netdev - Re: net: tso: add UDP segmentation support: adds regression for ax200 upload

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Date:   Thu, 17 Dec 2020 11:11:37 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Ben Greear <greearb@...delatech.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: net: tso: add UDP segmentation support: adds regression for ax200 upload

On Thu, Dec 17, 2020 at 12:59 AM Ben Greear <greearb@...delatech.com> wrote:
>
> On 12/16/20 3:09 PM, Ben Greear wrote:
> > Hello Eric,
> >
> > The patch below evidently causes TCP throughput to be about 50Mbps instead of 700Mbps
> > when using ax200 to upload tcp traffic.
> >
> > When I disable TSO, performance goes back up to around 700Mbps.
>
> As a followup, when I revert the patch, upload speed goes to ~900Mbps,
> so even better than just disabling TSO (I left TSO enabled after reverting the patch).
>
> Thanks,
> Ben
>

Thanks for the report !

It seems drivers/net/wireless/intel/iwlwifi/pcie/tx.c:iwl_fill_data_tbs_amsdu()
calls tso_build_hdr() with extra bytes (SNAP header),
it is not yet clear to me what is broken :/

Can you confirm which driver is used for ax200 ?

I see tso_build_hdr() also being used from
drivers/net/wireless/intel/iwlwifi/queue/tx.c