++ * @poll: polling function
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++ * @weight: default weight
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++ *
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++ * This variant of netif_napi_add() should be used from drivers using NAPI
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++ * with CPU intensive poll functions.
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++ * This will schedule polling from a high priority workqueue
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++ */
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++static inline void netif_threaded_napi_add(struct net_device *dev,
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++ struct napi_struct *napi,
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++ int (*poll)(struct napi_struct *, int),
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++ int weight)
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++{
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++ set_bit(NAPI_STATE_THREADED, &napi->state);
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++ netif_napi_add(dev, napi, poll, weight);
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++}
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++
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++/**
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+ * netif_tx_napi_add - initialize a NAPI context
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+ * @dev: network device
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+ * @napi: NAPI context
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+--- a/net/core/dev.c
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++++ b/net/core/dev.c
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+@@ -160,6 +160,7 @@ static DEFINE_SPINLOCK(offload_lock);
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+ struct list_head ptype_base[PTYPE_HASH_SIZE] __read_mostly;
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+ struct list_head ptype_all __read_mostly; /* Taps */
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+ static struct list_head offload_base __read_mostly;
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++static struct workqueue_struct *napi_workq __read_mostly;
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+
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+ static int netif_rx_internal(struct sk_buff *skb);
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+ static int call_netdevice_notifiers_info(unsigned long val,
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+@@ -5237,6 +5238,11 @@ void __napi_schedule(struct napi_struct
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+ {
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+ unsigned long flags;
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+
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++ if (test_bit(NAPI_STATE_THREADED, &n->state)) {
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++ queue_work(napi_workq, &n->work);
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++ return;
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++ }
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++
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+ local_irq_save(flags);
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+ ____napi_schedule(this_cpu_ptr(&softnet_data), n);
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+ local_irq_restore(flags);
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+@@ -5284,6 +5290,11 @@ EXPORT_SYMBOL(napi_schedule_prep);
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+ */
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+ void __napi_schedule_irqoff(struct napi_struct *n)
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+ {
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++ if (test_bit(NAPI_STATE_THREADED, &n->state)) {
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++ queue_work(napi_workq, &n->work);
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++ return;
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++ }
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++
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+ ____napi_schedule(this_cpu_ptr(&softnet_data), n);
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+ }
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+ EXPORT_SYMBOL(__napi_schedule_irqoff);
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+@@ -5521,6 +5532,82 @@ static enum hrtimer_restart napi_watchdo
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+ return HRTIMER_NORESTART;
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+ }
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+
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++static int __napi_poll(struct napi_struct *n, bool *repoll)
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++{
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++ int work, weight;
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++
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++ weight = n->weight;
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++
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++ /* This NAPI_STATE_SCHED test is for avoiding a race
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++ * with netpoll's poll_napi(). Only the entity which
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++ * obtains the lock and sees NAPI_STATE_SCHED set will
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++ * actually make the ->poll() call. Therefore we avoid
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++ * accidentally calling ->poll() when NAPI is not scheduled.
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++ */
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++ work = 0;
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++ if (test_bit(NAPI_STATE_SCHED, &n->state)) {
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++ work = n->poll(n, weight);
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++ trace_napi_poll(n, work, weight);
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++ }
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++
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++ WARN_ON_ONCE(work > weight);
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++
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++ if (likely(work < weight))
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++ return work;
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++
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++ /* Drivers must not modify the NAPI state if they
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++ * consume the entire weight. In such cases this code
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++ * still "owns" the NAPI instance and therefore can
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++ * move the instance around on the list at-will.
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++ */
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++ if (unlikely(napi_disable_pending(n))) {
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++ napi_complete(n);
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++ return work;
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++ }
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++
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++ if (n->gro_list) {
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++ /* flush too old packets
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++ * If HZ < 1000, flush all packets.
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++ */
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++ napi_gro_flush(n, HZ >= 1000);
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++ }
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++
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++ *repoll = true;
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++
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++ return work;
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++}
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++
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++static void napi_workfn(struct work_struct *work)
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++{
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++ struct napi_struct *n = container_of(work, struct napi_struct, work);
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++ void *have;
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++
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++ for (;;) {
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++ bool repoll = false;
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++
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++ local_bh_disable();
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++
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++ have = netpoll_poll_lock(n);
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++ __napi_poll(n, &repoll);
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++ netpoll_poll_unlock(have);
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++
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++ local_bh_enable();
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++
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++ if (!repoll)
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++ return;
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++
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++ if (!need_resched())
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++ continue;
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++
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++ /*
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++ * have to pay for the latency of task switch even if
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++ * napi is scheduled
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++ */
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++ queue_work(napi_workq, work);
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++ return;
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++ }
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++}
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++
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+ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
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+ int (*poll)(struct napi_struct *, int), int weight)
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+ {
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+@@ -5540,6 +5627,7 @@ void netif_napi_add(struct net_device *d
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+ #ifdef CONFIG_NETPOLL
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+ napi->poll_owner = -1;
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+ #endif
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++ INIT_WORK(&napi->work, napi_workfn);
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+ set_bit(NAPI_STATE_SCHED, &napi->state);
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+ napi_hash_add(napi);
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+ }
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+@@ -5565,6 +5653,7 @@ EXPORT_SYMBOL(napi_disable);
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+ void netif_napi_del(struct napi_struct *napi)
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+ {
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+ might_sleep();
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++ cancel_work_sync(&napi->work);
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+ if (napi_hash_del(napi))
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+ synchronize_net();
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+ list_del_init(&napi->dev_list);
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+@@ -5578,48 +5667,18 @@ EXPORT_SYMBOL(netif_napi_del);
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+
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+ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
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+ {
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++ bool do_repoll = false;
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+ void *have;
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+- int work, weight;
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++ int work;
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+
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+ list_del_init(&n->poll_list);
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+
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+ have = netpoll_poll_lock(n);
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+
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+- weight = n->weight;
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+-
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+- /* This NAPI_STATE_SCHED test is for avoiding a race
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+- * with netpoll's poll_napi(). Only the entity which
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+- * obtains the lock and sees NAPI_STATE_SCHED set will
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+- * actually make the ->poll() call. Therefore we avoid
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+- * accidentally calling ->poll() when NAPI is not scheduled.
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+- */
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+- work = 0;
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+- if (test_bit(NAPI_STATE_SCHED, &n->state)) {
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+- work = n->poll(n, weight);
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+- trace_napi_poll(n, work, weight);
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+- }
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+-
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+- WARN_ON_ONCE(work > weight);
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+-
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+- if (likely(work < weight))
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+- goto out_unlock;
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++ work = __napi_poll(n, &do_repoll);
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+
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+- /* Drivers must not modify the NAPI state if they
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+- * consume the entire weight. In such cases this code
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+- * still "owns" the NAPI instance and therefore can
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+- * move the instance around on the list at-will.
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+- */
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+- if (unlikely(napi_disable_pending(n))) {
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+- napi_complete(n);
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++ if (!do_repoll)
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+ goto out_unlock;
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+- }
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+-
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+- if (n->gro_list) {
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+- /* flush too old packets
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+- * If HZ < 1000, flush all packets.
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+- */
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+- napi_gro_flush(n, HZ >= 1000);
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+- }
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+
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+ /* Some drivers may have called napi_schedule
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+ * prior to exhausting their budget.
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+@@ -8855,6 +8914,10 @@ static int __init net_dev_init(void)
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+ sd->backlog.weight = weight_p;
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+ }
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+
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++ napi_workq = alloc_workqueue("napi_workq", WQ_UNBOUND | WQ_HIGHPRI,
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++ WQ_UNBOUND_MAX_ACTIVE | WQ_SYSFS);
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++ BUG_ON(!napi_workq);
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++
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+ dev_boot_phase = 0;
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+
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+ /* The loopback device is special if any other network devices
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+--- a/net/core/net-sysfs.c
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++++ b/net/core/net-sysfs.c
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+@@ -441,6 +441,52 @@ static ssize_t proto_down_store(struct d
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+ }
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+ NETDEVICE_SHOW_RW(proto_down, fmt_dec);
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+
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++static int change_napi_threaded(struct net_device *dev, unsigned long val)
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++{
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++ struct napi_struct *napi;
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++
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++ if (list_empty(&dev->napi_list))
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++ return -EOPNOTSUPP;
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++
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++ list_for_each_entry(napi, &dev->napi_list, dev_list) {
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++ if (val)
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++ set_bit(NAPI_STATE_THREADED, &napi->state);
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++ else
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++ clear_bit(NAPI_STATE_THREADED, &napi->state);
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++ }
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++
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++ return 0;
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++}
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++
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++static ssize_t napi_threaded_store(struct device *dev,
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++ struct device_attribute *attr,
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++ const char *buf, size_t len)
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++{
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++ return netdev_store(dev, attr, buf, len, change_napi_threaded);
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++}
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++
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++static ssize_t napi_threaded_show(struct device *dev,
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++ struct device_attribute *attr,
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++ char *buf)
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++{
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++ struct net_device *netdev = to_net_dev(dev);
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++ struct napi_struct *napi;
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++ bool enabled = false;
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++
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++ if (!rtnl_trylock())
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++ return restart_syscall();
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++
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++ list_for_each_entry(napi, &netdev->napi_list, dev_list) {
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++ if (test_bit(NAPI_STATE_THREADED, &napi->state))
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++ enabled = true;
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++ }
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++
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++ rtnl_unlock();
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++
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++ return sprintf(buf, fmt_dec, enabled);
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++}
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++static DEVICE_ATTR_RW(napi_threaded);
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++
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+ static ssize_t phys_port_id_show(struct device *dev,
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+ struct device_attribute *attr, char *buf)
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+ {
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+@@ -536,6 +582,7 @@ static struct attribute *net_class_attrs
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+ &dev_attr_flags.attr,
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+ &dev_attr_tx_queue_len.attr,
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+ &dev_attr_gro_flush_timeout.attr,
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++ &dev_attr_napi_threaded.attr,
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+ &dev_attr_phys_port_id.attr,
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+ &dev_attr_phys_port_name.attr,
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+ &dev_attr_phys_switch_id.attr,
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Felix Fietkau