linux-kernel - Re: [PATCH net-next v4] net/core: Introduce netdev_core_stats

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Message-ID: <56c85b72-469c-bd46-dd5e-90ec58c6b49b@linux.dev>
Date:   Tue, 19 Sep 2023 21:42:23 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexander Lobakin <aleksander.lobakin@...el.com>
Subject: Re: [PATCH net-next v4] net/core: Introduce netdev_core_stats_inc()
 for trace


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@...ux.dev>
>> Suggested-by: Alexander Lobakin <aleksander.lobakin@...el.com>
>> ---
>> 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 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
>