linux-kernel - Re: [PATCH 2/2] tracing: resolve enum names for function arguments via BTF

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Message-ID: <CAErzpmsjt7=EsLZfSMALRTM9ZBKPDYWGWE9__w49OTk_VL+4hA@mail.gmail.com>
Date: Wed, 4 Feb 2026 22:16:24 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: andrii.nakryiko@...il.com, ast@...nel.org, mhiramat@...nel.org, 
	linux-kernel@...r.kernel.org, Donglin Peng <pengdonglin@...omi.com>, 
	linux-trace-kernel@...r.kernel.org, bpf <bpf@...r.kernel.org>, 
	Eduard Zingerman <eddyz87@...il.com>
Subject: Re: [PATCH 2/2] tracing: resolve enum names for function arguments
 via BTF

On Tue, Feb 3, 2026 at 11:16 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 3 Feb 2026 21:50:47 +0800
> Donglin Peng <dolinux.peng@...il.com> wrote:
>
> > Testing revealed that sorting within resolve_btfids introduces issues with
> > btf__dedup. Therefore, I plan to move the sorting logic directly into
> > btf__add_enum_value and btf__add_enum64_value in libbpf, which are
> > invoked by pahole. However, it means that we need a newer pahole
> > version.
>
> Sorting isn't a requirement just something I wanted to bring up. If it's
> too complex and doesn't achieve much benefit then let's not do it.

Thanks for clarifying. Analysis shows most enum-type btf_type have
small vlen (78% ≤ 10, 95% ≤50), so I think that  linear search could
be acceptable.

>
> My worry is because "cat trace" takes quite a long time just reading the
> BTF arguments. I'm worried it will just get worse with enums as well.

The delay stems from `btf_find_by_name_kind`’s linear search over
vmlinux BTF (10k+ types). This was resolved by adding binary search
to `btf_find_by_name_kind` [1].

Performance tests [2] confirm the improvement:
1. Original funcgraph-retval:
# time cat trace | wc -l
101024

real    0m0.682s
user    0m0.000s
sys     0m0.695s

2. Enhanced funcgraph-retval:
# time cat trace | wc -l
99326

real    0m12.886s
user    0m0.010s
sys     0m12.680s

3. Enhanced funcgraph-retval + optimizined btf_find_by_name_kind:
# time cat trace | wc -l
102922

real    0m0.794s
user    0m0.000s
sys     0m0.810s

Binary search reduces overhead to near-negligible levels (0.794s vs. 12.886s).

[1] https://lore.kernel.org/bpf/20260109130003.3313716-1-dolinux.peng@gmail.com/
[2] https://lore.kernel.org/lkml/20251209121349.525641-1-dolinux.peng@gmail.com/

>
> I have trace-cmd reading BTF now (just haven't officially released it) and
> doing an extract and reading the trace.dat file is much faster than reading
> the trace file with arguments. I'll need to implement the enum logic too in
> libtraceevent.
>
> -- Steve