netdev - Re: [PATCHv4] virtio-spec: virtio network device RFS support

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Message-ID: <20121123101001.GA7051@redhat.com>
Date:	Fri, 23 Nov 2012 12:10:02 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	rusty@...tcorp.com.au, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCHv4] virtio-spec: virtio network device RFS support

On Fri, Nov 23, 2012 at 01:17:36PM +0800, Jason Wang wrote:
...

> "specifying the number of the last transmit and receive queue that
> is going to be used; thus out of transmitq0..transmitqn and
> receiveq0..receiveqn where n=virtqueue_pairs will be used."
> 
> In this description, looks like n+1 virtqueue pairs (include
> receiveq0 and transmitq0) could be used in RFS mode.

The intent was not to reserve any virt queue pairs.
I hope I clarified this below.



Thanks for the comments. Here's an incremental patch to address
them.


diff --git a/virtio-spec.lyx b/virtio-spec.lyx
index e562335..53ddeec 100644
--- a/virtio-spec.lyx
+++ b/virtio-spec.lyx
@@ -4384,7 +4384,7 @@ VIRTIO_NET_F_GUEST_ANNOUNCE(21) Guest can send gratuitous packets.
 \begin_layout Description
 
 \change_inserted 1986246365 1352742808
-VIRTIO_NET_F_RFS(2) Device supports Receive Flow Steering.
+VIRTIO_NET_F_RFS(22) Device supports Receive Flow Steering.
 \change_unchanged
 
 \end_layout
@@ -4432,9 +4432,10 @@ N
 \emph default
 =
 \emph on
-max_virtqueue_pairs
+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
  
@@ -4496,7 +4497,7 @@ The initialization routine should identify the receive and transmission
 \change_inserted 1986246365 1352743942
  If VIRTIO_NET_F_RFS feature bit is negotiated, 
 \emph on
-N=max_virtqueue_pairs
+N=max_virtqueue_pairs-1
 \emph default
 , otherwise identify 
 \emph on
@@ -5464,7 +5465,7 @@ struct virtio_net_ctrl_rfs {
 
 \change_inserted 1986246365 1353594263
 
-#define VIRTIO_NET_CTRL_RFC    1
+#define VIRTIO_NET_CTRL_RFS    1
 \end_layout
 
 \begin_layout Plain Layout
@@ -5474,6 +5475,19 @@ struct virtio_net_ctrl_rfs {
  #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
 
 
@@ -5484,14 +5498,19 @@ struct virtio_net_ctrl_rfs {
 \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 last transmit and receive queue that is going
+ 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
+n=virtqueue_pairs-1
 \emph default
-_pairs will be used.
+ 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
@@ -5512,7 +5531,7 @@ Programming of the receive flow classificator is implicit.
 \change_inserted 1986246365 1353595040
 RFS acceleration is disabled by setting 
 \emph on
-virtqueue_pairs = 0
+virtqueue_pairs = 1
 \emph default
  (this is the default).
  Following this, driver should not transmit new packets on virtqueues other
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