Re: [PATCH v2 net-next] net: dsa: add GRO support via gro_cells

[David Miller <davem@davemloft.net>]

From: Alexander Lobakin <bloodyreaper@yandex.ru>
Date: Tue, 21 Apr 2020 16:41:08 +0300

> gro_cells lib is used by different encapsulating netdevices, such as
> geneve, macsec, vxlan etc. to speed up decapsulated traffic processing.
> CPU tag is a sort of "encapsulation", and we can use the same mechs to
> greatly improve overall DSA performance.
> skbs are passed to the GRO layer after removing CPU tags, so we don't
> need any new packet offload types as it was firstly proposed by me in
> the first GRO-over-DSA variant [1].
> 
> The size of struct gro_cells is sizeof(void *), so hot struct
> dsa_slave_priv becomes only 4/8 bytes bigger, and all critical fields
> remain in one 32-byte cacheline.
> The other positive side effect is that drivers for network devices
> that can be shipped as CPU ports of DSA-driven switches can now use
> napi_gro_frags() to pass skbs to kernel. Packets built that way are
> completely non-linear and are likely being dropped without GRO.
> 
> This was tested on to-be-mainlined-soon Ethernet driver that uses
> napi_gro_frags(), and the overall performance was on par with the
> variant from [1], sometimes even better due to minimal overhead.
> net.core.gro_normal_batch tuning may help to push it to the limit
> on particular setups and platforms.
> 
> iperf3 IPoE VLAN NAT TCP forwarding (port1.218 -> port0) setup
> on 1.2 GHz MIPS board:
 ...
> v2:
>  - Add some performance examples in the commit message;
>  - No functional changes.
> 
> [1] https://lore.kernel.org/netdev/20191230143028.27313-1-alobakin@dlink.ru/
> 
> Signed-off-by: Alexander Lobakin <bloodyreaper@yandex.ru>

Applied, thank you.