Currently, vmxnet3 uses GRO callback only if LRO is disabled. However,
on smartNic based setups where UPT is supported, LRO can be enabled
from guest VM but UPT devicve does not support LRO as of now. In such
cases, there can be performance degradation as GRO is not being done.

This patch fixes this issue by calling GRO API when UPT is enabled. We
use updateRxProd to determine if UPT mode is active or not.

To clarify few things discussed over the thread:
The patch is not neglecting any feature bits nor disabling GRO. It uses
GRO callback when UPT is active as LRO is not available in UPT.
GRO callback cannot be used as default for all cases as it degrades
performance for non-UPT cases or for cases when LRO is already done in
ESXi.

Cc: stable@vger.kernel.org
Fixes: 6f91f4ba046e ("vmxnet3: add support for capability registers")
Signed-off-by: Ronak Doshi <doshir@vmware.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
--
v1->v2: split if check on multiple lines
---
 drivers/net/vmxnet3/vmxnet3_drv.c |   4 +++-
 1 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c
index 682987040ea8..da488cbb0542 100644
--- a/drivers/net/vmxnet3/vmxnet3_drv.c
+++ b/drivers/net/vmxnet3/vmxnet3_drv.c
@@ -1688,7 +1688,9 @@ vmxnet3_rq_rx_complete(struct vmxnet3_rx_queue *rq,
 			if (unlikely(rcd->ts))
 				__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), rcd->tci);
 
-			if (adapter->netdev->features & NETIF_F_LRO)
+			/* Use GRO callback if UPT is enabled */
+			if ((adapter->netdev->features & NETIF_F_LRO) &&
+			    !rq->shared->updateRxProd)
 				netif_receive_skb(skb);
 			else
 				napi_gro_receive(&rq->napi, skb);
-- 
2.11.0

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 23 Mar 2023 13:07:21 -0700 you wrote:
> Currently, vmxnet3 uses GRO callback only if LRO is disabled. However,
> on smartNic based setups where UPT is supported, LRO can be enabled
> from guest VM but UPT devicve does not support LRO as of now. In such
> cases, there can be performance degradation as GRO is not being done.
> 
> This patch fixes this issue by calling GRO API when UPT is enabled. We
> use updateRxProd to determine if UPT mode is active or not.
> 
> [...]

Here is the summary with links:
  - [net,v2] vmxnet3: use gro callback when UPT is enabled
    https://git.kernel.org/netdev/net/c/3bced313b9a5

You are awesome, thank you!
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