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From: Alexander Duyck <alexander.duyck@gmail.com>
To: Wei Wang <weiwan@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Netdev <netdev@vger.kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Paolo Abeni <pabeni@redhat.com>,
	Hannes Frederic Sowa <hannes@stressinduktion.org>,
	Alexander Duyck <alexanderduyck@fb.com>,
	Felix Fietkau <nbd@nbd.name>
Subject: Re: [PATCH net-next v11 3/3] net: add sysfs attribute to control napi threaded mode
Date: Mon, 8 Feb 2021 12:52:49 -0800	[thread overview]
Message-ID: <CAKgT0Uch5SzBZrqnyADQegFM5EAUzcidAuA_WTTZbcAmKn1X1w@mail.gmail.com> (raw)
In-Reply-To: <20210208193410.3859094-4-weiwan@google.com>

On Mon, Feb 8, 2021 at 11:38 AM Wei Wang <weiwan@google.com> wrote:
>
> This patch adds a new sysfs attribute to the network device class.
> Said attribute provides a per-device control to enable/disable the
> threaded mode for all the napi instances of the given network device,
> without the need for a device up/down.
> User sets it to 1 or 0 to enable or disable threaded mode.
> Note: when switching between threaded and the current softirq based mode
> for a napi instance, it will not immediately take effect if the napi is
> currently being polled. The mode switch will happen for the next time
> napi_schedule() is called.
>
> Co-developed-by: Paolo Abeni <pabeni@redhat.com>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> Co-developed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> Co-developed-by: Felix Fietkau <nbd@nbd.name>
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> Signed-off-by: Wei Wang <weiwan@google.com>
> ---
>  Documentation/ABI/testing/sysfs-class-net | 15 +++++++
>  include/linux/netdevice.h                 |  2 +
>  net/core/dev.c                            | 48 ++++++++++++++++++++++-
>  net/core/net-sysfs.c                      | 40 +++++++++++++++++++
>  4 files changed, 103 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
> index 1f2002df5ba2..1419103d11f9 100644
> --- a/Documentation/ABI/testing/sysfs-class-net
> +++ b/Documentation/ABI/testing/sysfs-class-net
> @@ -337,3 +337,18 @@ Contact:   netdev@vger.kernel.org
>  Description:
>                 32-bit unsigned integer counting the number of times the link has
>                 been down
> +
> +What:          /sys/class/net/<iface>/threaded
> +Date:          Jan 2021
> +KernelVersion: 5.12
> +Contact:       netdev@vger.kernel.org
> +Description:
> +               Boolean value to control the threaded mode per device. User could
> +               set this value to enable/disable threaded mode for all napi
> +               belonging to this device, without the need to do device up/down.
> +
> +               Possible values:
> +               == ==================================
> +               0  threaded mode disabled for this dev
> +               1  threaded mode enabled for this dev
> +               == ==================================
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 99fb4ec9573e..1340327f7abf 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -497,6 +497,8 @@ static inline bool napi_complete(struct napi_struct *n)
>         return napi_complete_done(n, 0);
>  }
>
> +int dev_set_threaded(struct net_device *dev, bool threaded);
> +
>  /**
>   *     napi_disable - prevent NAPI from scheduling
>   *     @n: NAPI context
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1e35f4f44f3b..7647278e46f0 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4291,8 +4291,9 @@ static inline void ____napi_schedule(struct softnet_data *sd,
>
>         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
> +                * napi_enable()/dev_set_threaded().
> +                * 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);
> @@ -6738,6 +6739,49 @@ static void init_gro_hash(struct napi_struct *napi)
>         napi->gro_bitmask = 0;
>  }
>
> +int dev_set_threaded(struct net_device *dev, bool threaded)
> +{
> +       struct napi_struct *napi;
> +       int err = 0;
> +
> +       if (dev->threaded == threaded)
> +               return 0;
> +
> +       if (threaded) {
> +               list_for_each_entry(napi, &dev->napi_list, dev_list) {
> +                       if (!napi->thread) {
> +                               err = napi_kthread_create(napi);
> +                               if (err) {
> +                                       threaded = false;
> +                                       break;
> +                               }
> +                       }
> +               }
> +       }
> +

So one idea on how to reduce the number of indents and braces would be
to look at pulling the threaded check into the loop. So something
like:

    list_for_each_entry(napi, &dev->napi_list, dev_list) {
        if (!threaded || napi->thread)
            continue;

        err = napi_kthread_create(napi);
        if (err)
            threaded = false;
    }

Anyway it is just a suggestion for improvement since it is
functionally the same as the code above but greatly reduces the
indentation. I am okay with the code as is as well, it just seemed
like a lot of braces on the end there.

> +       dev->threaded = threaded;
> +
> +       /* Make sure kthread is created before THREADED bit
> +        * is set.
> +        */
> +       smp_mb__before_atomic();
> +
> +       /* Setting/unsetting threaded mode on a napi might not immediately
> +        * take effect, if the current napi instance is actively being
> +        * polled. In this case, the switch between threaded mode and
> +        * softirq mode will happen in the next round of napi_schedule().
> +        * This should not cause hiccups/stalls to the live traffic.
> +        */
> +       list_for_each_entry(napi, &dev->napi_list, dev_list) {
> +               if (threaded)
> +                       set_bit(NAPI_STATE_THREADED, &napi->state);
> +               else
> +                       clear_bit(NAPI_STATE_THREADED, &napi->state);
> +       }
> +
> +       return err;
> +}
> +
>  void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
>                     int (*poll)(struct napi_struct *, int), int weight)
>  {
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index daf502c13d6d..e72d474c2623 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -538,6 +538,45 @@ static ssize_t phys_switch_id_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RO(phys_switch_id);
>
> +static ssize_t threaded_show(struct device *dev,
> +                            struct device_attribute *attr, char *buf)
> +{
> +       struct net_device *netdev = to_net_dev(dev);
> +       ssize_t ret = -EINVAL;
> +
> +       if (!rtnl_trylock())
> +               return restart_syscall();
> +
> +       if (dev_isalive(netdev))
> +               ret = sprintf(buf, fmt_dec, netdev->threaded);
> +
> +       rtnl_unlock();
> +       return ret;
> +}
> +
> +static int modify_napi_threaded(struct net_device *dev, unsigned long val)
> +{
> +       int ret;
> +
> +       if (list_empty(&dev->napi_list))
> +               return -EOPNOTSUPP;
> +
> +       if (val != 0 && val != 1)
> +               return -EOPNOTSUPP;
> +
> +       ret = dev_set_threaded(dev, val);
> +
> +       return ret;
> +}
> +
> +static ssize_t threaded_store(struct device *dev,
> +                             struct device_attribute *attr,
> +                             const char *buf, size_t len)
> +{
> +       return netdev_store(dev, attr, buf, len, modify_napi_threaded);
> +}
> +static DEVICE_ATTR_RW(threaded);
> +
>  static struct attribute *net_class_attrs[] __ro_after_init = {
>         &dev_attr_netdev_group.attr,
>         &dev_attr_type.attr,
> @@ -570,6 +609,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
>         &dev_attr_proto_down.attr,
>         &dev_attr_carrier_up_count.attr,
>         &dev_attr_carrier_down_count.attr,
> +       &dev_attr_threaded.attr,
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(net_class);

Other than the style nit I mentioned above the code looks good to me.

Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>

  reply	other threads:[~2021-02-08 20:55 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-08 19:34 [PATCH net-next v11 0/3] implement kthread based napi poll Wei Wang
2021-02-08 19:34 ` [PATCH net-next v11 1/3] net: extract napi poll functionality to __napi_poll() Wei Wang
2021-02-08 19:34 ` [PATCH net-next v11 2/3] net: implement threaded-able napi poll loop support Wei Wang
2021-02-08 19:34 ` [PATCH net-next v11 3/3] net: add sysfs attribute to control napi threaded mode Wei Wang
2021-02-08 20:52   ` Alexander Duyck [this message]
2021-02-09 23:50 ` [PATCH net-next v11 0/3] implement kthread based napi poll patchwork-bot+netdevbpf
2021-02-10 10:34 ` Paolo Abeni
2021-02-10 21:07   ` Wei Wang

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