target/linux/generic/backport-5.10/602-v5.12-net-add-sysfs-attribute-to-control-napi-threaded-mod.patch

   1 From: Wei Wang <weiwan@google.com>
   2 Date: Mon, 8 Feb 2021 11:34:10 -0800
   3 Subject: [PATCH] net: add sysfs attribute to control napi threaded mode
   4
   5 This patch adds a new sysfs attribute to the network device class.
   6 Said attribute provides a per-device control to enable/disable the
   7 threaded mode for all the napi instances of the given network device,
   8 without the need for a device up/down.
   9 User sets it to 1 or 0 to enable or disable threaded mode.
  10 Note: when switching between threaded and the current softirq based mode
  11 for a napi instance, it will not immediately take effect if the napi is
  12 currently being polled. The mode switch will happen for the next time
  13 napi_schedule() is called.
  14
  15 Co-developed-by: Paolo Abeni <pabeni@redhat.com>
  16 Signed-off-by: Paolo Abeni <pabeni@redhat.com>
  17 Co-developed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
  18 Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
  19 Co-developed-by: Felix Fietkau <nbd@nbd.name>
  20 Signed-off-by: Felix Fietkau <nbd@nbd.name>
  21 Signed-off-by: Wei Wang <weiwan@google.com>
  22 Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
  23 Signed-off-by: David S. Miller <davem@davemloft.net>
  24 ---
  25
  26 --- a/Documentation/ABI/testing/sysfs-class-net
  27 +++ b/Documentation/ABI/testing/sysfs-class-net
  28 @@ -337,3 +337,18 @@ Contact:   netdev@vger.kernel.org
  29  Description:
  30                 32-bit unsigned integer counting the number of times the link has
  31                 been down
  32 +
  33 +What:          /sys/class/net/<iface>/threaded
  34 +Date:          Jan 2021
  35 +KernelVersion: 5.12
  36 +Contact:       netdev@vger.kernel.org
  37 +Description:
  38 +               Boolean value to control the threaded mode per device. User could
  39 +               set this value to enable/disable threaded mode for all napi
  40 +               belonging to this device, without the need to do device up/down.
  41 +
  42 +               Possible values:
  43 +               == ==================================
  44 +               0  threaded mode disabled for this dev
  45 +               1  threaded mode enabled for this dev
  46 +               == ==================================
  47 --- a/include/linux/netdevice.h
  48 +++ b/include/linux/netdevice.h
  49 @@ -491,6 +491,8 @@ static inline bool napi_complete(struct
  50         return napi_complete_done(n, 0);
  51  }
  52
  53 +int dev_set_threaded(struct net_device *dev, bool threaded);
  54 +
  55  /**
  56   *     napi_disable - prevent NAPI from scheduling
  57   *     @n: NAPI context
  58 --- a/net/core/dev.c
  59 +++ b/net/core/dev.c
  60 @@ -4280,8 +4280,9 @@ static inline void ____napi_schedule(str
  61
  62         if (test_bit(NAPI_STATE_THREADED, &napi->state)) {
  63                 /* Paired with smp_mb__before_atomic() in
  64 -                * napi_enable(). Use READ_ONCE() to guarantee
  65 -                * a complete read on napi->thread. Only call
  66 +                * napi_enable()/dev_set_threaded().
  67 +                * Use READ_ONCE() to guarantee a complete
  68 +                * read on napi->thread. Only call
  69                  * wake_up_process() when it's not NULL.
  70                  */
  71                 thread = READ_ONCE(napi->thread);
  72 @@ -6716,6 +6717,49 @@ static void init_gro_hash(struct napi_st
  73         napi->gro_bitmask = 0;
  74  }
  75
  76 +int dev_set_threaded(struct net_device *dev, bool threaded)
  77 +{
  78 +       struct napi_struct *napi;
  79 +       int err = 0;
  80 +
  81 +       if (dev->threaded == threaded)
  82 +               return 0;
  83 +
  84 +       if (threaded) {
  85 +               list_for_each_entry(napi, &dev->napi_list, dev_list) {
  86 +                       if (!napi->thread) {
  87 +                               err = napi_kthread_create(napi);
  88 +                               if (err) {
  89 +                                       threaded = false;
  90 +                                       break;
  91 +                               }
  92 +                       }
  93 +               }
  94 +       }
  95 +
  96 +       dev->threaded = threaded;
  97 +
  98 +       /* Make sure kthread is created before THREADED bit
  99 +        * is set.
 100 +        */
 101 +       smp_mb__before_atomic();
 102 +
 103 +       /* Setting/unsetting threaded mode on a napi might not immediately
 104 +        * take effect, if the current napi instance is actively being
 105 +        * polled. In this case, the switch between threaded mode and
 106 +        * softirq mode will happen in the next round of napi_schedule().
 107 +        * This should not cause hiccups/stalls to the live traffic.
 108 +        */
 109 +       list_for_each_entry(napi, &dev->napi_list, dev_list) {
 110 +               if (threaded)
 111 +                       set_bit(NAPI_STATE_THREADED, &napi->state);
 112 +               else
 113 +                       clear_bit(NAPI_STATE_THREADED, &napi->state);
 114 +       }
 115 +
 116 +       return err;
 117 +}
 118 +
 119  void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
 120                     int (*poll)(struct napi_struct *, int), int weight)
 121  {
 122 --- a/net/core/net-sysfs.c
 123 +++ b/net/core/net-sysfs.c
 124 @@ -538,6 +538,45 @@ static ssize_t phys_switch_id_show(struc
 125  }
 126  static DEVICE_ATTR_RO(phys_switch_id);
 127
 128 +static ssize_t threaded_show(struct device *dev,
 129 +                            struct device_attribute *attr, char *buf)
 130 +{
 131 +       struct net_device *netdev = to_net_dev(dev);
 132 +       ssize_t ret = -EINVAL;
 133 +
 134 +       if (!rtnl_trylock())
 135 +               return restart_syscall();
 136 +
 137 +       if (dev_isalive(netdev))
 138 +               ret = sprintf(buf, fmt_dec, netdev->threaded);
 139 +
 140 +       rtnl_unlock();
 141 +       return ret;
 142 +}
 143 +
 144 +static int modify_napi_threaded(struct net_device *dev, unsigned long val)
 145 +{
 146 +       int ret;
 147 +
 148 +       if (list_empty(&dev->napi_list))
 149 +               return -EOPNOTSUPP;
 150 +
 151 +       if (val != 0 && val != 1)
 152 +               return -EOPNOTSUPP;
 153 +
 154 +       ret = dev_set_threaded(dev, val);
 155 +
 156 +       return ret;
 157 +}
 158 +
 159 +static ssize_t threaded_store(struct device *dev,
 160 +                             struct device_attribute *attr,
 161 +                             const char *buf, size_t len)
 162 +{
 163 +       return netdev_store(dev, attr, buf, len, modify_napi_threaded);
 164 +}
 165 +static DEVICE_ATTR_RW(threaded);
 166 +
 167  static struct attribute *net_class_attrs[] __ro_after_init = {
 168         &dev_attr_netdev_group.attr,
 169         &dev_attr_type.attr,
 170 @@ -570,6 +609,7 @@ static struct attribute *net_class_attrs
 171         &dev_attr_proto_down.attr,
 172         &dev_attr_carrier_up_count.attr,
 173         &dev_attr_carrier_down_count.attr,
 174 +       &dev_attr_threaded.attr,
 175         NULL,
 176  };
 177  ATTRIBUTE_GROUPS(net_class);