From: Sameeh Jubran <sjub...@redhat.com>

This commit introduces the RSS feature into virtio-net. It is introduced
as a sub mode for a general command which configures the steering mode.

Most modern high end network devices today support configurable hash functions,
this commit introduces RSS - Receive Side Scaling - [1] to virtio net device.

The RSS is a technology from Microsoft that boosts network device performance
by efficiently distributing the traffic among the CPUs in a multiprocessor
system.

This feature is supported in most of the modern network cards as well as most
modern OSes including Linux and Windows. It is worth mentioning that both DPDK
and Hyper-v support RSS too.

[1] 
https://docs.microsoft.com/en-us/windows-hardware/drivers/network/ndis-receive-side-scaling2

Signed-off-by: Sameeh Jubran <sjub...@redhat.com>
---
 content.tex | 114 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)

diff --git a/content.tex b/content.tex
index 3d538e8..8076147 100644
--- a/content.tex
+++ b/content.tex
@@ -4017,6 +4017,7 @@ The device MUST NOT queue packets on receive queues 
greater than
 \begin{lstlisting}
 // steering mode flags
 #define STEERING_MODE_AUTO          1
+#define STEERING_MODE_RSS           2
 
 struct virtio_net_steering_modes {
 le32 steering_modes;
@@ -4027,6 +4028,7 @@ le32 steering_mode;
 le32 command;
 
     union {
+    struct virtio_net_rss rss_conf;
     }
 };
 
@@ -4066,6 +4068,118 @@ If this feature has been negotiated, the virtio header 
has an additional
 
 This is the default steering mode, please refer to the "Automatic receive 
steering in multiqueue" section.
 
+\subparagraph{Receive Side Scaling}{Device Types / Network Device / Device 
Operation / Control Virtqueue / Steering mode / Receive Side Scaling}
+
+\begin{lstlisting}
+#define RSS_HASH_FUNCTION_NONE      1
+#define RSS_HASH_FUNCTION_TOEPLITZ  2
+#define RSS_HASH_FUNCTION_SYMMETRIC 3
+
+// Hash function fields
+#define RSS_HASH_FIELDS_IPV4          0x00000100
+#define RSS_HASH_FIELDS_TCP_IPV4      0x00000200
+#define RSS_HASH_FIELDS_IPV6          0x00000400
+#define RSS_HASH_FIELDS_IPV6_EX       0x00000800
+#define RSS_HASH_FIELDS_TCP_IPV6      0x00001000
+#define RSS_HASH_FIELDS_TCP_IPV6_EX   0x00002000
+
+struct virtio_net_rss_supported_hash{
+le32 hash_function;
+}
+
+struct virtio_net_rss {
+le32 hash_function;
+le32 hash_function_flags;
+le32 hash_key_length;
+le32 indirection_table_length;
+       struct {
+               le32 hash_key[hash_key_length];
+               le32 indirection_table[indirection_table_length];
+       }
+};
+
+#define VIRTIO_NET_SM_CTRL_RSS_GET_SUPPORTED_FUNCTIONS   0
+#define VIRTIO_NET_SM_CTRL_RSS_SET                       1
+\end{lstlisting}
+
+If the VIRTIO_NET_F_CTRL_STEERING_MODE is negotiated the driver can send 
control
+commands for the RSS configuration. For configuring RSS the 
virtio_net_steering_mode
+should be filled. The \field{steering_mode} field should be filled with the 
STEERING_MODE_RSS
+flag along with one of the VIRTIO_NET_SM_CTRL_RSS commands in the 
\field{command} field. The
+\field{rss_conf} field should be used.
+
+The class VIRTIO_NET_CTRL_RSS has two commands:
+
+\begin{enumerate}
+\item VIRTIO_NET_SM_CTRL_RSS_GET_SUPPORTED_FUNCTIONS returns the hash functions
+       supported by the device to the driver.
+\item VIRTIO_NET_SM_CTRL_RSS_SET applies the new RSS configuration. The 
command is
+       used by the driver for setting RSS hash function, hash key and
+       indirection table in the device.
+\end{enumerate}
+
+\devicenormative{\subparagraph}{Receive Side Scaling}{Device Types / Network 
Device / Device Operation / Control Virtqueue / Steering mode / Receive Side 
Scaling}
+
+The device MUST fill the virtio_net_rss_supported_hash structure with the hash
+functions it supports and return the structure to the driver. Zero or more
+flags of the RSS_HASH_FUNCTION flags MUST be used to fill the 
\field{hash_function}
+field.
+
+The device MUST drop all previous RSS configuration upon receiving
+VIRTIO_NET_SM_CTRL_RSS_SET command.
+
+The device MUST set the RSS configuration according to the settings provided as
+follows, once the configuration process is completed the device SHOULD apply
+the hash function to each of the incoming packets and distribute the packets
+through the virqueues using the calculated hash and the indirection table
+that were earlier provided by the driver.
+
+Setting RSS configuration
+\begin{enumerate}
+\item The driver fills all of the fields and passes them through the control
+       queue to the device.
+
+\item The device sets the RSS configuration as provided by the driver.
+
+\item If the device successfully applied the configuration, on each packet
+       received the device MUST calculate the hashing for the packet and
+       store it in the virtio-net header in the \field{hash} field and the
+       hash fields used in the calculation in rss_hash_type.
+\end{enumerate}
+
+In case of any unexpected values/ unsupported hash function the driver
+MUST return VIRTIO_NET_ERR in the \field{ack} field.
+
+\drivernormative{\subparagraph}{Receive Side Scaling}{Device Types / Network 
Device / Device Operation / Control Virtqueue / Steering mode / Receive Side 
Scaling}
+
+If the driver wants to set RSS hash it should fill the RSS structure fields
+as follows:
+
+\begin{itemize}
+\item The driver SHOULD choose the hash function that SHOULD be used and fill
+       it in the \field{hash_function} field along with the appropriate flags
+       in the \field{hash_function_flags} field. These flags indicate to the
+       device which packet fields MUST be used in the calculation process of
+       the hash.
+\item Once the hash function has been chosen a suitable hash key should be set
+       in the \field{hash_key} field, the length of the key should be stored
+       in the \field{hash_key_length} field.
+\item Lastly the driver should fill the indirection table array in the
+       \field{indirection_table} field while setting the array length in
+       \field{indirection_table_length}. This structure is used by the device
+       for determining in which RX virt queue the packet should be placed.
+\end{itemize}
+Once the configuration phase is over successfully, the packets SHOULD have the
+\field{hash} field with the hash value that was calculated by the device.
+
+Whenever the driver wants to discard the current RSS settings, it can send an
+VIRTIO_NET_SM_CTRL_RSS_SET command along with rss structure that has
+RSS_HASH_FUNCTION_NONE the \field{hash_function} field.
+
+The driver MUST check the \field{ack} field value provided by the device, in
+case the value is not VIRTIO_NET_OK then the driver MUST handle failure and
+retry another hash function or else give up.
+
 \subparagraph{Legacy Interface: Automatic receive steering in multiqueue 
mode}\label{sec:Device Types / Network Device / Device Operation / Control 
Virtqueue / Automatic receive steering in multiqueue mode / Legacy Interface: 
Automatic receive steering in multiqueue mode}
 When using the legacy interface, transitional devices and drivers
 MUST format \field{virtqueue_pairs}
-- 
2.13.6


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