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    SubjectRe: [PATCH net-next v5] net/core: Introduce netdev_core_stats_inc() for trace
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    On Tue, 2023-09-19 at 21:55 +0800, Yajun Deng wrote:
    > Although there is a kfree_skb_reason() helper function that can be used to
    > find the reason why this skb is dropped, but most callers didn't increase
    > one of rx_dropped, tx_dropped, rx_nohandler and rx_otherhost_dropped.
    >
    > For the users, people are more concerned about why the dropped in ip
    > is increasing.
    >
    > Introduce netdev_core_stats_inc() for trace. Also, move dev_core_stats()
    > and netdev_core_stats_alloc() to dev.c, as they are not called externally.
    >
    > Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
    > Suggested-by: Alexander Lobakin <aleksander.lobakin@intel.com>
    > ---
    > v5: Access the per cpu pointer before reach the relevant offset.
    > v4: Introduce netdev_core_stats_inc() instead of export dev_core_stats_*_inc()
    > v3: __cold should be added to the netdev_core_stats_alloc().
    > v2: use __cold instead of inline in dev_core_stats().
    > v1: https://lore.kernel.org/netdev/20230911082016.3694700-1-yajun.deng@linux.dev/
    > ---
    > include/linux/netdevice.h | 21 ++++-----------------
    > net/core/dev.c | 26 ++++++++++++++++++++++++--
    > 2 files changed, 28 insertions(+), 19 deletions(-)
    >
    > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
    > index db3d8429d50d..4c258d44c7d2 100644
    > --- a/include/linux/netdevice.h
    > +++ b/include/linux/netdevice.h
    > @@ -4001,32 +4001,19 @@ static __always_inline bool __is_skb_forwardable(const struct net_device *dev,
    > return false;
    > }
    >
    > -struct net_device_core_stats __percpu *netdev_core_stats_alloc(struct net_device *dev);
    > -
    > -static inline struct net_device_core_stats __percpu *dev_core_stats(struct net_device *dev)
    > -{
    > - /* This READ_ONCE() pairs with the write in netdev_core_stats_alloc() */
    > - struct net_device_core_stats __percpu *p = READ_ONCE(dev->core_stats);
    > -
    > - if (likely(p))
    > - return p;
    > -
    > - return netdev_core_stats_alloc(dev);
    > -}
    > +void netdev_core_stats_inc(struct net_device *dev, u32 offset);
    >
    > #define DEV_CORE_STATS_INC(FIELD) \
    > static inline void dev_core_stats_##FIELD##_inc(struct net_device *dev) \
    > { \
    > - struct net_device_core_stats __percpu *p; \
    > - \
    > - p = dev_core_stats(dev); \
    > - if (p) \
    > - this_cpu_inc(p->FIELD); \
    > + netdev_core_stats_inc(dev, \
    > + offsetof(struct net_device_core_stats, FIELD)); \
    > }
    > DEV_CORE_STATS_INC(rx_dropped)
    > DEV_CORE_STATS_INC(tx_dropped)
    > DEV_CORE_STATS_INC(rx_nohandler)
    > DEV_CORE_STATS_INC(rx_otherhost_dropped)
    > +#undef DEV_CORE_STATS_INC
    >
    > static __always_inline int ____dev_forward_skb(struct net_device *dev,
    > struct sk_buff *skb,
    > diff --git a/net/core/dev.c b/net/core/dev.c
    > index 606a366cc209..4bc0161bc0d6 100644
    > --- a/net/core/dev.c
    > +++ b/net/core/dev.c
    > @@ -10497,7 +10497,8 @@ void netdev_stats_to_stats64(struct rtnl_link_stats64 *stats64,
    > }
    > EXPORT_SYMBOL(netdev_stats_to_stats64);
    >
    > -struct net_device_core_stats __percpu *netdev_core_stats_alloc(struct net_device *dev)
    > +static __cold struct net_device_core_stats __percpu *netdev_core_stats_alloc(
    > + struct net_device *dev)
    > {
    > struct net_device_core_stats __percpu *p;
    >
    > @@ -10510,7 +10511,28 @@ struct net_device_core_stats __percpu *netdev_core_stats_alloc(struct net_device
    > /* This READ_ONCE() pairs with the cmpxchg() above */
    > return READ_ONCE(dev->core_stats);
    > }
    > -EXPORT_SYMBOL(netdev_core_stats_alloc);
    > +
    > +static inline struct net_device_core_stats __percpu *netdev_core_stats(
    > + struct net_device *dev)

    I'm sorry for the delayed feedback - conference and traveling in the
    way.

    It looks like the 'inline' keyword above is a left-over of a previous
    revision? The compiler should generate the same code even without it,
    right? If so, it should be better drop it.

    Cheers,

    Paolo

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