Add RFS support to virtio network device.
Add a new feature flag VIRTIO_NET_F_RFS for this feature, a new
configuration field max_virtqueue_pairs to detect supported number of
virtqueues as well as a new command VIRTIO_NET_CTRL_RFS to program
packet steering for unidirectional protocols.
---
Changes from v4:
- address Jason's comments
- have configuration specify the number of VQ pairs and not pairs - 1
Changes from v3:
- rename multiqueue -> rfs this is what we support
- Be more explicit about what driver should do.
- Simplify layout making VQs functionality depend on feature.
- Remove unused commands, only leave in programming # of queues
Changes from v2:
Address Jason's comments on v2:
- Changed STEERING_HOST to STEERING_RX_FOLLOWS_TX:
this is both clearer and easier to support.
It does not look like we need a separate steering command
since host can just watch tx packets as they go.
- Moved RX and TX steering sections near each other.
- Add motivation for other changes in v2
Changes from Jason's rfc:
- reserved vq 3: this makes all rx vqs even and tx vqs odd, which
looks nicer to me.
- documented packet steering, added a generalized steering programming
command. Current modes are single queue and host driven multiqueue,
but I envision support for guest driven multiqueue in the future.
- make default vqs unused when in mq mode - this wastes some memory
but makes it more efficient to switch between modes as
we can avoid this causing packet reordering.
Rusty, could you please take a look and comment soon?
If this looks OK to everyone, we can proceed with finalizing the
implementation. Would be nice to try and put it in 3.8.
diff --git a/virtio-spec.lyx b/virtio-spec.lyx
index d2f0da9..53ddeec 100644
--- a/virtio-spec.lyx
+++ b/virtio-spec.lyx
@@ -59,6 +59,7 @@
\author -608949062 "Rusty Russell,,,"
\author -385801441 "Cornelia Huck" cornelia.h...@de.ibm.com
\author 1531152142 "Paolo Bonzini,,,"
+\author 1986246365 "Michael S. Tsirkin"
\end_header
\begin_body
@@ -4170,9 +4171,42 @@ ID 1
\end_layout
\begin_layout Description
-Virtqueues 0:receiveq.
- 1:transmitq.
- 2:controlq
+Virtqueues 0:receiveq
+\change_inserted 1986246365 1352742829
+0
+\change_unchanged
+.
+ 1:transmitq
+\change_inserted 1986246365 1352742832
+0
+\change_deleted 1986246365 1352742947
+.
+
+\change_inserted 1986246365 1352742952
+.
+ ....
+ 2N
+\begin_inset Foot
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1352743187
+N=0 if VIRTIO_NET_F_RFS is not negotiated, otherwise N is indicated by max_
+\emph on
+virtqueue_pairs control
+\emph default
+ field.
+
+\end_layout
+
+\end_inset
+
+: receivqN.
+ 2N+1: transmitqN.
+ 2N+
+\change_unchanged
+2:controlq
\begin_inset Foot
status open
@@ -4343,6 +4377,16 @@ VIRTIO_NET_F_CTRL_VLAN
\begin_layout Description
VIRTIO_NET_F_GUEST_ANNOUNCE(21) Guest can send gratuitous packets.
+\change_inserted 1986246365 1352742767
+
+\end_layout
+
+\begin_layout Description
+
+\change_inserted 1986246365 1352742808
+VIRTIO_NET_F_RFS(22) Device supports Receive Flow Steering.
+\change_unchanged
+
\end_layout
\end_deeper
@@ -4355,11 +4399,45 @@ configuration
\begin_inset space ~
\end_inset
-layout Two configuration fields are currently defined.
+layout
+\change_deleted 1986246365 1352743300
+Two
+\change_inserted 1986246365 1352743301
+Four
+\change_unchanged
+ configuration fields are currently defined.
The mac address field always exists (though is only valid if VIRTIO_NET_F_MAC
is set), and the status field only exists if VIRTIO_NET_F_STATUS is set.
Two read-only bits are currently defined for the status field:
VIRTIO_NET_S_LIN
K_UP and VIRTIO_NET_S_ANNOUNCE.
+
+\change_inserted 1986246365 1353595219
+ The following read-only field,
+\emph on
+max_virtqueue_pairs
+\emph default
+ only exists if VIRTIO_NET_F_RFS is set.
+ This field specifies the maximum number of each of transmit and receive
+ virtqueues (receiveq0..receiveq
+\emph on
+N
+\emph default
+ and transmitq0..transmitq
+\emph on
+N
+\emph default
+ respectively;
+\emph on
+N
+\emph default
+=
+\emph on
+max_virtqueue_pairs - 1
+\emph default
+) that can be configured once VIRTIO_NET_F_RFS is negotiated.
+Legal values for this field are 1 to 8000h.
+
+\change_unchanged
\begin_inset listings
inline false
@@ -4410,7 +4488,24 @@ Device Initialization
\begin_layout Enumerate
The initialization routine should identify the receive and transmission
- virtqueues.
+ virtqueues
+\change_inserted 1986246365 1352744077
+, up to N+1 of each kind
+\change_unchanged
+.
+
+\change_inserted 1986246365 1352743942
+ If VIRTIO_NET_F_RFS feature bit is negotiated,
+\emph on
+N=max_virtqueue_pairs-1
+\emph default
+, otherwise identify
+\emph on
+N=0
+\emph default
+.
+\change_unchanged
+
\end_layout
\begin_layout Enumerate
@@ -4455,7 +4550,11 @@ status
\end_layout
\begin_layout Enumerate
-The receive virtqueue should be filled with receive buffers.
+The receive virtqueue
+\change_inserted 1986246365 1352743953
+s
+\change_unchanged
+ should be filled with receive buffers.
This is described in detail below in
\begin_inset Quotes eld
\end_inset
@@ -4550,8 +4649,15 @@ Device Operation
\end_layout
\begin_layout Standard
-Packets are transmitted by placing them in the transmitq, and buffers for
- incoming packets are placed in the receiveq.
+Packets are transmitted by placing them in the transmitq
+\change_inserted 1986246365 1353593685
+0..transmitqN
+\change_unchanged
+, and buffers for incoming packets are placed in the receiveq
+\change_inserted 1986246365 1353593692
+0..receiveqN
+\change_unchanged
+.
In each case, the packet itself is preceeded by a header:
\end_layout
@@ -4861,6 +4967,17 @@ If VIRTIO_NET_F_MRG_RXBUF is negotiated, each buffer
must be at least the
struct virtio_net_hdr
\family default
.
+\change_inserted 1986246365 1353594518
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1986246365 1353594638
+If VIRTIO_NET_F_RFS is negotiated, each of the receiveq0...receiveqN that will
+ be used should be populated with receive buffers.
+\change_unchanged
+
\end_layout
\begin_layout Subsection*
@@ -5293,8 +5410,143 @@ Sending VIRTIO_NET_CTRL_ANNOUNCE_ACK command through
control vq.
\end_layout
-\begin_layout Enumerate
+\begin_layout Subsection*
+
+\change_inserted 1986246365 1353593879
+Packet Receive Flow Steering
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1986246365 1353594403
+If the driver negotiates the VIRTIO_NET_F_RFS (depends on
VIRTIO_NET_F_CTRL_VQ),
+ it can transmit outgoing packets on one of the multiple transmitq0..transmitqN
+ and ask the device to queue incoming packets into one the multiple
receiveq0..rec
+eiveqN depending on the packet flow.
+\change_unchanged
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1986246365 1353594292
+\begin_inset listings
+inline false
+status open
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594178
+
+struct virtio_net_ctrl_rfs {
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594212
+
+ u16 virtqueue_pairs;
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594172
+
+};
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594172
+
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594263
+
+#define VIRTIO_NET_CTRL_RFS 1
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594273
+
+ #define VIRTIO_NET_CTRL_RFS_VQ_PAIRS_SET 0
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594273
+
+ #define VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MIN 1
+\end_layout
+
+\begin_layout Plain Layout
+
+\change_inserted 1986246365 1353594273
+
+ #define VIRTIO_NET_CTRL_RFS_VQ_PAIRS_MAX 0x8000
+\end_layout
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1986246365 1353594884
+RFS acceleration is disabled by default.
+ Driver enables RFS by executing the VIRTIO_NET_CTRL_RFS_VQ_PAIRS_SET command,
+ specifying the number of the transmit and receive queues that is going
+ to be used; thus out of transmitq0..transmitqn and receiveq0..receiveqn where
+
+\emph on
+n=virtqueue_pairs-1
+\emph default
+ will be used.
+ All these virtqueues must have been pre-configured in advance.
+ The range of legal values for the
+\emph on
+ virtqueue_pairs
+\emph off
+ field is between 1 and 8000h.
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1986246365 1353595328
+Programming of the receive flow classificator is implicit.
+ Transmitting a packet of a specific flow on transmitqX will cause incoming
+ packets for this flow to be steered to receiveqX.
+ For uni-directional protocols, or where no packets have been transmitted
+ yet, device will steer a packet to a random queue out of the specified
+ receiveq0..receiveqn.
+\change_unchanged
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 1986246365 1353595040
+RFS acceleration is disabled by setting
+\emph on
+virtqueue_pairs = 1
+\emph default
+ (this is the default).
+ Following this, driver should not transmit new packets on virtqueues other
+ than transmitq0 and device will not steer new packets on virtqueues other
+ than receiveq0.
+\change_unchanged
+
+\end_layout
+
+\begin_layout Standard
+
+\change_deleted 1986246365 1353593873
.
+
+\change_unchanged
\end_layout
--
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