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Subject: Re: [PATCH v12] virtio-net: support inner header hash
å 2023/4/3 12:58, Heng Qi åé:
1. Currently, a received encapsulated packet has an outer and an inner header, but
the virtio device is unable to calculate the hash for the inner header. The same
flow can traverse through different tunnels, resulting in the encapsulated
packets being spread across multiple receive queues (refer to the figure below).
However, in certain scenarios, we may need to direct these encapsulated packets of
the same flow to a single receive queue. This facilitates the processing
of the flow by the same CPU to improve performance (warm caches, less locking, etc.).
client1 client2
| +-------+ |
+------->|tunnels|<--------+
+-------+
| |
v v
+-----------------+
| monitoring host |
+-----------------+
To achieve this, the device can calculate a suitable hash based on the inner headers
of this flow, for example using the Toeplitz combined with a symmetric hash key.
Some device allows sorting n tuples before calculating hash, do we need to consider them?
2. For legacy systems, they may lack entropy fields which modern protocols have in the outer header, resulting in multiple flows with the same outer header but different inner headers being directed to the same receive queue. This results in poor receive performance. To address this limitation, inner header hash can be used to enable the device to advertise the capability to calculate the hash for the inner packet, regaining better receive performance. Signed-off-by: Heng Qi<hengqi@linux.alibaba.com> Reviewed-by: Xuan Zhuo<xuanzhuo@linux.alibaba.com> --- v11->v12: 1. Add a command VIRTIO_NET_CTRL_MQ_TUNNEL_CONFIG. 2. Refine the commit log. @Michael S . Tsirkin 3. Add some tunnel types. v10->v11: 1. Revise commit log for clarity for readers. 2. Some modifications to avoid undefined terms. @Parav Pandit 3. Change VIRTIO_NET_F_HASH_TUNNEL dependency. @Parav Pandit 4. Add the normative statements. @Parav Pandit v9->v10: 1. Removed hash_report_tunnel related information. @Parav Pandit 2. Re-describe the limitations of QoS for tunneling. 3. Some clarification. v8->v9: 1. Merge hash_report_tunnel_types into hash_report. @Parav Pandit 2. Add tunnel security section. @Michael S . Tsirkin 3. Add VIRTIO_NET_F_HASH_REPORT_TUNNEL. 4. Fix some typos. 5. Add more tunnel types. @Michael S . Tsirkin v7->v8: 1. Add supported_hash_tunnel_types. @Jason Wang, @Parav Pandit 2. Change hash_report_tunnel to hash_report_tunnel_types. @Parav Pandit 3. Removed re-definition for inner packet hashing. @Parav Pandit 4. Fix some typos. @Michael S . Tsirkin 5. Clarify some sentences. @Michael S . Tsirkin v6->v7: 1. Modify the wording of some sentences for clarity. @Michael S. Tsirkin 2. Fix some syntax issues. @Michael S. Tsirkin v5->v6: 1. Fix some syntax and capitalization issues. @Michael S. Tsirkin 2. Use encapsulated/encaptulation uniformly. @Michael S. Tsirkin 3. Move the links to introduction section. @Michael S. Tsirkin 4. Clarify some sentences. @Michael S. Tsirkin v4->v5: 1. Clarify some paragraphs. @Cornelia Huck 2. Fix the u8 type. @Cornelia Huck v3->v4: 1. Rename VIRTIO_NET_F_HASH_GRE_VXLAN_GENEVE_INNER to VIRTIO_NET_F_HASH_TUNNEL. @Jason Wang 2. Make things clearer. @Jason Wang @Michael S. Tsirkin 3. Keep the possibility to use inner hash for automatic receive steering. @Jason Wang 4. Add the "Tunnel packet" paragraph to avoid repeating the GRE etc. many times. @Michael S. Tsirkin v2->v3: 1. Add a feature bit for GRE/VXLAN/GENEVE inner hash. @Jason Wang 2. Chang \field{hash_tunnel} to \field{hash_report_tunnel}. @Jason Wang, @Michael S. Tsirkin v1->v2: 1. Remove the patch for the bitmask fix. @Michael S. Tsirkin 2. Clarify some paragraphs. @Jason Wang 3. Add \field{hash_tunnel} and VIRTIO_NET_HASH_REPORT_GRE. @Yuri Benditovich device-types/net/description.tex | 143 ++++++++++++++++++++++++ device-types/net/device-conformance.tex | 1 + device-types/net/driver-conformance.tex | 1 + introduction.tex | 44 ++++++++ 4 files changed, 189 insertions(+) diff --git a/device-types/net/description.tex b/device-types/net/description.tex index 0500bb6..121585e 100644 --- a/device-types/net/description.tex +++ b/device-types/net/description.tex @@ -83,6 +83,9 @@ \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_HASH_TUNNEL(52)] Device supports inner header hash+ for tunnel-encapsulated packets. + \item[VIRTIO_NET_F_NOTF_COAL(53)] Device supports notifications coalescing.\item[VIRTIO_NET_F_GUEST_USO4 (54)] Driver can receive USOv4 packets.@@ -139,6 +142,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device \item[VIRTIO_NET_F_NOTF_COAL] 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. +\item[VIRTIO_NET_F_HASH_TUNNEL] Requires VIRTIO_NET_F_CTRL_VQ along with VIRTIO_NET_F_RSS and/or VIRTIO_NET_F_HASH_REPORT. \end{description}\subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}@@ -198,6 +202,7 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device u8 rss_max_key_size; le16 rss_max_indirection_table_length; le32 supported_hash_types; + le32 supported_tunnel_hash_types; }; \end{lstlisting} The following field, \field{rss_max_key_size} only exists if VIRTIO_NET_F_RSS or VIRTIO_NET_F_HASH_REPORT is set. @@ -212,6 +217,12 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device Field \field{supported_hash_types} contains the bitmask of supported hash types. See \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash types} for details of supported hash types.+Field \field{supported_tunnel_hash_types} only exists if the device+supports inner header hash, i.e. if VIRTIO_NET_F_HASH_TUNNEL is set. + +Filed \field{supported_tunnel_hash_types} contains the bitmask of supported tunnel hash types. +See \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled encapsulation hash types} for details of supported tunnel hash types. + \devicenormative{\subsubsection}{Device configuration layout}{Device Types / Network Device / Device configuration layout}The device MUST set \field{max_virtqueue_pairs} to between 1 and 0x8000 inclusive,@@ -848,6 +859,7 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network If the feature VIRTIO_NET_F_RSS was negotiated: \begin{itemize} \item The device uses \field{hash_types} of the virtio_net_rss_config structure as 'Enabled hash types' bitmask. +\item The device uses \field{hash_tunnel_types} of the virtio_net_hash_tunnel_config structure as 'Enabled hash tunnel types' bitmask if VIRTIO_NET_F_HASH_TUNNEL was negotiated. \item The device uses a key as defined in \field{hash_key_data} and \field{hash_key_length} of the virtio_net_rss_config structure (see \ref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Receive-side scaling (RSS) / Setting RSS parameters}). \end{itemize} @@ -855,6 +867,7 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network If the feature VIRTIO_NET_F_RSS was not negotiated: \begin{itemize} \item The device uses \field{hash_types} of the virtio_net_hash_config structure as 'Enabled hash types' bitmask. +\item The device uses \field{hash_tunnel_types} of the virtio_net_hash_tunnel_config structure as 'Enabled hash tunnel types' bitmask if VIRTIO_NET_F_HASH_TUNNEL was negotiated. \item The device uses a key as defined in \field{hash_key_data} and \field{hash_key_length} of the virtio_net_hash_config structure (see \ref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode / Hash calculation}). \end{itemize} @@ -870,6 +883,8 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network\subparagraph{Supported/enabled hash types}\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash types} +This paragraph relies on definitions from \hyperref[intro:IP]{[IP]}, +\hyperref[intro:UDP]{[UDP]} and \hyperref[intro:TCP]{[TCP]}. Hash types applicable for IPv4 packets: \begin{lstlisting} #define VIRTIO_NET_HASH_TYPE_IPv4 (1 << 0) @@ -980,6 +995,133 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network (see \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / IPv6 packets without extension header}). \end{itemize}+\paragraph{Inner Header Hash}+\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Inner Header Hash} + +If VIRTIO_NET_F_HASH_TUNNEL has been negotiated, the device supports inner header hash and +the driver can configure the inner header hash calculation for encapsulated packets \ref{sec:Device Types / Network Device / Device OperatiHn / Processing of Incoming Packets / Hash calculation for incoming packets / Tunnel/Encapsulated packet} +by issuing the command VIRTIO_NET_CTRL_MQ_TUNNEL_CONFIG from the class VIRTIO_NET_CTRL_MQ. +The command sets \field{hash_tunnel_types} in the structure virtio_net_hash_tunnel_config. + +struct virtio_net_hash_tunnel_config { + le32 hash_tunnel_types; +}; + +Filed \field{hash_tunnel_types} contains a bitmask of supported hash tunnel types as +defined in \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash tunnel types}. + +\subparagraph{Tunnel/Encapsulated packet} +\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Tunnel/Encapsulated packet} + +A tunnel packet is encapsulated from the original packet based on the tunneling +protocol (only a single level of encapsulation is currently supported). The +encapsulated packet contains an outer header and an inner header, and the device +calculates the hash over either the inner header or the outer header. + +If VIRTIO_NET_F_HASH_TUNNEL is negotiated and a received encapsulated packet's +outer header matches one of the supported \field{hash_tunnel_types}, the hash +of the inner header is calculated.
GRE allows X over Y, we'd better document what is supported in X and Y (I guess they are implied in the supported_hash_types?)
+
+Supported encapsulated packet types:
+\begin{itemize}
+\item \hyperref[intro:gre_rfc2784]{[GRE_rfc2784]}
+\item \hyperref[intro:gre_rfc2890]{[GRE_rfc2890]}
+\item \hyperref[intro:gre_rfc7676]{[GRE_rfc7676]}
+\item \hyperref[intro:gre_in_udp_rfc8086]{[GRE-in-UDP]}
+\item \hyperref[intro:vxlan]{[VXLAN]}
+\item \hyperref[intro:vxlan_gpe]{[VXLAN-GPE]}
+\item \hyperref[intro:geneve]{[GENEVE]}
+\item \hyperref[intro:ipip]{[IPIP]}
+\item \hyperref[intro:nvgre]{[NVGRE]}
+\item \hyperref[intro:sit]{[STT]}
+\end{itemize}
+
+If VIRTIO_NET_HASH_TUNNEL_TYPE_NONE is set or the encapsulation type is not included in
+\field{hash_tunnel_types}, the hash of the outer header is calculated for the received encapsulated packet.
+
+The hash is calculated for the received non-encapsulated packet as if VIRTIO_NET_F_HASH_TUNNEL was not negotiated.
+
+\subparagraph{Supported/enabled encapsulation hash types}
+\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled encapsulation hash types}
+
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_NONE (1 << 0)
+\end{lstlisting}
+
+Supported encapsulation hash types:
+Hash type applicable for inner payload of the \hyperref[intro:gre_rfc2784]{[GRE_rfc2784]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_2784 (1 << 1)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:gre_rfc2890]{[GRE_rfc2890]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_2890 (1 << 2)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:gre_rfc7676]{[GRE_rfc7676]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_7676 (1 << 3)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:gre_in_udp_rfc8086]{[GRE-in-UDP]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_GRE_UDP (1 << 4)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:vxlan]{[VXLAN]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_VXLAN (1 << 5)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:vxlan_gpe]{[VXLAN-GPE]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_VXLAN_GPE (1 << 6)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:geneve]{[GENEVE]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_GENEVE (1 << 7)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:ipip]{[IPIP]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_IPIP (1 << 8)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:nvgre]{[NVGRE]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_NVGRE (1 << 9)
+\end{lstlisting}
+Hash type applicable for inner payload of the \hyperref[intro:stt]{[STT]} packet:
+\begin{lstlisting}
+#define VIRTIO_NET_HASH_TUNNEL_TYPE_STT (1 << 10)
+\end{lstlisting}
+
+\subparagraph{Tunnel QoS limitation}
+When a specific receive queue is shared by multiple tunnels to receive encapsulated packets,
+there is no quality of service (QoS) for these packets.
This is up to the implementation, so I'm not sure it's worthwhile for mentioning things like this and the "limitation".
For example, when the packets of certain +tunnels are spread across multiple receive queues, these receive queues may have an unbalanced +amount of packets. This can cause a specific receive queue to become full, resulting in packet loss.
We have many places that can lead to packet dropping. For example, the automatic steering is best effort. I tend to avoid mentioning things like this.
+
+Possible mitigations:
+\begin{itemize}
+\item Use a tool with good forwarding performance to keep the receive queue from filling up.
+\item If the QoS is unavailable, the driver can set \field{hash_tunnel_types} to VIRTIO_NET_HASH_TUNNEL_TYPE_NONE
+ to disable inner header hash for encapsulated packets.
+\item Choose a hash key that can avoid queue collisions.
+\item Perform appropriate QoS before packets consume the receive buffers of the receive queues.
+\end{itemize}
+
+The limitations mentioned above exist with/without the inner header hash.
This conflicts with the tile "Tunnel QoS limitation" which readers may think it happens only for tunnel.
Thanks
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