Re: [PATCH net-next v4] net/core: Introduce netdev_core_stats_inc() for trace

[Yajun Deng]

On 2023/9/19 17:10, Paolo Abeni wrote:
> On Mon, 2023-09-18 at 10:40 +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@xxxxxxxxx>
> > Suggested-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
> > ---
> > 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@xxxxxxxxx/
> > ---
> >   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 0896aaa91dd7..cddd4873b5b0 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -3980,32 +3980,19 @@ 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 ccff2b6ef958..f4cccdf05450 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -10475,7 +10475,8 @@ 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;
> >   
> > @@ -10488,7 +10489,28 @@ 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)
> > +{
> > +	/* 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)
> > +{
> > +	struct net_device_core_stats __percpu *p;
> > +
> > +	p = netdev_core_stats(dev);
> > +	if (p)
> > +		this_cpu_inc(*(unsigned long *)((void *)p + offset));
> The above is causing a lot of compile warning, as it's discarding the
> (required) __percpu annotation.
>
> You need to first access the per cpu pointer and then reach for the
> relevant offset.
Indeed, thanks.
> Cheers,
>
> Paolo