linux-kernel - Re: [PATCH net-next v3] net/core: Export dev_core_stats_*

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Date:   Thu, 14 Sep 2023 17:22:00 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Yajun Deng <yajun.deng@...ux.dev>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <horms@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v3] net/core: Export dev_core_stats_*_inc()

From: Yajun Deng <yajun.deng@...ux.dev>
Date: Thu, 14 Sep 2023 10:37:18 +0800

> 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. So we can export dev_core_stats_rx_dropped_inc sets,
> which users would trace them know why rx_dropped is increasing.
> 
> Export dev_core_stats_{rx_dropped, tx_dropped, rx_nohandler,
> rx_otherhost_dropped}_inc for trace. Also, move dev_core_stats()
> and netdev_core_stats_alloc() to dev.c, as they are not called
> externally.

I'd like to hear some arguments against having them static inlines + one
external that I proposed earlier.

> 
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
> 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/

...as it's not at least mentioned here in the changelog.

[...]

> diff --git a/net/core/dev.c b/net/core/dev.c
> index ccff2b6ef958..98592e4c1df0 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10475,7 +10475,7 @@ 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)

This is way over 79/80 chars, break the line before "netdev_".

>  {
>  	struct net_device_core_stats __percpu *p;
>  
> @@ -10488,7 +10488,35 @@ 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 *dev_core_stats(struct net_device *dev)

Same for the line length.
Also notice that now some of the functions you touch have "dev_" prefix,
others have "netdev_", I'd probably take a look into unifying this.

(note for the maintainers that it would be probably better to leave
 explicit "inline" here, but no bloat-o-meter was provided by the
 author, so I can't say anything for sure)

> +{
> +	/* 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);
> +}

[...]

Thanks,
Olek