target/linux/generic/pending-5.4/690-net-add-support-for-threaded-NAPI-polling.patch

   1 From: Felix Fietkau <nbd@nbd.name>
   2 Date: Sun, 26 Jul 2020 14:03:21 +0200
   3 Subject: [PATCH] net: add support for threaded NAPI polling
   4
   5 For some drivers (especially 802.11 drivers), doing a lot of work in the NAPI
   6 poll function does not perform well. Since NAPI poll is bound to the CPU it
   7 was scheduled from, we can easily end up with a few very busy CPUs spending
   8 most of their time in softirq/ksoftirqd and some idle ones.
   9
  10 Introduce threaded NAPI for such drivers based on a workqueue. The API is the
  11 same except for using netif_threaded_napi_add instead of netif_napi_add.
  12
  13 In my tests with mt76 on MT7621 using threaded NAPI + a thread for tx scheduling
  14 improves LAN->WLAN bridging throughput by 10-50%. Throughput without threaded
  15 NAPI is wildly inconsistent, depending on the CPU that runs the tx scheduling
  16 thread.
  17
  18 With threaded NAPI it seems stable and consistent (and higher than the best
  19 results I got without it).
  20
  21 Based on a patch by Hillf Danton
  22
  23 Cc: Hillf Danton <hdanton@sina.com>
  24 Signed-off-by: Felix Fietkau <nbd@nbd.name>
  25 ---
  26
  27 --- a/include/linux/netdevice.h
  28 +++ b/include/linux/netdevice.h
  29 @@ -340,6 +340,7 @@ struct napi_struct {
  30         struct list_head        dev_list;
  31         struct hlist_node       napi_hash_node;
  32         unsigned int            napi_id;
  33 +       struct work_struct      work;
  34  };
  35
  36  enum {
  37 @@ -350,6 +351,7 @@ enum {
  38         NAPI_STATE_HASHED,      /* In NAPI hash (busy polling possible) */
  39         NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
  40         NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */
  41 +       NAPI_STATE_THREADED,    /* Use threaded NAPI */
  42  };
  43
  44  enum {
  45 @@ -360,6 +362,7 @@ enum {
  46         NAPIF_STATE_HASHED       = BIT(NAPI_STATE_HASHED),
  47         NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
  48         NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
  49 +       NAPIF_STATE_THREADED     = BIT(NAPI_STATE_THREADED),
  50  };
  51
  52  enum gro_result {
  53 @@ -2101,6 +2104,7 @@ struct net_device {
  54         struct lock_class_key   addr_list_lock_key;
  55         bool                    proto_down;
  56         unsigned                wol_enabled:1;
  57 +       unsigned                threaded:1;
  58  };
  59  #define to_net_dev(d) container_of(d, struct net_device, dev)
  60
  61 @@ -2281,6 +2285,26 @@ void netif_napi_add(struct net_device *d
  62                     int (*poll)(struct napi_struct *, int), int weight);
  63
  64  /**
  65 + *     netif_threaded_napi_add - initialize a NAPI context
  66 + *     @dev:  network device
  67 + *     @napi: NAPI context
  68 + *     @poll: polling function
  69 + *     @weight: default weight
  70 + *
  71 + * This variant of netif_napi_add() should be used from drivers using NAPI
  72 + * with CPU intensive poll functions.
  73 + * This will schedule polling from a high priority workqueue
  74 + */
  75 +static inline void netif_threaded_napi_add(struct net_device *dev,
  76 +                                          struct napi_struct *napi,
  77 +                                          int (*poll)(struct napi_struct *, int),
  78 +                                          int weight)
  79 +{
  80 +       set_bit(NAPI_STATE_THREADED, &napi->state);
  81 +       netif_napi_add(dev, napi, poll, weight);
  82 +}
  83 +
  84 +/**
  85   *     netif_tx_napi_add - initialize a NAPI context
  86   *     @dev:  network device
  87   *     @napi: NAPI context
  88 --- a/net/core/dev.c
  89 +++ b/net/core/dev.c
  90 @@ -156,6 +156,7 @@ static DEFINE_SPINLOCK(offload_lock);
  91  struct list_head ptype_base[PTYPE_HASH_SIZE] __read_mostly;
  92  struct list_head ptype_all __read_mostly;      /* Taps */
  93  static struct list_head offload_base __read_mostly;
  94 +static struct workqueue_struct *napi_workq __read_mostly;
  95
  96  static int netif_rx_internal(struct sk_buff *skb);
  97  static int call_netdevice_notifiers_info(unsigned long val,
  98 @@ -5937,6 +5938,11 @@ void __napi_schedule(struct napi_struct
  99  {
 100         unsigned long flags;
 101
 102 +       if (test_bit(NAPI_STATE_THREADED, &n->state)) {
 103 +               queue_work(napi_workq, &n->work);
 104 +               return;
 105 +       }
 106 +
 107         local_irq_save(flags);
 108         ____napi_schedule(this_cpu_ptr(&softnet_data), n);
 109         local_irq_restore(flags);
 110 @@ -5988,6 +5994,10 @@ EXPORT_SYMBOL(napi_schedule_prep);
 111   */
 112  void __napi_schedule_irqoff(struct napi_struct *n)
 113  {
 114 +       if (test_bit(NAPI_STATE_THREADED, &n->state)) {
 115 +               queue_work(napi_workq, &n->work);
 116 +               return;
 117 +       }
 118         if (!IS_ENABLED(CONFIG_PREEMPT_RT))
 119                 ____napi_schedule(this_cpu_ptr(&softnet_data), n);
 120         else
 121 @@ -6252,9 +6262,89 @@ static void init_gro_hash(struct napi_st
 122         napi->gro_bitmask = 0;
 123  }
 124
 125 +static int __napi_poll(struct napi_struct *n, bool *repoll)
 126 +{
 127 +       int work, weight;
 128 +
 129 +       weight = n->weight;
 130 +
 131 +       /* This NAPI_STATE_SCHED test is for avoiding a race
 132 +        * with netpoll's poll_napi().  Only the entity which
 133 +        * obtains the lock and sees NAPI_STATE_SCHED set will
 134 +        * actually make the ->poll() call.  Therefore we avoid
 135 +        * accidentally calling ->poll() when NAPI is not scheduled.
 136 +        */
 137 +       work = 0;
 138 +       if (test_bit(NAPI_STATE_SCHED, &n->state)) {
 139 +               work = n->poll(n, weight);
 140 +               trace_napi_poll(n, work, weight);
 141 +       }
 142 +
 143 +       WARN_ON_ONCE(work > weight);
 144 +
 145 +       if (likely(work < weight))
 146 +               return work;
 147 +
 148 +       /* Drivers must not modify the NAPI state if they
 149 +        * consume the entire weight.  In such cases this code
 150 +        * still "owns" the NAPI instance and therefore can
 151 +        * move the instance around on the list at-will.
 152 +        */
 153 +       if (unlikely(napi_disable_pending(n))) {
 154 +               napi_complete(n);
 155 +               return work;
 156 +       }
 157 +
 158 +       if (n->gro_bitmask) {
 159 +               /* flush too old packets
 160 +                * If HZ < 1000, flush all packets.
 161 +                */
 162 +               napi_gro_flush(n, HZ >= 1000);
 163 +       }
 164 +
 165 +       gro_normal_list(n);
 166 +
 167 +       *repoll = true;
 168 +
 169 +       return work;
 170 +}
 171 +
 172 +static void napi_workfn(struct work_struct *work)
 173 +{
 174 +       struct napi_struct *n = container_of(work, struct napi_struct, work);
 175 +       void *have;
 176 +
 177 +       for (;;) {
 178 +               bool repoll = false;
 179 +
 180 +               local_bh_disable();
 181 +
 182 +               have = netpoll_poll_lock(n);
 183 +               __napi_poll(n, &repoll);
 184 +               netpoll_poll_unlock(have);
 185 +
 186 +               local_bh_enable();
 187 +
 188 +               if (!repoll)
 189 +                       return;
 190 +
 191 +               if (!need_resched())
 192 +                       continue;
 193 +
 194 +               /*
 195 +                * have to pay for the latency of task switch even if
 196 +                * napi is scheduled
 197 +                */
 198 +               queue_work(napi_workq, work);
 199 +               return;
 200 +       }
 201 +}
 202 +
 203  void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
 204                     int (*poll)(struct napi_struct *, int), int weight)
 205  {
 206 +       if (dev->threaded)
 207 +               set_bit(NAPI_STATE_THREADED, &napi->state);
 208         INIT_LIST_HEAD(&napi->poll_list);
 209         hrtimer_init(&napi->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
 210         napi->timer.function = napi_watchdog;
 211 @@ -6271,6 +6361,7 @@ void netif_napi_add(struct net_device *d
 212  #ifdef CONFIG_NETPOLL
 213         napi->poll_owner = -1;
 214  #endif
 215 +       INIT_WORK(&napi->work, napi_workfn);
 216         set_bit(NAPI_STATE_SCHED, &napi->state);
 217         set_bit(NAPI_STATE_NPSVC, &napi->state);
 218         list_add_rcu(&napi->dev_list, &dev->napi_list);
 219 @@ -6311,6 +6402,7 @@ static void flush_gro_hash(struct napi_s
 220  void netif_napi_del(struct napi_struct *napi)
 221  {
 222         might_sleep();
 223 +       cancel_work_sync(&napi->work);
 224         if (napi_hash_del(napi))
 225                 synchronize_net();
 226         list_del_init(&napi->dev_list);
 227 @@ -6323,50 +6415,18 @@ EXPORT_SYMBOL(netif_napi_del);
 228
 229  static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 230  {
 231 +       bool do_repoll = false;
 232         void *have;
 233 -       int work, weight;
 234 +       int work;
 235
 236         list_del_init(&n->poll_list);
 237
 238         have = netpoll_poll_lock(n);
 239
 240 -       weight = n->weight;
 241 -
 242 -       /* This NAPI_STATE_SCHED test is for avoiding a race
 243 -        * with netpoll's poll_napi().  Only the entity which
 244 -        * obtains the lock and sees NAPI_STATE_SCHED set will
 245 -        * actually make the ->poll() call.  Therefore we avoid
 246 -        * accidentally calling ->poll() when NAPI is not scheduled.
 247 -        */
 248 -       work = 0;
 249 -       if (test_bit(NAPI_STATE_SCHED, &n->state)) {
 250 -               work = n->poll(n, weight);
 251 -               trace_napi_poll(n, work, weight);
 252 -       }
 253 -
 254 -       WARN_ON_ONCE(work > weight);
 255 +       work = __napi_poll(n, &do_repoll);
 256
 257 -       if (likely(work < weight))
 258 -               goto out_unlock;
 259 -
 260 -       /* Drivers must not modify the NAPI state if they
 261 -        * consume the entire weight.  In such cases this code
 262 -        * still "owns" the NAPI instance and therefore can
 263 -        * move the instance around on the list at-will.
 264 -        */
 265 -       if (unlikely(napi_disable_pending(n))) {
 266 -               napi_complete(n);
 267 +       if (!do_repoll)
 268                 goto out_unlock;
 269 -       }
 270 -
 271 -       if (n->gro_bitmask) {
 272 -               /* flush too old packets
 273 -                * If HZ < 1000, flush all packets.
 274 -                */
 275 -               napi_gro_flush(n, HZ >= 1000);
 276 -       }
 277 -
 278 -       gro_normal_list(n);
 279
 280         /* Some drivers may have called napi_schedule
 281          * prior to exhausting their budget.
 282 @@ -10346,6 +10406,10 @@ static int __init net_dev_init(void)
 283                 sd->backlog.weight = weight_p;
 284         }
 285
 286 +       napi_workq = alloc_workqueue("napi_workq", WQ_UNBOUND | WQ_HIGHPRI,
 287 +                                    WQ_UNBOUND_MAX_ACTIVE | WQ_SYSFS);
 288 +       BUG_ON(!napi_workq);
 289 +
 290         dev_boot_phase = 0;
 291
 292         /* The loopback device is special if any other network devices
 293 --- a/net/core/net-sysfs.c
 294 +++ b/net/core/net-sysfs.c
 295 @@ -442,6 +442,52 @@ static ssize_t proto_down_store(struct d
 296  }
 297  NETDEVICE_SHOW_RW(proto_down, fmt_dec);
 298
 299 +static int change_napi_threaded(struct net_device *dev, unsigned long val)
 300 +{
 301 +       struct napi_struct *napi;
 302 +
 303 +       if (list_empty(&dev->napi_list))
 304 +               return -EOPNOTSUPP;
 305 +
 306 +       list_for_each_entry(napi, &dev->napi_list, dev_list) {
 307 +               if (val)
 308 +                       set_bit(NAPI_STATE_THREADED, &napi->state);
 309 +               else
 310 +                       clear_bit(NAPI_STATE_THREADED, &napi->state);
 311 +       }
 312 +
 313 +       return 0;
 314 +}
 315 +
 316 +static ssize_t napi_threaded_store(struct device *dev,
 317 +                               struct device_attribute *attr,
 318 +                               const char *buf, size_t len)
 319 +{
 320 +       return netdev_store(dev, attr, buf, len, change_napi_threaded);
 321 +}
 322 +
 323 +static ssize_t napi_threaded_show(struct device *dev,
 324 +                                 struct device_attribute *attr,
 325 +                                 char *buf)
 326 +{
 327 +       struct net_device *netdev = to_net_dev(dev);
 328 +       struct napi_struct *napi;
 329 +       bool enabled = false;
 330 +
 331 +       if (!rtnl_trylock())
 332 +               return restart_syscall();
 333 +
 334 +       list_for_each_entry(napi, &netdev->napi_list, dev_list) {
 335 +               if (test_bit(NAPI_STATE_THREADED, &napi->state))
 336 +                       enabled = true;
 337 +       }
 338 +
 339 +       rtnl_unlock();
 340 +
 341 +       return sprintf(buf, fmt_dec, enabled);
 342 +}
 343 +static DEVICE_ATTR_RW(napi_threaded);
 344 +
 345  static ssize_t phys_port_id_show(struct device *dev,
 346                                  struct device_attribute *attr, char *buf)
 347  {
 348 @@ -532,6 +578,7 @@ static struct attribute *net_class_attrs
 349         &dev_attr_flags.attr,
 350         &dev_attr_tx_queue_len.attr,
 351         &dev_attr_gro_flush_timeout.attr,
 352 +       &dev_attr_napi_threaded.attr,
 353         &dev_attr_phys_port_id.attr,
 354         &dev_attr_phys_port_name.attr,
 355         &dev_attr_phys_switch_id.attr,