Messages in this thread | | | Date | Fri, 29 Sep 2023 00:32:36 +0800 | Subject | Re: [PATCH v6] net/core: Introduce netdev_core_stats_inc() | From | Yajun Deng <> |
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On 2023/9/29 00:23, Eric Dumazet wrote: > 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. Okay, I'll test it. > >> 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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