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vtnet.4: improve existing descriptions and add missing ones

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Improve several descriptions for loader tunables and add descriptions
of the statistics provided by read only sysctl-variables.

Reviewed by:		bcr
MFC after:		3 days
Sponsored by:		Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D51985
This commit is contained in:
Michael Tuexen 2025-08-21 17:11:06 +02:00
parent 267f8c1f4b
commit ac87d70563
1 changed files with 136 additions and 6 deletions
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142
share/man/man4/vtnet.4
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@ -22,7 +22,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd July 29, 2025
.Dd August 21, 2025
.Dt VTNET 4
.Os
.Sh NAME
@ -68,20 +68,29 @@ prompt before booting the kernel or stored in
.Bl -tag -width "xxxxxx"
.It Va hw.vtnet.csum_disable
.It Va hw.vtnet. Ns Ar X Ns Va .csum_disable
This tunable disables receive and send checksum offload.
This tunable disables receive and transmission checksum offloading for TCP and
UDP.
This also implies that TCP segmentation offloading and large receive offload
are disabled.
The default value is 0.
.It Va hw.vtnet.fixup_needs_csum
.It Va hw.vtnet. Ns Ar X Ns Va .fixup_needs_csum
This tunable enforces the calculation of a valid checksum for NEEDS_CSUM
packets.
This tunable enforces the calculation of a valid TCP or UDP checksum for
packets received with
.Dv VIRTIO_NET_HDR_F_NEEDS_CSUM
being set in the
.Va flags
field of the structure
.Vt struct virtio_net_hdr .
It also marks the checksum as being correct in the mbuf packet header.
The default value is 0.
.It Va hw.vtnet.tso_disable
.It Va hw.vtnet. Ns Ar X Ns Va .tso_disable
This tunable disables TSO.
This tunable disables TCP segmentation offloading.
The default value is 0.
.It Va hw.vtnet.lro_disable
.It Va hw.vtnet. Ns Ar X Ns Va .lro_disable
This tunable disables LRO.
This tunable disables large receive offload.
The default value is 0.
.It Va hw.vtnet.mq_disable
.It Va hw.vtnet. Ns Ar X Ns Va .mq_disable
@ -117,6 +126,127 @@ This tunable disables ALTQ support, allowing the use of multiqueue instead.
This option applies to all interfaces.
The default value is 0.
.El
.Sh TRANSMIT QUEUE STATISTICS
.Bl -tag -width "xxxxxx"
For each transmit queue of each interface the following read-only statistics
are provided:
.Bl -tag -width "xxxxxx"
.It Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .rescheduled
The number of times the transmit interrupt handler was rescheduled.
.It Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .tso
The number of times TCP segment offloading was performed.
.It Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .csum
The number of times transmission checksum offloading for UDP or TCP was
performed.
.It Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .omcasts
The number of multicast packets that were transmitted.
.It Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .obytes
The number of bytes that were transmitted (based on Ethernet frames).
.It Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .opackets
The number of packets that were transmitted (Ethernet frames).
.El
.Sh RECEIVE QUEUE STATISTICS
For each receive queue of each interface the following read-only statistics
are provided:
.Bl -tag -width "xxxxxx"
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .rescheduled
The number of times the receive interrupt handler was rescheduled.
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .host_lro
The number of times TCP large receive offload was performed.
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .csum_failed
Currently not used.
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .csum
The number of times receive checksum offloading for UDP or TCP was performed.
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .ierrors
The number of times an error occurred during input processing.
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .iqdrops
The number of times a packet was dropped during input processing.
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .ibytes
The number of bytes that were received (based on Ethernet frames).
.It Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .ipackets
The number of packets that were received (Ethernet frames).
.El
.Sh INTERFACE TRANSMIT STATISTICS
For each interface the following read-only transmit statistics are provided:
.Bl -tag -width "xxxxxx"
.It Va dev.vtnet. Ns Ar X Ns Va .tx_task_rescheduled
The sum of
.Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .rescheduled
over all transmit queues of the interface.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_tso_offloaded
The sum of
.Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .tso
over all transmit queues of the interface.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_csum_offloaded
The sum of
.Va dev.vtnet. Ns Ar X Ns Va .txq Ns Ar Y Ns Va .csum
over all transmit queues of the interface.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_defrag_failed
The number of times an attempt to defragment an mbuf chain failed during a
transmit operation.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_defragged
The number of times an mbuf chain was defragmented during a transmit operation.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_tso_without_csum
The number of times TCP segment offloading was attempted without transmission
checksum offloading.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_tso_not_tcp
The number of times TCP segment offloading was attempted for a non-TCP packet.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_csum_proto_mismatch
The number of times the IP protocol version of the transmission checksum
offloading request did not match the IP protocol version of the packet.
.It Va dev.vtnet. Ns Ar X Ns Va .tx_csum_unknown_ethtype
The number of times a transmission offload operation was requested for an
ethernet frame for which the EtherType was neither IPv4 nor IPv6
(considering simple VLAN tagging).
.El
.Sh INTERFACE RECEIVE STATISTICS
For each interface the following read-only receive statistics are provided:
.Bl -tag -width "xxxxxx"
.It Va dev.vtnet. Ns Ar X Ns Va .rx_task_rescheduled
The sum of
.Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .rescheduled
over all receive queues of the interface.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_csum_offloaded
The sum of
.Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .csum
over all receive queues of the interface.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_csum_failed
The sum of
.Va dev.vtnet. Ns Ar X Ns Va .rxq Ns Ar Y Ns Va .csum_failed
over all receive queues of the interface.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_csum_bad_proto
Currently unused.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_csum_bad_offset
Currently unused.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_csum_bad_ipproto
Currently unused.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_csum_bad_ethtype
The number of times fixing the checksum required by
.Va hw.vtnet.fixup_needs_csum
or
.Va hw.vtnet. Ns Ar X Ns Va .fixup_needs_csum
was attempted for a packet with an EtherType other than IPv4 or IPv6.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_mergeable_failed
The number of times receiving a mergable buffer failed.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_enq_replacement_failed
The number of times the enqueuing the replacement receive mbuf chain failed.
.It Va dev.vtnet. Ns Ar X Ns Va .rx_frame_too_large
The number of times the frame was loger than the mbuf chain during large
receive offload without mergeable buffers.
.It Va dev.vtnet. Ns Ar X Ns Va .mbuf_alloc_failed
The number of times an mbuf cluster allocation for the receive buffer failed.
.El
.Sh INTERFACE CONFIGURATION PARAMETER
For each interface the following read-only configuration parameters are
provided:
.Bl -tag -width "xxxxxx"
.It Va dev.vtnet. Ns Ar X Ns Va .act_vq_pairs
The number of active virtqueue pairs.
.It Va dev.vtnet. Ns Ar X Ns Va .req_vq_pairs
The number of requested virtqueue pairs.
.It Va dev.vtnet. Ns Ar X Ns Va .max_vq_pairs
The maximum number of supported virtqueue pairs.
.El
.Sh SEE ALSO
.Xr arp 4 ,
.Xr netintro 4 ,