221 lines
7.4 KiB
ReStructuredText
221 lines
7.4 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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====================
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Interface statistics
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====================
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Overview
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========
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This document is a guide to Linux network interface statistics.
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There are three main sources of interface statistics in Linux:
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- standard interface statistics based on
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`;
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- protocol-specific statistics; and
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- driver-defined statistics available via ethtool.
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Standard interface statistics
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-----------------------------
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There are multiple interfaces to reach the standard statistics.
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Most commonly used is the `ip` command from `iproute2`::
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$ ip -s -s link show dev ens4u1u1
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6: ens4u1u1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
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link/ether 48:2a:e3:4c:b1:d1 brd ff:ff:ff:ff:ff:ff
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RX: bytes packets errors dropped overrun mcast
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74327665117 69016965 0 0 0 0
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RX errors: length crc frame fifo missed
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0 0 0 0 0
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TX: bytes packets errors dropped carrier collsns
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21405556176 44608960 0 0 0 0
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TX errors: aborted fifo window heartbeat transns
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0 0 0 0 128
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altname enp58s0u1u1
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Note that `-s` has been specified twice to see all members of
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
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If `-s` is specified once the detailed errors won't be shown.
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`ip` supports JSON formatting via the `-j` option.
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Protocol-specific statistics
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----------------------------
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Protocol-specific statistics are exposed via relevant interfaces,
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the same interfaces as are used to configure them.
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ethtool
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~~~~~~~
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Ethtool exposes common low-level statistics.
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All the standard statistics are expected to be maintained
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by the device, not the driver (as opposed to driver-defined stats
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described in the next section which mix software and hardware stats).
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For devices which contain unmanaged
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switches (e.g. legacy SR-IOV or multi-host NICs) the events counted
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may not pertain exclusively to the packets destined to
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the local host interface. In other words the events may
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be counted at the network port (MAC/PHY blocks) without separation
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for different host side (PCIe) devices. Such ambiguity must not
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be present when internal switch is managed by Linux (so called
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switchdev mode for NICs).
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Standard ethtool statistics can be accessed via the interfaces used
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for configuration. For example ethtool interface used
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to configure pause frames can report corresponding hardware counters::
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$ ethtool --include-statistics -a eth0
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Pause parameters for eth0:
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Autonegotiate: on
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RX: on
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TX: on
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Statistics:
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tx_pause_frames: 1
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rx_pause_frames: 1
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General Ethernet statistics not associated with any particular
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functionality are exposed via ``ethtool -S $ifc`` by specifying
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the ``--groups`` parameter::
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$ ethtool -S eth0 --groups eth-phy eth-mac eth-ctrl rmon
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Stats for eth0:
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eth-phy-SymbolErrorDuringCarrier: 0
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eth-mac-FramesTransmittedOK: 1
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eth-mac-FrameTooLongErrors: 1
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eth-ctrl-MACControlFramesTransmitted: 1
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eth-ctrl-MACControlFramesReceived: 0
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eth-ctrl-UnsupportedOpcodesReceived: 1
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rmon-etherStatsUndersizePkts: 1
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rmon-etherStatsJabbers: 0
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rmon-rx-etherStatsPkts64Octets: 1
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rmon-rx-etherStatsPkts65to127Octets: 0
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rmon-rx-etherStatsPkts128to255Octets: 0
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rmon-tx-etherStatsPkts64Octets: 2
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rmon-tx-etherStatsPkts65to127Octets: 3
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rmon-tx-etherStatsPkts128to255Octets: 0
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Driver-defined statistics
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-------------------------
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Driver-defined ethtool statistics can be dumped using `ethtool -S $ifc`, e.g.::
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$ ethtool -S ens4u1u1
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NIC statistics:
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tx_single_collisions: 0
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tx_multi_collisions: 0
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uAPIs
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=====
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procfs
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------
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The historical `/proc/net/dev` text interface gives access to the list
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of interfaces as well as their statistics.
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Note that even though this interface is using
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`
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internally it combines some of the fields.
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sysfs
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-----
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Each device directory in sysfs contains a `statistics` directory (e.g.
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`/sys/class/net/lo/statistics/`) with files corresponding to
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members of :c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
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This simple interface is convenient especially in constrained/embedded
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environments without access to tools. However, it's inefficient when
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reading multiple stats as it internally performs a full dump of
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`
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and reports only the stat corresponding to the accessed file.
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Sysfs files are documented in
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`Documentation/ABI/testing/sysfs-class-net-statistics`.
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netlink
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-------
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`rtnetlink` (`NETLINK_ROUTE`) is the preferred method of accessing
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` stats.
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Statistics are reported both in the responses to link information
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requests (`RTM_GETLINK`) and statistic requests (`RTM_GETSTATS`,
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when `IFLA_STATS_LINK_64` bit is set in the `.filter_mask` of the request).
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ethtool
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-------
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Ethtool IOCTL interface allows drivers to report implementation
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specific statistics. Historically it has also been used to report
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statistics for which other APIs did not exist, like per-device-queue
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statistics, or standard-based statistics (e.g. RFC 2863).
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Statistics and their string identifiers are retrieved separately.
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Identifiers via `ETHTOOL_GSTRINGS` with `string_set` set to `ETH_SS_STATS`,
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and values via `ETHTOOL_GSTATS`. User space should use `ETHTOOL_GDRVINFO`
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to retrieve the number of statistics (`.n_stats`).
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ethtool-netlink
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---------------
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Ethtool netlink is a replacement for the older IOCTL interface.
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Protocol-related statistics can be requested in get commands by setting
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the `ETHTOOL_FLAG_STATS` flag in `ETHTOOL_A_HEADER_FLAGS`. Currently
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statistics are supported in the following commands:
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- `ETHTOOL_MSG_PAUSE_GET`
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- `ETHTOOL_MSG_FEC_GET`
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debugfs
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-------
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Some drivers expose extra statistics via `debugfs`.
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struct rtnl_link_stats64
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========================
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.. kernel-doc:: include/uapi/linux/if_link.h
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:identifiers: rtnl_link_stats64
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Notes for driver authors
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========================
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Drivers should report all statistics which have a matching member in
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>` exclusively
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via `.ndo_get_stats64`. Reporting such standard stats via ethtool
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or debugfs will not be accepted.
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Drivers must ensure best possible compliance with
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:c:type:`struct rtnl_link_stats64 <rtnl_link_stats64>`.
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Please note for example that detailed error statistics must be
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added into the general `rx_error` / `tx_error` counters.
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The `.ndo_get_stats64` callback can not sleep because of accesses
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via `/proc/net/dev`. If driver may sleep when retrieving the statistics
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from the device it should do so periodically asynchronously and only return
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a recent copy from `.ndo_get_stats64`. Ethtool interrupt coalescing interface
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allows setting the frequency of refreshing statistics, if needed.
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Retrieving ethtool statistics is a multi-syscall process, drivers are advised
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to keep the number of statistics constant to avoid race conditions with
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user space trying to read them.
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Statistics must persist across routine operations like bringing the interface
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down and up.
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Kernel-internal data structures
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-------------------------------
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The following structures are internal to the kernel, their members are
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translated to netlink attributes when dumped. Drivers must not overwrite
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the statistics they don't report with 0.
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- ethtool_pause_stats()
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- ethtool_fec_stats()
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