netdev - Re: [PATCH net-next] net: tighten the definition of interface statistics

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Date:   Thu, 3 Sep 2020 16:40:54 -0600
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, jwi@...ux.ibm.com, f.fainelli@...il.com,
        andrew@...n.ch, mkubecek@...e.cz, edwin.peer@...adcom.com,
        michael.chan@...adcom.com, saeedm@...lanox.com,
        rmk+kernel@...linux.org.uk
Subject: Re: [PATCH net-next] net: tighten the definition of interface
 statistics

On 9/2/20 8:03 PM, Jakub Kicinski wrote:
> diff --git a/Documentation/networking/statistics.rst b/Documentation/networking/statistics.rst
> new file mode 100644
> index 000000000000..487b17c166e8
> --- /dev/null
> +++ b/Documentation/networking/statistics.rst

...

> +
> +sysfs
> +-----
> +
> +Each device directory in sysfs contains a `statistics` directory (e.g.
> +`/sys/class/net/lo/statistics/`) with files corresponding to
> +members of :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
> +
> +This simple interface is convenient especially in constrained/embedded
> +environments without access to tools. However, it's sightly inefficient

sightly seems like the wrong word. Did you mean 'highly inefficient'?

> +when reading multiple stats as it internally performs a full dump of
> +:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`
> +and reports only the stat corresponding to the accessed file.
> +
> +Sysfs files are documented in
> +`Documentation/ABI/testing/sysfs-class-net-statistics`.
> +
> +
> +netlink
> +-------
> +
> +`rtnetlink` (`NETLINK_ROUTE`) is the preferred method of accessing
> +:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` stats.
> +
> +Statistics are reported both in the responses to link information
> +requests (`RTM_GETLINK`) and statistic requests (`RTM_GETSTATS`,
> +when `IFLA_STATS_LINK_64` bit is set in the `.filter_mask` of the request).
> +
> +ethtool
> +-------
> +
> +Ethtool IOCTL interface allows drivers to report implementation
> +specific statistics.

an example here would be helpful. e.g., I use `ethool -S` primarily for
per queue stats which show more details than the other APIs which show
aggregated stats.



> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
> index 7fba4de511de..6ea0fb48739e 100644
> --- a/include/uapi/linux/if_link.h
> +++ b/include/uapi/linux/if_link.h
> @@ -40,26 +40,191 @@ struct rtnl_link_stats {
>  	__u32	rx_nohandler;		/* dropped, no handler found	*/
>  };
>  
> -/* The main device statistics structure */
> +/**
> + * struct rtnl_link_stats64 - The main device statistics structure.
> + *
> + * @rx_packets: Number of good packets received by the interface.
> + *   For hardware interfaces counts all good packets seen by the host,> + *   including packets which host had to drop at various stages of
processing
> + *   (even in the driver).
> + *
> + * @tx_packets: Number of packets successfully transmitted.
> + *   For hardware interfaces counts packets which host was able to successfully
> + *   hand over to the device, which does not necessarily mean that packets
> + *   had been successfully transmitted out of the device, only that device
> + *   acknowledged it copied them out of host memory.
> + *
> + * @rx_bytes: Number of good incoming bytes, corresponding to @rx_packets.

s/incoming/received/?

> + *
> + * @tx_bytes: Number of good incoming bytes, corresponding to @tx_packets.

s/incoming/transmitted/

Thanks for taking the time to work on this; I'm sure you spent a LOT of
hours going through all of the drivers and APIs.