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Subject: Re: [virtio-dev] [PATCH v4] virtio-net: support device stats

• From: Jason Wang <jasowang@redhat.com>
• To: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
• Date: Thu, 9 Dec 2021 16:03:04 +0800

On Thu, Dec 9, 2021 at 2:20 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Mon, 6 Dec 2021 12:12:02 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > On Mon, Dec 6, 2021 at 11:07 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > On Tue, 28 Sep 2021 17:13:40 +0800, Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > Hi, everybody, is there anything else I need to do with this patch? When will
> > > this patch be merged into, so that I can carry out follow-up work.
> > >
> > > Thanks.
> > >
> > > > 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>
> > > > ---
> > > >
> > > > v4:
> > > > 1. remove dev_stats_num, {rx|tx}_stats_num
> > > > 2. Use two commands to get the stats of queue pair and dev respectively
> > > >
> > > > v3 changes:
> > > > 1. add dev_version
> > > > 2. use queue_pair_index replace rx_num, tx_num
> > > > 3. Explain the processing when the device and driver support different numbers
> > > > of stats
> > > >
> > > >
> > > >  content.tex | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> > > >  1 file changed, 77 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/content.tex b/content.tex
> > > > index 7cec1c3..ad8d781 100644
> > > > --- a/content.tex
> > > > +++ b/content.tex
> > > > @@ -2972,6 +2972,9 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
> > > >      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.
> > > > @@ -3017,6 +3020,7 @@ \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}
> > > > @@ -3895,6 +3899,7 @@ \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 */
> > > > @@ -3903,7 +3908,8 @@ \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
> > > > +driver, and the device sets the \field{ack} byte and optionally
> > > > +\field{command-specific-data-reply}. There is little it can
> > > >  do except issue a diagnostic if \field{ack} is not
> > > >  VIRTIO_NET_OK.
> > > >
> > > > @@ -4384,6 +4390,76 @@ \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device
> > > >  See \ref{sec:Basic
> > > >  Facilities of a Virtio Device / Virtqueues / Message Framing}.
> > > >
> > > > +\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 by \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_QUEUE_PAIR   1
> >
> > We need cvq stats as well.
>
> Yes, I will add cvq related in the next version.
>
> >
> > > > +\end{lstlisting}
> > > > +
> > > > +The following layout structure are used:
> > > > +
> > > > +\field{command-specific-data}
> > > > +\begin{lstlisting}
> > > > +struct virtio_net_ctrl_stats_queue_pair {
> > > > +    le64 queue_pair_index;
> > > > +}
> > > > +\end{lstlisting}
> > > > +
> > > > +\begin{lstlisting}
> > > > +struct virtio_net_ctrl_reply_stats_dev {
> > > > +    le64 dev_version;                // The number of device version.
> >
> > What's the use case for this field?
>
> Used to distinguish different versions of devices. For example, in a cloud
> environment, the device is provided by a cloud service provider. However, there
> may be multiple different versions. There will be some differences in functions
> and features between these different versions. Based on this Field users can
> know which version of the backend device they are currently using.
>
> Of course, for back-end devices using different series, this value may be
> meaningless.

I'd expect to use features instead of the version here. As we've
discussed, it looks to me it can introduce troubles for migration
compatibility.

>
>
> >
> > > > +    le64 dev_reset;                  // The number of device reset.
> > > > +}
> > > > +
> > > > +struct virtio_net_ctrl_reply_stats_queue_pair {
> > > > +    le64 queue_pair_index;
> > > > +    le64 rx_inter;                   // The number of interrupts sent by the rx queue.
> > > > +    le64 rx_drop;                    // The number of packets dropped by the rx queue. Contains all kinds of packet loss.
> > > > +    le64 rx_drop_overruns;   // The number of packets dropped by the rx queue when no more avail desc.
> > > > +    le64 rx_csum_bad;                // The number of packets with abnormal csum in the rx queue.
> > > > +    le64 rx_gso_packets;     // The number of gso packets received by rx.
> > > > +    le64 rx_gso_bytes;               // The number of gso bytes received by rx.
> >
> > It's kind of strange that we count gso packets without the the
> > packets/bytes regardless of gso or not.
>
> Since the driver already has statistics packets/bytes, and for the driver, this
> information can be easily counted. Do you think we need to add packets/bytes?

I think so, the counters at device level are even more important which
can be used for debugging.

>
> >
> > > > +    le64 rx_oversize_pkts;   // The number of oversized packets received by the rx queue.
> > > > +    le64 tx_inter;                   // The number of interrupts sent by the tx queue.
> > > > +    le64 tx_drop;                    // The number of packets dropped by the tx queue. Contains all kinds of packet loss.
> >
> > Is there any reason that can cause the packet to be dropped in tx by the device?
>
> For example, some scenarios where the flow rate is limited. And scenarios where
> the desc message sent by the driver is wrong.

Yes.

>
> >
> > > > +    le64 tx_csum;                    // The number of packets that completes csum by the device.
> > > > +    le64 tx_gso_packets;     // The number of gso packets transmitted.
> > > > +    le64 tx_gso_bytes;               // The number of gso bytes transmitted.
> > > > +}
> > > > +\end{lstlisting}
> > > > +
> > > > +All device stats is divided into two categories, one is the stats of the device,
> >
> > s/is/are/
> >
> > Btw, I wonder how easily we can extend the stats based on this.
>
>
>      "Probably not, looking at other NIC drivers the "keys" are pretty
>      stable. We can start from a large set anyhow."
>
> As we discussed earlier, expanding stats is a relatively rare thing. We will

Right, I forget that.

Thanks

>
> Thanks.
>
> >
> > Thanks
> >
> > > > +and the other is the stats of the queue pair. The queue pair stats contains the
> > > > +stats of rx and tx.
> > > > +
> > > > +The command VIRTIO_NET_CTRL_STATS_GET_DEV is used to obtain the stats of the device.
> > > > +The command VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR is used to obtain the stats of the queue pair.
> > > > +
> > > > +When the driver uses the command VIRTIO_NET_CTRL_STATS_GET_DEV,
> > > > +\field{command-specific-data} MUST be empty. The structure
> > > > +\field{virtio_net_ctrl_reply_stats_dev} MUST be used as
> > > > +
> > > > +When the driver uses the command VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR,
> > > > +\field{command-specific-data} MUST be \field{virtio_net_ctrl_stats_queue_pair}. At the same
> > > > +time, the structure \field{virtio_net_ctrl_reply_stats_queue_pair} MUST be used as
> > > > +\field{virtio_net_ctrl_stats_queue_pair.queue_pair_index} specify the queue pair
> > > > +index of the queue that the driver wants to get stats.
> > > > +
> > > > +The device MUST set \field{command-specific-data-reply} based on command.
> > > > +
> > > > +When the command is VIRTIO_NET_CTRL_STATS_GET_QUEUE_PAIR, the device MUST set
> > > > +\field{virtio_net_ctrl_reply_stats_queue_pair.queue_pair_index} equal to
> > > > +\field{virtio_net_ctrl_stats_queue_pair.queue_pair_index}
> > > > +
> > > >  \section{Block Device}\label{sec:Device Types / Block Device}
> > > >
> > > >  The virtio block device is a simple virtual block device (ie.
> > > > --
> > > > 2.31.0
> > > >
> > > >
> > > > ---------------------------------------------------------------------
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> > > >
> > >
> >
>



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