virtio-net: support inner header hash

PATCH Superseded Heng Qi 3 participants 6 messages Jun 10, 2023 – Jun 12, 2023

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Heng Qi

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2023-06-10 04:11 UTC #0 lore raw

PATCH v16 1/1 virtio-net: support inner header hash

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 symmetric hash based on the inner headers of the same flow.

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.

Fixes https://github.com/oasis-tcs/virtio-spec/issues/173

Signed-off-by Heng Qi <[email protected]>

Reviewed-by Xuan Zhuo <[email protected]>

---
v15->v16:
1. Remove the hash_option. In order to delimit the inner header hash and RSS configuration, the ability to configure the outer src udp port hash is given to RSS. This is orthogonal to inner header hash, which will be done in the RSS capability extension topic (considered as an RSS extension together with the symmetric toeplitz hash algorithm, etc.). @Parav Pandit @Michael S . Tsirkin
2. Fix a 'field' typo. @Parav Pandit

v14->v15:
1. Add tunnel hash option suggested by @Michael S . Tsirkin
2. Adjust some descriptions.

v13->v14:
1. Move supported_hash_tunnel_types from config space into cvq command. @Parav Pandit
2. Rebase to master branch.
3. Some minor modifications.

v12->v13:
1. Add a GET command for hash_tunnel_types. @Parav Pandit
2. Add tunneling protocol explanation. @Jason Wang
3. Add comments on some usage scenarios for inner hash.

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        | 155 ++++++++++++++++++++++++
 device-types/net/device-conformance.tex |   1 +
 device-types/net/driver-conformance.tex |   1 +
 introduction.tex                        |  40 ++++++
 4 files changed, 197 insertions(+)

device-types/net/description.tex +155 -0

index 3030222..197d384 100644
@@ -88,6 +88,8 @@ \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(51)] Device supports inner header hash for tunnel-encapsulated packets.
+
 \item[VIRTIO_NET_F_VQ_NOTF_COAL(52)] Device supports virtqueue notification coalescing.
 
 \item[VIRTIO_NET_F_NOTF_COAL(53)] Device supports notifications coalescing.

@@ -147,6 +149,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device
 \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_VQ_NOTF_COAL] 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}

@@ -869,6 +872,7 @@ \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 virtnet_hash_tunnel_config_get structure as 'Enabled encapsulation hash 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}

@@ -876,6 +880,7 @@ \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 virtnet_hash_tunnel_config_get structure as 'Enabled encapsulation hash 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}

@@ -891,6 +896,7 @@ \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)

@@ -1001,6 +1007,155 @@ \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 driver can send commands VIRTIO_NET_CTRL_HASH_TUNNEL_SET
+and VIRTIO_NET_CTRL_HASH_TUNNEL_GET for the inner header hash configuration.
+
+struct virtnet_hash_tunnel_config_set {
+    le32 hash_tunnel_types;
+};
+
+struct virtnet_hash_tunnel_config_get {
+    le32 supported_hash_tunnel_types;
+    le32 hash_tunnel_types;
+};
+
+#define VIRTIO_NET_CTRL_HASH_TUNNEL 7
+ #define VIRTIO_NET_CTRL_HASH_TUNNEL_SET 0
+ #define VIRTIO_NET_CTRL_HASH_TUNNEL_GET 1
+
+Field \field{supported_hash_tunnel_types} provided by the device indicates that the device supports inner header hash for these encapsulation types.
+\field{supported_hash_tunnel_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}.
+
+Field \field{hash_tunnel_types} contains the bitmask of configured 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}.
+
+The class VIRTIO_NET_CTRL_HASH_TUNNEL has the following commands:
+\begin{itemize}
+\item VIRTIO_NET_CTRL_HASH_TUNNEL_SET: set \field{hash_tunnel_types} for the device using the virtnet_hash_tunnel_config_set structure, which is read-only for the driver.
+\item VIRTIO_NET_CTRL_HASH_TUNNEL_GET: get \field{hash_tunnel_types} and \field{supported_hash_tunnel_types} from the device using the virtnet_hash_tunnel_config_get
+      structure, which is write-only for the driver.
+\end{itemize}
+
+\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
+configured \field{hash_tunnel_types}, the hash of the inner header is calculated.
+
+Supported encapsulated packet types:
+\begin{itemize}
+\item \hyperref[intro:gre_rfc2784]{[GRE_rfc2784]}: the outer header is over IPv4 and the inner header is over IPv4. The outer header does not contain the transport protocol.
+\item \hyperref[intro:gre_rfc2890]{[GRE_rfc2890]}: the outer header is over IPv4 and the inner header is over IPv4. The outer header does not contain the transport protocol.
+\item \hyperref[intro:gre_rfc7676]{[GRE_rfc7676]}: the outer header is over IPv4/IPv6 and the inner header is over IPv4/IPv6. The outer header does not contain the transport protocol.
+\item \hyperref[intro:gre_in_udp_rfc8086]{[GRE-in-UDP]}: the outer header is over IPv4/IPv6 and the inner header is over IPv4/IPv6. The outer header uses UDP as the transport protocol.
+\item \hyperref[intro:vxlan]{[VXLAN]}: the outer header is over IPv4/IPv6 and the inner header is over IPv4/IPv6. The outer header uses UDP as the transport protocol.
+\item \hyperref[intro:vxlan_gpe]{[VXLAN-GPE]}: the outer header is over IPv4/IPv6 and the inner header is over IPv4/IPv6. The outer header uses UDP as the transport protocol.
+\item \hyperref[intro:geneve]{[GENEVE]}: the outer header is over IPv4/IPv6 and the inner header is over IPv4/IPv6. The outer header uses UDP as the transport protocol.
+\item \hyperref[intro:ipip]{[IPIP]}: the outer header is over IPv4 and the inner header is over IPv4. The outer header does not contain the transport protocol.
+\item \hyperref[intro:nvgre]{[NVGRE]}: the outer header is over IPv4/IPv6 and the inner header is over IPv4/IPv6. The outer header does not contain the transport protocol.
+\end{itemize}
+
+If VIRTIO_NET_HASH_TUNNEL_TYPE_NONE is set or the encapsulation type is not included in the configured \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}
+
+\subparagraph{Advice}
+Usage scenarios of inner header hash (but not limited to):
+\begin{itemize}
+\item Legacy tunneling protocols that lack entropy in the outer header use inner header hash to hash flows
+      with the same outer header but different inner headers to different queues for better-receiving performance.
+\item In scenarios where the same flow passing through different tunnels is expected to be received in the same queue,
+      warm caches, lessing locking, etc. are optimized to obtain receiving performance.
+\end{itemize}
+
+For scenarios with sufficient outer entropy or no inner header hash requirements, inner header hash may not be needed:
+A tunnel is often expected to isolate the external network from the internal one. By completely ignoring entropy
+in the outer header and replacing it with entropy from the inner header, for hash calculations, this expectation
+might be violated to a certain extent, depending on how the hash is used. When the hash use is limited to RSS queue
+selection, inner header hash may have quality of service (QoS) limitations.
+
+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 Perform appropriate QoS before packets consume the receive buffers of the receive queues.
+\end{itemize}
+
+\devicenormative{\subparagraph}{Inner Header Hash}{Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
+
+The device MUST calculate the hash on the outer header if the type of the received encapsulated packet does not match
+any value of the configured \field{hash_tunnel_types}.
+
+The device MUST respond to the VIRTIO_NET_CTRL_HASH_TUNNEL_SET command with VIRTIO_NET_ERR if the device receives
+an unsupported or unrecognized VIRTIO_NET_HASH_TUNNEL_TYPE_ flag.
+
+The device MUST provide the values of \field{supported_hash_tunnel_types} if it offers the VIRTIO_NET_F_HASH_TUNNEL feature.
+
+Upon reset, the device MUST initialize \field{hash_tunnel_type} to 0.
+
+\drivernormative{\subparagraph}{Inner Header Hash}{Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
+
+The driver MUST have negotiated the VIRTIO_NET_F_HASH_TUNNEL feature when issuing commands VIRTIO_NET_CTRL_HASH_TUNNEL_SET and VIRTIO_NET_CTRL_HASH_TUNNEL_GET.
+
+The driver MUST ignore the values received from the VIRTIO_NET_CTRL_HASH_TUNNEL_GET command if the device responds with VIRTIO_NET_ERR.
+
+The driver MUST NOT set any VIRTIO_NET_HASH_TUNNEL_TYPE_ flags which are not supported by the device.
+
 \paragraph{Hash reporting for incoming packets}
 \label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash reporting for incoming packets}

device-types/net/device-conformance.tex +1 -0

index 54f6783..f88f48b 100644
@@ -14,4 +14,5 @@
 \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 / Notifications Coalescing}
+\item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
 \end{itemize}

device-types/net/driver-conformance.tex +1 -0

index 97d0cc1..9d853d9 100644
@@ -14,4 +14,5 @@
 \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 / Notifications Coalescing}
+\item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Inner Header Hash}
 \end{itemize}

introduction.tex +40 -0

index b7155bf..3f34950 100644
@@ -102,6 +102,46 @@ \section{Normative References}\label{sec:Normative References}
     Standards for Efficient Cryptography Group(SECG), ``SEC1: Elliptic Cureve Cryptography'', Version 1.0, September 2000.
 	\newline\url{https://www.secg.org/sec1-v2.pdf}\\
 
+	\phantomsection\label{intro:gre_rfc2784}\textbf{[GRE_rfc2784]} &
+    Generic Routing Encapsulation. This protocol is only specified for IPv4 and used as either the payload or delivery protocol.
+	\newline\url{https://datatracker.ietf.org/doc/rfc2784/}\\
+	\phantomsection\label{intro:gre_rfc2890}\textbf{[GRE_rfc2890]} &
+    Key and Sequence Number Extensions to GRE \ref{intro:gre_rfc2784}. This protocol describes extensions by which two fields, Key and
+    Sequence Number, can be optionally carried in the GRE Header \ref{intro:gre_rfc2784}.
+	\newline\url{https://www.rfc-editor.org/rfc/rfc2890}\\
+	\phantomsection\label{intro:gre_rfc7676}\textbf{[GRE_rfc7676]} &
+    IPv6 Support for Generic Routing Encapsulation (GRE). This protocol is specified for IPv6 and used as either the payload or
+    delivery protocol. Note that this does not change the GRE header format or any behaviors specified by RFC 2784 or RFC 2890.
+	\newline\url{https://datatracker.ietf.org/doc/rfc7676/}\\
+	\phantomsection\label{intro:gre_in_udp_rfc8086}\textbf{[GRE-in-UDP]} &
+    GRE-in-UDP Encapsulation. This specifies a method of encapsulating network protocol packets within GRE and UDP headers.
+    This GRE-in-UDP encapsulation allows the UDP source port field to be used as an entropy field. This protocol is specified for IPv4 and IPv6,
+    and used as either the payload or delivery protocol.
+	\newline\url{https://www.rfc-editor.org/rfc/rfc8086}\\
+	\phantomsection\label{intro:vxlan}\textbf{[VXLAN]} &
+    Virtual eXtensible Local Area Network.
+	\newline\url{https://datatracker.ietf.org/doc/rfc7348/}\\
+	\phantomsection\label{intro:vxlan-gpe}\textbf{[VXLAN-GPE]} &
+    Generic Protocol Extension for VXLAN. This protocol describes extending Virtual eXtensible Local Area Network (VXLAN) via changes to the VXLAN header.
+	\newline\url{https://www.ietf.org/archive/id/draft-ietf-nvo3-vxlan-gpe-12.txt}\\
+	\phantomsection\label{intro:geneve}\textbf{[GENEVE]} &
+    Generic Network Virtualization Encapsulation.
+	\newline\url{https://datatracker.ietf.org/doc/rfc8926/}\\
+	\phantomsection\label{intro:ipip}\textbf{[IPIP]} &
+    IP Encapsulation within IP.
+	\newline\url{https://www.rfc-editor.org/rfc/rfc2003}\\
+	\phantomsection\label{intro:nvgre}\textbf{[NVGRE]} &
+    NVGRE: Network Virtualization Using Generic Routing Encapsulation
+	\newline\url{https://www.rfc-editor.org/rfc/rfc7637.html}\\
+	\phantomsection\label{intro:IP}\textbf{[IP]} &
+    INTERNET PROTOCOL
+	\newline\url{https://www.rfc-editor.org/rfc/rfc791}\\
+	\phantomsection\label{intro:UDP}\textbf{[UDP]} &
+    User Datagram Protocol
+	\newline\url{https://www.rfc-editor.org/rfc/rfc768}\\
+	\phantomsection\label{intro:TCP}\textbf{[TCP]} &
+    TRANSMISSION CONTROL PROTOCOL
+	\newline\url{https://www.rfc-editor.org/rfc/rfc793}\\
 \end{longtable}
 
 \section{Non-Normative References}

Signature · 18 lines

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Heng Qi

author

2023-06-10 04:28 UTC #1 lore raw

Quoted 33 lines · Heng Qi

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 symmetric hash based on the inner headers of the same flow.
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.
Fixes https://github.com/oasis-tcs/virtio-spec/issues/173
Signed-off-by Heng Qi <[email protected]>
Reviewed-by Xuan Zhuo <[email protected]>

Quoted 7 lines

---
v15->v16:
1. Remove the hash_option. In order to delimit the inner header hash and RSS configuration, the ability to configure the outer src udp port hash is given to RSS. This is orthogonal to inner header hash, which will be done in the RSS capability extension topic (considered as an RSS extension together with the symmetric toeplitz hash algorithm, etc.). @Parav Pandit @Michael S . Tsirkin

As we discussed in v15 about extending outer src udp port hash capability for RSS configuration, I rethink that it also needs a new feature bit. Because when a device that supports outer src udp port hash is migrated to a device that does not support that, the migration was successful but not as expected.

The RSS extension is orthogonal to the inner header hash.
So I plan to organize the symmetric toeplitz hash suggested by Michael earlier and the outer src udp port hash together as an RSS extension to initiate a patch(set).

Thanks!

Quoted 372 lines

2. Fix a 'field' typo. @Parav Pandit