Messages in this thread | | | From | Eric Dumazet <> | Date | Thu, 28 Sep 2023 18:23:11 +0200 | Subject | Re: [PATCH v6] net/core: Introduce netdev_core_stats_inc() |
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On Thu, Sep 28, 2023 at 6:16 PM Yajun Deng <yajun.deng@linux.dev> wrote: > > > On 2023/9/28 23:44, Eric Dumazet wrote: > > On Thu, Sep 28, 2023 at 5:40 PM Yajun Deng <yajun.deng@linux.dev> wrote: > >> > >> On 2023/9/28 22:18, Eric Dumazet wrote: > >>> 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 > >> Do you mean it needs to revert the commit 6510ea973d8d ("net: Use > >> this_cpu_inc() to increment > >> > >> net->core_stats") first? But it would allocate memory which breaks on > >> PREEMPT_RT. > > I think I provided an (untested) alternative. > > > > unsigned long __percpu *field = (__force unsigned long __percpu *) > > ((__force u8 *)p + offset); > > this_cpu_inc(field); > > unsigned long __percpu *field = (__force unsigned long __percpu *) > ((__force u8 *)p + offset); > this_cpu_inc(*(int *)field); > > This would compiler success. But I didn't test it. > This cold look complex.
Why exactly ? Not very different from the cast you already had.
> Shoud I base v3? Export dev_core_stats_*_inc() intead of introduce netdev_core_stats_inc(). > That would be easy.
Well, you tell me, but this does not look incremental to me.
I do not think we need 4 different (and maybe more to come if struct net_device_core_stats grows in the future) functions for some hardly used path.
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