Re: [PATCH net-next v2 03/14] bpf: Make BPF skb extension survive packet scrubbing

[Jakub Sitnicki <jakub@cloudflare.com>]

On Wed, Sep 30, 2026 at 09:00 AM GMT, Alexei Starovoitov wrote:
> On Tue Sep 29, 2026 at 8:32 PM UTC, Jakub Sitnicki wrote:
>> Everything pushed to:
>>
>> https://github.com/jsitnicki/skb-metadata-bench/tree/main/profile
>
> looks like you had lockdep on, so all the data and conclusions
> likely do not correlate to production.
> Pls fix and remeasure everything.

Thanks. This makes much more sense now.

1) Lockdep was on. Fixed. Configs published to [1].

2) Switched from mpstat to bpf_stats since bpf-skb-ext cost was so low
now that it was drowning in the noise. skb extension teardown is not
accounted for.

3) With rhash, I noticed churn from auto-shrinking in map_update_elem
(can be seen in gtpchurn profile [2]). LLM suggested a one-line fix to
set min_size from map_extra hint. Benchmarks ran with this patch [3].

New results (prog runtime from bpf_stats in nsec):

 ~/bench $ just bpfstats
python3 tools/bpfstats.py --agg results-1 results-2 results-3
variant          prog              results-1  results-2  results-3    total mean ± spread
-------------------------------------------------------------------------------------------
ext-cnt          cnt_ingress            35.9       35.6       35.5      106.7 ± 2.2
                 cnt_egress             70.3       73.5       69.2

ext-ext          ext_write             199.3      198.9      203.0      263.8 ± 1.9
                 ext_read               63.1       64.1       63.2

gtp-cnt          cnt_ingress            34.4       34.3       34.6       94.6 ± 2.5
                 cnt_egress             59.9       58.1       62.7

gtp-gtp          gtp_write             531.0      555.9      567.2      920.9 ± 34.5
                 gtp_read               85.1       87.5       91.2
                 gtp_skb_free          267.1      283.9      293.9

gtp-gtpchurn     gtp_write             784.9      782.6      830.6     1190.8 ± 44.2
                 gtp_read               82.5       82.3       88.6
                 gtp_skb_free          297.5      294.7      328.7

gtp-gtplru       gtplru_write          394.9      391.9      394.5      542.8 ± 1.1
                 gtplru_read            48.2       49.4       48.9
                 gtplru_skb_free        99.9      100.4      100.5

gtp-gtp is with nelem_hint+min_size hint set.
gtp-gtpchurn is without it (map_extra=0).
perf reports and flamegraphs also updated [4].

[1] https://github.com/jsitnicki/skb-metadata-bench/tree/main/configs
[2] https://raw.githubusercontent.com/jsitnicki/skb-metadata-bench/refs/heads/main/profile/perf.gtp-gtpchurn.svg
[3] https://github.com/jsitnicki/skb-metadata-bench/blob/main/patches/rht-no-shrink-churn.patch
[4] https://github.com/jsitnicki/skb-metadata-bench/tree/main/profile