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Date: Mon, 8 Feb 2021 12:52:49 -0800
From: Alexander Duyck <alexander.duyck@...il.com>
To: Wei Wang <weiwan@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>,
Alexander Duyck <alexanderduyck@...com>,
Felix Fietkau <nbd@....name>
Subject: Re: [PATCH net-next v11 3/3] net: add sysfs attribute to control napi
threaded mode
On Mon, Feb 8, 2021 at 11:38 AM Wei Wang <weiwan@...gle.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@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> Co-developed-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Co-developed-by: Felix Fietkau <nbd@....name>
> Signed-off-by: Felix Fietkau <nbd@....name>
> Signed-off-by: Wei Wang <weiwan@...gle.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@...r.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@...r.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@...com>
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