From: Shachar Raindel <[email protected]>
The batching logic in netvsc_send is non-trivial, due to
a combination of the Linux API and the underlying hypervisor
interface. Add a comment explaining why the code is written this
way.
Signed-off-by: Shachar Raindel <[email protected]>
Signed-off-by: Haiyang Zhang <[email protected]>
---
.../ethernet/microsoft/netvsc.rst | 14 ++++++++-----
drivers/net/hyperv/netvsc.c | 20 +++++++++++++++++++
2 files changed, 29 insertions(+), 5 deletions(-)
diff --git a/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst b/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst
index c3f51c672a68..fc5acd427a5d 100644
--- a/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst
+++ b/Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst
@@ -87,11 +87,15 @@ Receive Buffer
contain one or more packets. The number of receive sections may be changed
via ethtool Rx ring parameters.
- There is a similar send buffer which is used to aggregate packets for sending.
- The send area is broken into chunks of 6144 bytes, each of section may
- contain one or more packets. The send buffer is an optimization, the driver
- will use slower method to handle very large packets or if the send buffer
- area is exhausted.
+ There is a similar send buffer which is used to aggregate packets
+ for sending. The send area is broken into chunks, typically of 6144
+ bytes, each of section may contain one or more packets. Small
+ packets are usually transmitted via copy to the send buffer. However,
+ if the buffer is temporarily exhausted, or the packet to be transmitted is
+ an LSO packet, the driver will provide the host with pointers to the data
+ from the SKB. This attempts to achieve a balance between the overhead of
+ data copy and the impact of remapping VM memory to be accessible by the
+ host.
XDP support
-----------
diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index dc3f73c3b33e..dc333dceb055 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1006,6 +1006,26 @@ static inline void move_pkt_msd(struct hv_netvsc_packet **msd_send,
}
/* RCU already held by caller */
+/* Batching/bouncing logic is designed to attempt to optimize
+ * performance.
+ *
+ * For small, non-LSO packets we copy the packet to a send buffer
+ * which is pre-registered with the Hyper-V side. This enables the
+ * hypervisor to avoid remapping the aperture to access the packet
+ * descriptor and data.
+ *
+ * If we already started using a buffer and the netdev is transmitting
+ * a burst of packets, keep on copying into the buffer until it is
+ * full or we are done collecting a burst. If there is an existing
+ * buffer with space for the RNDIS descriptor but not the packet, copy
+ * the RNDIS descriptor to the buffer, keeping the packet in place.
+ *
+ * If we do batching and send more than one packet using a single
+ * NetVSC message, free the SKBs of the packets copied, except for the
+ * last packet. This is done to streamline the handling of the case
+ * where the last packet only had the RNDIS descriptor copied to the
+ * send buffer, with the data pointers included in the NetVSC message.
+ */
int netvsc_send(struct net_device *ndev,
struct hv_netvsc_packet *packet,
struct rndis_message *rndis_msg,
--
2.25.1
> From: LKML haiyangz <[email protected]> On Behalf Of Haiyang Zhang
> Sent: Friday, March 12, 2021 3:45 PM
> To: [email protected]; [email protected]
> Cc: Haiyang Zhang <[email protected]>; KY Srinivasan
> <[email protected]>; Stephen Hemminger <[email protected]>;
> [email protected]; vkuznets <[email protected]>; [email protected];
> [email protected]; Shachar Raindel <[email protected]>
> Subject: [PATCH net-next] hv_netvsc: Add a comment clarifying batching logic
>
> From: Shachar Raindel <[email protected]>
>
> The batching logic in netvsc_send is non-trivial, due to
> a combination of the Linux API and the underlying hypervisor
> interface. Add a comment explaining why the code is written this
> way.
>
> Signed-off-by: Shachar Raindel <[email protected]>
> Signed-off-by: Haiyang Zhang <[email protected]>
> ---
Reviewed-by: Dexuan Cui <[email protected]>
Hello:
This patch was applied to netdev/net-next.git (refs/heads/master):
On Fri, 12 Mar 2021 15:45:27 -0800 you wrote:
> From: Shachar Raindel <[email protected]>
>
> The batching logic in netvsc_send is non-trivial, due to
> a combination of the Linux API and the underlying hypervisor
> interface. Add a comment explaining why the code is written this
> way.
>
> [...]
Here is the summary with links:
- [net-next] hv_netvsc: Add a comment clarifying batching logic
https://git.kernel.org/netdev/net-next/c/bd49fea7586b
You are awesome, thank you!
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