netdev - Re: [PATCH net-next 1/2] selftests/net: GRO coalesce test

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Date:   Thu, 05 Aug 2021 13:16:37 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Coco Li <lixiaoyan@...gle.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next 1/2] selftests/net: GRO coalesce test

Hello,

On Thu, 2021-08-05 at 07:36 +0000, Coco Li wrote:
> Implement a GRO testsuite that expects Linux kernel GRO behavior.
> All tests pass with the kernel software GRO stack. Run against a device
> with hardware GRO to verify that it matches the software stack.
> 
> gro.c generates packets and sends them out through a packet socket. The
> receiver in gro.c (run separately) receives the packets on a packet
> socket, filters them by destination ports using BPF and checks the
> packet geometry to see whether GRO was applied.
> 
> gro.sh provides a wrapper to run the gro.c in NIC loopback mode.
> It is not included in continuous testing because it modifies network
> configuration around a physical NIC: gro.sh sets the NIC in loopback
> mode, creates macvlan devices on the physical device in separate
> namespaces, and sends traffic generated by gro.c between the two
> namespaces to observe coalescing behavior.

I like this idea a lot!

Have you considered additionally run the same test of top of a veth
pair, and have such tests always enabled, so we could have some
coverage regardless of specific H/W available?

To do the above you should disable TSO on the veth sender peer and
enable GRO on the other end.

[...]
> +  setup_ns
> +  # Each test is run 3 times to deflake, because given the receive timing,
> +  # not all packets that should coalesce will be considered in the same flow
> +  # on every try.

I thought that tuning 'gro_flush_timeout' appropriatelly, you should be
able to control exactly which packets will be aggregated ???

Thanks!

Paolo