Re: [PATCH bpf-next v2 1/6] resolve_btfids: Deduplicate BTF after btf2btf transformations

On 8/6/26 12:05 PM, Eduard Zingerman wrote:
> On Wed, 2026-08-05 at 16:06 -0700, Ihor Solodrai wrote:
>> btf2btf() adds new types to the BTF: the KF_IMPLICIT_ARGS transform
>> synthesizes an _impl FUNC together with its FUNC_PROTO and copies of the
>> kfunc's decl tags. Nothing deduplicates them afterwards. pahole runs
>> btf__dedup() on its own output, but that happens before resolve_btfids
>> sees the BTF, so any type the tool itself creates is emitted as-is, even
>> when a structurally identical type is already present.
>>
>> Call btf__dedup() at the start of finalize_btf(), so that base
>> distillation and the by-name sort both operate on the canonical set of
>> types.
>>
>> Signed-off-by: Ihor Solodrai <[email protected]>
>> ---
> 
> Hi Ihor,
> 
> I'm curious if you had a chance to measure how this affects the
> resolve_btfids running time?

Yes I did. tl;dr is +30-40% runtime for resolve_btfids:

  0.18424  +- 0.00174  seconds time elapsed  ( +-  0.94% )   without dedup
  0.257003 +- 0.000473 seconds time elapsed  ( +-  0.18% )   with dedup

So that's the bad news.

The good news is that it shouldn't grow, because most of the dedup
time is just walking BTF. We emit very few types.

I think it's worth taking a hit, because a non-normalized kernel BTF
is a petri dish for bugs.