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

Daniel Xu
2024-08-21T00:29:52Z

Hi Olek,

On Mon, Aug 19, 2024 at 04:50:52PM GMT, Alexander Lobakin wrote:
[..]
> > Thanks A LOT for doing this benchmarking!
>
> I optimized the code a bit and picked my old patches for bulk NAPI skb
> cache allocation and today I got 4.7 Mpps 🎉
> IOW, the result of the series (7 patches totally, but 2 are not
> networking-related) is 2.7 -> 4.7 Mpps == 75%!
>
> Daniel,
>
> if you want, you can pick my tree[0], either full or just up to
>
> "bpf: cpumap: switch to napi_skb_cache_get_bulk()"
>
> (13 patches total: 6 for netdev_feature_t and 7 for the cpumap)
>
> and test with your usecases. Would be nice to see some real world
> results, not my synthetic tests :D
>
> > --Jesper
>
> [0]
> https://github.com/alobakin/linux/compare/idpf-libie-new~52...idpf-libie-new/

So it turns out keeping the workload in place while I update and reboot
the kernel is a Hard Problem. I'll put in some more effort and see if I
can get one of the workloads to stay still, but it'll be a somewhat
noisy test even if it works. So the following are synthetic tests
(neper) but on a real prod setup as far as container networking and
configuration is concerned.

I cherry-picked 586be610~1..ca22ac8e9de onto our 6.9-ish branch. Had to
skip some of the flag refactors b/c of conflicts - I didn't know the
code well enough to do fixups. So I had to apply this diff (FWIW not sure
the struct_size() here was right anyhow):

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 089d19c62efe..359fbfaa43eb 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -110,7 +110,7 @@ static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
if (!cmap->cpu_map)
goto free_cmap;

- dev = bpf_map_area_alloc(struct_size(dev, priv, 0), NUMA_NO_NODE);
+ dev = bpf_map_area_alloc(sizeof(*dev), NUMA_NO_NODE);
if (!dev)
goto free_cpu_map;

==== Baseline ===
./tcp_rr -c -H $SERVER -p 50,90,99 -T4 -F8 -l30 ./tcp_stream -c -H $SERVER -T8 -F16 -l30

Transactions Latency P50 (s) Latency P90 (s) Latency P99 (s) Throughput (Mbit/s)
Run 1 2578189 0.00008831 0.00010623 0.00013439 Run 1 15427.22
Run 2 2657923 0.00008575 0.00010239 0.00012927 Run 2 15272.12
Run 3 2700402 0.00008447 0.00010111 0.00013183 Run 3 14871.35
Run 4 2571739 0.00008575 0.00011519 0.00013823 Run 4 15344.72
Run 5 2476427 0.00008703 0.00013055 0.00016895 Run 5 15193.2
Average 2596936 0.000086262 0.000111094 0.000140534 Average 15221.722

=== cpumap NAPI patches ===
Transactions Latency P50 (s) Latency P90 (s) Latency P99 (s) Throughput (Mbit/s)
Run 1 2554598 0.00008703 0.00011263 0.00013055 Run 1 17090.29
Run 2 2478905 0.00009087 0.00011391 0.00014463 Run 2 16742.27
Run 3 2418599 0.00009471 0.00011007 0.00014207 Run 3 17555.3
Run 4 2562463 0.00008959 0.00010367 0.00013055 Run 4 17892.3
Run 5 2716551 0.00008127 0.00010879 0.00013439 Run 5 17578.32
Average 2546223.2 0.000088694 0.000109814 0.000136438 Average 17371.696
Delta -1.95% 2.82% -1.15% -2.91% 14.12%

So it looks like the GRO patches work quite well out of the box. It's
curious that tcp_rr transactions go down a bit, though. I don't have any
intuition around that.

Lemme know if you wanna change some stuff and get a rerun.

Thanks,
Daniel