Re: [PATCH bpf-next v3] selftests/bpf: Add LPM trie microbenchmarks

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 28/07/2025 16.34, Alexei Starovoitov wrote:
>> diff --git a/tools/testing/selftests/bpf/progs/lpm_trie_bench.c b/tools/testing/selftests/bpf/progs/lpm_trie_bench.c
>> new file mode 100644
>> index 000000000000..522e1cbef490
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/lpm_trie_bench.c
[...]
>> +
>> +static void gen_random_key(struct trie_key *key)
>> +{
>> +       key->prefixlen = prefixlen;
>> +       key->data = bpf_get_prandom_u32() % nr_entries;
> bpf_get_prandom_u32() is not free
> and modulo operation isn't free either.
> The benchmark includes their time.
> It's ok to have it, but add a mode where the bench
> tests linear lookup/update too with simple key.data++

I've extended this bench with a "noop" and "baseline" benchmark[1].

  [1] 
https://lore.kernel.org/all/175509897596.2755384.18413775753563966331.stgit@firesoul/

This allowed us to measure and deduce that the:
   bpf_get_prandom_u32() % nr_entries

Takes 14.1 nanosec for doing the rand + modulo.

The "noop" test shows harness overhead is 13.402 ns/op
and on-top the "baseline" shows randomness takes 27.529 ns/op.

--Jesper