[xdp-hints] Re: [PATCH RFC bpf-next 32/52] bpf, cpumap: switch to GRO from netif_receive_skb_list()

["Daniel Xu" <dxu@dxuuu.xyz>]

Hi Lorenzo,

On Thu, Aug 8, 2024, at 12:54 AM, Lorenzo Bianconi wrote:
>> Hi Alexander,
>> 
>> On Tue, Jun 28, 2022, at 12:47 PM, Alexander Lobakin wrote:
>> > cpumap has its own BH context based on kthread. It has a sane batch
>> > size of 8 frames per one cycle.
>> > GRO can be used on its own, adjust cpumap calls to the
>> > upper stack to use GRO API instead of netif_receive_skb_list() which
>> > processes skbs by batches, but doesn't involve GRO layer at all.
>> > It is most beneficial when a NIC which frame come from is XDP
>> > generic metadata-enabled, but in plenty of tests GRO performs better
>> > than listed receiving even given that it has to calculate full frame
>> > checksums on CPU.
>> > As GRO passes the skbs to the upper stack in the batches of
>> > @gro_normal_batch, i.e. 8 by default, and @skb->dev point to the
>> > device where the frame comes from, it is enough to disable GRO
>> > netdev feature on it to completely restore the original behaviour:
>> > untouched frames will be being bulked and passed to the upper stack
>> > by 8, as it was with netif_receive_skb_list().
>> >
>> > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
>> > ---
>> >  kernel/bpf/cpumap.c | 43 ++++++++++++++++++++++++++++++++++++++-----
>> >  1 file changed, 38 insertions(+), 5 deletions(-)
>> >
>> 
>> AFAICT the cpumap + GRO is a good standalone improvement. I think
>> cpumap is still missing this.
>> 
>> I have a production use case for this now. We want to do some intelligent
>> RX steering and I think GRO would help over list-ified receive in some cases.
>> We would prefer steer in HW (and thus get existing GRO support) but not all
>> our NICs support it. So we need a software fallback.
>> 
>> Are you still interested in merging the cpumap + GRO patches?
>
> Hi Daniel and Alex,
>
> Recently I worked on a PoC to add GRO support to cpumap codebase:
> - 
> https://github.com/LorenzoBianconi/bpf-next/commit/a4b8264d5000ecf016da5a2dd9ac302deaf38b3e
>   Here I added GRO support to cpumap through gro-cells.
> - 
> https://github.com/LorenzoBianconi/bpf-next/commit/da6cb32a4674aa72401c7414c9a8a0775ef41a55
>   Here I added GRO support to cpumap trough napi-threaded APIs (with a 
> some
>   changes to them).

Cool! 

>
> Please note I have not run any performance tests so far, just verified it does
> not crash (I was planning to resume this work soon). Please let me know if it
> works for you.

I’ll try to run an A/B test on your two approaches as well as Alex’s. I’ve still
got some testbeds with production traffic going thru them.

Thanks,
Daniel