Messages in this thread | | | From | Eric Dumazet <> | Date | Thu, 28 Sep 2023 16:18:11 +0200 | Subject | Re: [PATCH v6] net/core: Introduce netdev_core_stats_inc() |
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On Thu, Sep 28, 2023 at 12:04 PM Yajun Deng <yajun.deng@linux.dev> 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 the caller of the dropped > skb. Also, add __code to netdev_core_stats_alloc(), as it's called > unlinkly. > > Signed-off-by: Yajun Deng <yajun.deng@linux.dev> > Suggested-by: Alexander Lobakin <aleksander.lobakin@intel.com> > --- > v6: merge netdev_core_stats and netdev_core_stats_inc together > 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 | 17 +++++++++++++++-- > 2 files changed, 19 insertions(+), 19 deletions(-) > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > index 7e520c14eb8c..eb1fa04fbccc 100644 > --- a/include/linux/netdevice.h > +++ b/include/linux/netdevice.h > @@ -4002,32 +4002,19 @@ 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); \
Note that we were using this_cpu_inc() which implied : - IRQ safety, and - a barrier paired with :
net/core/dev.c:10548: storage->rx_dropped += READ_ONCE(core_stats->rx_dropped); net/core/dev.c:10549: storage->tx_dropped += READ_ONCE(core_stats->tx_dropped); net/core/dev.c:10550: storage->rx_nohandler += READ_ONCE(core_stats->rx_nohandler); net/core/dev.c:10551: storage->rx_otherhost_dropped += READ_ONCE(core_stats->rx_otherhost_dropped);
> + 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..88a32c392c1d 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 +10511,19 @@ 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); > + > +void netdev_core_stats_inc(struct net_device *dev, u32 offset) > +{ > + /* 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 (unlikely(!p)) > + p = netdev_core_stats_alloc(dev); > + > + if (p) > + (*(unsigned long *)((void *)this_cpu_ptr(p) + offset))++;
While here you are using a ++ operation that :
- is not irq safe - might cause store-tearing.
I would suggest a preliminary patch converting the "unsigned long" fields in struct net_device_core_stats to local_t
You might be able tweak this to
unsigned long __percpu *field = (unsigned long __percpu) ((u8 *)p + offset); this_cpu_inc(field);
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