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Subject: Re: [PATCH v9] virtio-net: support device stats
On Tue, Feb 15, 2022 at 03:47:43PM +0800, Xuan Zhuo wrote:
> This patch allows the driver to obtain some statistics from the device.
>
> In the back-end implementation, we can count a lot of such information,
> which can be used for debugging and judging the running status of the
> back-end. We hope to directly display it to the user through ethtool.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
> conformance.tex | 2 +
> content.tex | 135 ++++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 134 insertions(+), 3 deletions(-)
>
> diff --git a/conformance.tex b/conformance.tex
> index 42f8537..950924e 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -142,6 +142,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode}
> \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Offloads State Configuration / Setting Offloads State}
> \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) }
> +\item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Device stats}
> \end{itemize}
>
> \conformance{\subsection}{Block Driver Conformance}\label{sec:Conformance / Driver Conformance / Block Driver Conformance}
> @@ -401,6 +402,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
> \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Gratuitous Packet Sending}
> \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode}
> \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) / RSS processing}
> +\item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Device stats}
> \end{itemize}
>
> \conformance{\subsection}{Block Device Conformance}\label{sec:Conformance / Device Conformance / Block Device Conformance}
> diff --git a/content.tex b/content.tex
> index c6f116c..818275d 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -3092,6 +3092,9 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
> \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
> channel.
>
> +\item[VIRTIO_NET_F_CTRL_STATS(55)] Device can provide device-level statistics
> + to the driver through the control channel.
> +
> \item[VIRTIO_NET_F_HOST_USO (56)] Device can receive USO packets. Unlike UFO
> (fragmenting the packet) the USO splits large UDP packet
> to several segments when each of these smaller packets has UDP header.
> @@ -3137,6 +3140,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
> \item[VIRTIO_NET_F_GUEST_ANNOUNCE] Requires VIRTIO_NET_F_CTRL_VQ.
> \item[VIRTIO_NET_F_MQ] Requires VIRTIO_NET_F_CTRL_VQ.
> \item[VIRTIO_NET_F_CTRL_MAC_ADDR] Requires VIRTIO_NET_F_CTRL_VQ.
> +\item[VIRTIO_NET_F_CTRL_STATS] Requires VIRTIO_NET_F_CTRL_VQ.
> \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or VIRTIO_NET_F_HOST_TSO6.
> \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
> \end{description}
> @@ -4015,6 +4019,7 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
> u8 command;
> u8 command-specific-data[];
> u8 ack;
> + u8 command-specific-data-reply[];
> };
>
> /* ack values */
> @@ -4023,9 +4028,13 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
> \end{lstlisting}
>
> The \field{class}, \field{command} and command-specific-data are set by the
> -driver, and the device sets the \field{ack} byte. There is little it can
> -do except issue a diagnostic if \field{ack} is not
> -VIRTIO_NET_OK.
> +driver, and the device sets the \field{ack} byte and optionally
> +\field{command-specific-data-reply}. There is little the driver can
> +do except issue a diagnostic if \field{ack} is not VIRTIO_NET_OK.
> +
> +These commands VIRTIO_NET_CTRL_STATS_GET_DEV,
> +VIRTIO_NET_CTRL_STATS_GET_CTRL_VQ, and VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR contain
> +\field{command-specific-data-reply}.
>
> \paragraph{Packet Receive Filtering}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Packet Receive Filtering}
> \label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Setting Promiscuous Mode}%old label for latexdiff
> @@ -4471,6 +4480,126 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
> according to the native endian of the guest rather than
> (necessarily when not using the legacy interface) little-endian.
>
> +\paragraph{Device stats}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Device stats}
> +
> +If the VIRTIO_NET_F_CTRL_STATS feature is negotiated, the driver can
> +get device stats from the device in \field{command-specific-data-reply}.
> +
> +To get the stats, the following definitions are used:
> +\begin{lstlisting}
> +#define VIRTIO_NET_CTRL_STATS 6
> +#define VIRTIO_NET_CTRL_STATS_GET_DEV 0
> +#define VIRTIO_NET_CTRL_STATS_GET_CTRL_VQ 1
> +#define VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR 2
> +\end{lstlisting}
> +
> +The following layout structures are used:
> +
> +\field{command-specific-data}
> +\begin{lstlisting}
> +struct virtio_net_ctrl_stats_queue_pair {
> + le64 queue_pair_index;
> +}
> +\end{lstlisting}
> +
> +\field{command-specific-data-reply}
> +\begin{lstlisting}
> +struct virtio_net_ctrl_reply_stats_dev {
> + le64 mac_unicast_num; /* The number of unicast mac addresses. */
> + le64 mac_multicast_num; /* The number of multicast mac addresses. */
> + le64 vlan_num; /* The number of vlan. */
> +}
> +
> +struct virtio_net_ctrl_reply_stats_cvq {
> + le64 command_num; /* The number of commands, including the current command. */
> + le64 ok_num; /* The number of commands (including the current command) where the ack was VIRTIO_NET_OK. */
> +}
> +
> +struct virtio_net_ctrl_reply_stats_queue_pair {
> + /* rx stats */
> + le64 rx_packets; /* The number of packets received by device (not the packets passed to the guest), including the dropped packets by device. */
> + le64 rx_bytes; /* The number of bytes received by device (not the packets passed to the guest), including the dropped packets by device. */
> +
> + le64 rx_notification; /* The number of notifications from driver. */
> + le64 rx_interrupt; /* The number of interrupts generated by device. */
maybe device notifications/driver notifications?
> +
> + le64 rx_drop; /* The number of packets dropped by the rx queue. Contains all kinds of packet drop. */
> + le64 rx_drop_overruns; /* The number of packets dropped by the rx queue when no more descriptors were available. */
> +
> + le64 rx_csum_valid; /* The number of packets with VIRTIO_NET_HDR_F_DATA_VALID. */
> + le64 rx_csum_partial; /* The number of packets with VIRTIO_NET_HDR_F_NEEDS_CSUM. */
So why not rx_needs_csum?
> + le64 rx_csum_bad; /* The number of packets with abnormal csum. */
> + le64 rx_csum_none; /* The number of packets without hardware csum. */
these are only counted when rx checksum enabled and bad are then dropped
> +
> + le64 rx_gso_packets; /* The number of GSO packets written into the RX VQ buffers. */
still unclear what does this count exactly, and when.
> + le64 rx_gso_bytes; /* The number of bytes(excluding the virtio net header) of the GSO packets written into the RX VQ buffers. */
> + le64 rx_reset; /* The number of queue resets. */
> +
I'm not sure how we'll extend these, given there's no space between RX
and TX. Is there value in correlating rx and tx stats in a single
command, given they are on separate VQs?
> + /* tx stats */
> + le64 tx_packets; /* The number of packets sent by device (not the packets received from the guest), excluding the dropped packets by device. */
> + le64 tx_bytes; /* The number of bytes sent by device (not the packets received from the guest), excluding the dropped packets by device. */
> +
> + le64 tx_notification; /* The number of notifications from driver. */
> + le64 tx_interrupt; /* The number of interrupts generated by device. */
> +
> + le64 tx_drop; /* The number of packets dropped by the tx queue. Contains all kinds of packet drop. */
> + le64 tx_drop_malformed; /* The number of packets dropped when the descriptor is in an error state. */
Seems to imply some kind of error handling. A bit vague, I think we discussed this.
> +
> + le64 tx_csum_none; /* The number of packets that doesn't require hardware csum. */
that didn't require?
> + le64 tx_csum_partial; /* The number of packets that requires hardware csum. */
required?
> +
> + le64 tx_gso_packets; /* The number of GSO packets that the device received from the driver. */
> + le64 tx_gso_bytes; /* The number of bytes(excluding the virtio net header) of GSO packets that the device received from the driver. */
all of the above should be more explicit about which packet fields and which
values are meant.
> + le64 tx_reset; /* The number of queue resets. */
of the tx queue specifically? depends on the relevant flag?
> +}
> +\end{lstlisting}
> +
> +See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}
> +for more about \field{rx_reset} and \field{tx_reset}.
> +
> +All device stats are divided into three categories:
> +\begin{itemize}
> + \item the stats of the device.
> + \begin{description}
> + \item[command] VIRTIO_NET_CTRL_STATS_GET_DEV
> + \item[command-specific-data-reply] virtio_net_ctrl_reply_stats_dev
> + \end{description}
usefulness of this one is unclear.
> +
> + \item the stats of the controlq.
> + \begin{description}
> + \item[command] VIRTIO_NET_CTRL_STATS_GET_CTRL_VQ
> + \item[command-specific-data-reply] virtio_net_ctrl_reply_stats_cvq
> + \end{description}
> +
> + \item the stats of the queue pair.
of a specific queue pair
> This contains the stats of rx and tx.
> + \begin{description}
> + \item[command] VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR
> + \item[command-specific-data] virtio_net_ctrl_stats_queue_pair
> + \item[command-specific-data-reply] virtio_net_ctrl_reply_stats_queue_pair
> + \end{description}
> +\end{itemize}
> +
> +
> +\devicenormative{\subparagraph}{Device stats}{Device Types / Network Device / Device Operation / Control Virtqueue / Device stats}
> +
> +If VIRTIO_NET_F_CTRL_STATS has been negotiated, the device MUST support the
> +VIRTIO_NET_CTRL_STATS_GET_DEV, VIRTIO_NET_CTRL_STATS_GET_CTRL_VQ and
> +VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR commands.
why a single flag then?
> +
> +If \field{queue_pair_index} is out of range for a
> +VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR command, the device MUST set \field{ack} in
> +virtio_net_ctrl to VIRTIO_NET_ERR.
> +
> +If VIRTIO_NET_F_GUEST_CSUM is not successfully negotiated, all csum related
> +metrics MUST be 0.
why would tx counters be affected by this, as opposed to
VIRTIO_NET_F_CSUM? "csum related" means what?
> +
> +GSO packet refers to the packet of gso_type != VIRTIO_NET_HDR_GSO_NONE.
Let's write english not pseudo code by preference.
GSO packets refers to the number of packets with \field{gso_type} other than VIRTIO_NET_HDR_GSO_NONE
Also this kind of explanation belongs near where the term is used, not in a
separate paragraph.
> +All statistics on GSO MUST be based on the GSO packets.
The meaning of this is not very clear.
> +
> +\drivernormative{\subparagraph}{Device stats}{Device Types / Network Device / Device Operation / Control Virtqueue / Device stats}
> +
> +\field{command-specific-data} MUST be empty for VIRTIO_NET_CTRL_STATS_GET_DEV
> +and VIRTIO_NET_CTRL_STATS_GET_CTRL_VQ.
we need to give some thought to how we will extend these things.
how about we say that buffers can have extra space and it should
be ignored by device and driver respectively?
> \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device
> Types / Network Device / Legacy Interface: Framing Requirements}
> --
> 2.31.0
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