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diff --git a/Documentation/networking/statistics.rst b/Documentation/networking/statistics.rst new file mode 100644 index 000000000000..234abedc29b2 --- /dev/null +++ b/Documentation/networking/statistics.rst @@ -0,0 +1,178 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +Interface statistics +==================== + +Overview +======== + +This document is a guide to Linux network interface statistics. + +There are three main sources of interface statistics in Linux: + + - standard interface statistics based on + :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`; + - protocol-specific statistics; and + - driver-defined statistics available via ethtool. + +Standard interface statistics +----------------------------- + +There are multiple interfaces to reach the standard statistics. +Most commonly used is the `ip` command from `iproute2`:: + + $ ip -s -s link show dev ens4u1u1 + 6: ens4u1u1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000 + link/ether 48:2a:e3:4c:b1:d1 brd ff:ff:ff:ff:ff:ff + RX: bytes packets errors dropped overrun mcast + 74327665117 69016965 0 0 0 0 + RX errors: length crc frame fifo missed + 0 0 0 0 0 + TX: bytes packets errors dropped carrier collsns + 21405556176 44608960 0 0 0 0 + TX errors: aborted fifo window heartbeat transns + 0 0 0 0 128 + altname enp58s0u1u1 + +Note that `-s` has been specified twice to see all members of +:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`. +If `-s` is specified once the detailed errors won't be shown. + +`ip` supports JSON formatting via the `-j` option. + +Protocol-specific statistics +---------------------------- + +Some of the interfaces used for configuring devices are also able +to report related statistics. For example ethtool interface used +to configure pause frames can report corresponding hardware counters:: + + $ ethtool --include-statistics -a eth0 + Pause parameters for eth0: + Autonegotiate: on + RX: on + TX: on + Statistics: + tx_pause_frames: 1 + rx_pause_frames: 1 + +Driver-defined statistics +------------------------- + +Driver-defined ethtool statistics can be dumped using `ethtool -S $ifc`, e.g.:: + + $ ethtool -S ens4u1u1 + NIC statistics: + tx_single_collisions: 0 + tx_multi_collisions: 0 + +uAPIs +===== + +procfs +------ + +The historical `/proc/net/dev` text interface gives access to the list +of interfaces as well as their statistics. + +Note that even though this interface is using +:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` +internally it combines some of the fields. + +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 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. Historically it has also been used to report +statistics for which other APIs did not exist, like per-device-queue +statistics, or standard-based statistics (e.g. RFC 2863). + +Statistics and their string identifiers are retrieved separately. +Identifiers via `ETHTOOL_GSTRINGS` with `string_set` set to `ETH_SS_STATS`, +and values via `ETHTOOL_GSTATS`. User space should use `ETHTOOL_GDRVINFO` +to retrieve the number of statistics (`.n_stats`). + +ethtool-netlink +--------------- + +Ethtool netlink is a replacement for the older IOCTL interface. + +Protocol-related statistics can be requested in get commands by setting +the `ETHTOOL_FLAG_STATS` flag in `ETHTOOL_A_HEADER_FLAGS`. Currently +statistics are supported in the following commands: + + - `ETHTOOL_MSG_PAUSE_GET` + +debugfs +------- + +Some drivers expose extra statistics via `debugfs`. + +struct rtnl_link_stats64 +======================== + +.. kernel-doc:: include/uapi/linux/if_link.h + :identifiers: rtnl_link_stats64 + +Notes for driver authors +======================== + +Drivers should report all statistics which have a matching member in +:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` exclusively +via `.ndo_get_stats64`. Reporting such standard stats via ethtool +or debugfs will not be accepted. + +Drivers must ensure best possible compliance with +:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`. +Please note for example that detailed error statistics must be +added into the general `rx_error` / `tx_error` counters. + +The `.ndo_get_stats64` callback can not sleep because of accesses +via `/proc/net/dev`. If driver may sleep when retrieving the statistics +from the device it should do so periodically asynchronously and only return +a recent copy from `.ndo_get_stats64`. Ethtool interrupt coalescing interface +allows setting the frequency of refreshing statistics, if needed. + +Retrieving ethtool statistics is a multi-syscall process, drivers are advised +to keep the number of statistics constant to avoid race conditions with +user space trying to read them. + +Statistics must persist across routine operations like bringing the interface +down and up. + +Kernel-internal data structures +------------------------------- + +The following structures are internal to the kernel, their members are +translated to netlink attributes when dumped. Drivers must not overwrite +the statistics they don't report with 0. + +- ethtool_pause_stats() |