linux-kernel - Re: [PATCH net] vmxnet3: use gro callback when UPT is enabled

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Date:   Tue, 14 Mar 2023 21:09:19 +0000
From:   Ronak Doshi <doshir@...are.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Pv-drivers <Pv-drivers@...are.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Guolin Yang <gyang@...are.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] vmxnet3: use gro callback when UPT is enabled


> On 3/9/23, 5:02 PM, "Yunsheng Lin" <linyunsheng@...wei.com <mailto:linyunsheng@...wei.com>> wrote:
>
> So it is a run time thing? What happens if some LRO'ed packet is put in the rx queue,
> and the the vnic switches the mode to UPT, is it ok for those LRO'ed packets to go through
> the software GSO processing?
Yes, it should be fine.

> If yes, why not just call napi_gro_receive() for LRO case too?
>
We had done perf measurements in the past and it turned out this results in perf penalty.
See https://patchwork.ozlabs.org/project/netdev/patch/1308947605-4300-1-git-send-email-jesse@nicira.com/

In fact, internally recently we did some perf measurements on RHEL 9.0, and it still showed some penalty.

> Looking closer, it seems vnic is implementing hw GRO from driver' view, as the driver is
> setting skb_shinfo(skb)->gso_* accordingly:
>
>
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Flatest%2Fsource%2Fdrivers%2Fnet%2Fvmxnet3%2Fvmxnet3_drv.c%23L1665&data=05%7C01%7Cdoshir%40vmware.com%7C68e4b3dbd7d948887f0808db21031e2c%>7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C638140069565449054%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=LAw6oCG2MgYH4TPQAnWUy25E2u%2FDMSW2aSJ7OY2%2FOu8%3D&reserved=0 <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Flatest%2Fsource%2Fdrivers%2Fnet%2Fvmxnet3%2Fvmxnet3_drv.c%23L1665&amp;data=05%7C01%7Cdoshir%40vmware.com%7C68e4b3dbd7d948887f0808db21031e2c%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C638140069565449054%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=LAw6oCG2MgYH4TPQAnWUy25E2u%2FDMSW2aSJ7OY2%2FOu8%3D&amp;reserved=0>
>
>
> In that case, you may call napi_gro_receive() for those GRO'ed skb too, see:
>

I see. Seems this got added recently. This will need re-evaluation by the team based on ToT Linux.
But this can be done in near future and as this might take time, for now this patch should be applied as
UPT patches are already up-streamed.

Thanks, 
Ronak