Re: [PATCHES v3 0/2] perf tools: Add cached probe type detection for evsel

[Namhyung Kim <namhyung@kernel.org>]

On Tue, Jun 16, 2026 at 03:25:44PM -0300, Arnaldo Carvalho de Melo wrote:
> Hi,
> 
> Checking whether an evsel is a kprobe or uprobe currently requires
> walking the PMU list via evsel__find_pmu() on every call.  This is
> wasteful when the same evsel is checked repeatedly in hot paths like
> trace__fprintf_tp_fields().
> 
> Patch 1 adds evsel__is_kprobe(), evsel__is_uprobe(), and
> evsel__is_probe() helpers that resolve the probe type on first call
> and cache the result in a 3-bit field that fits in existing struct
> padding.
> 
> Detection covers both PMU-based probes (kprobe/uprobe PMU, detected
> by PMU name) and ftrace-based dynamic probes (kprobes/uprobes/fprobes
> created via tracefs, which report as PMU "tracepoint").  Ftrace probes
> are detected by the __probe_ip field that the kernel adds to all
> dynamic probe formats — this is authoritative regardless of the
> group/system name the user chose.
> 
> Patch 2 is the first user: it guards the __probe_ip field name
> comparison in perf trace with evsel__is_probe(), so the strcmp is
> skipped entirely for the common case of non-probe tracepoint events.
> 
> Patch 3 adds inline stubs for evsel__field() and evsel__common_field()
> when libtraceevent is absent.  These were previously declared
> unconditionally but defined only inside #ifdef HAVE_LIBTRACEEVENT,
> which was harmless until patch 1 added a call from always-compiled
> code in evsel.c.
> 
> Build-tested with gcc and clang.
> 
> Changes in v3:
>   - Add patch 3: no-libtraceevent stubs for evsel__field() and
>     evsel__common_field().  Without this, NO_LIBTRACEEVENT=1 builds
>     fail to link because evsel__resolve_probe_type() calls
>     evsel__field() unconditionally (sashiko-bot).
> 
> Changes in v2 (patch 1 only):
>   - Detect ftrace-based dynamic probes (kprobes/uprobes/fprobes created
>     via tracefs) that report PMU "tracepoint" instead of "kprobe"/
>     "uprobe".  Check for the __probe_ip field presence in the tracepoint
>     format.  Without this, evsel__is_probe() returned false for ftrace
>     probes, breaking __probe_ip suppression in perf trace for probes
>     created via 'perf probe' (sashiko-bot).
>   - Widen probe_type bitfield from 2 to 3 bits for PROBE__FTRACE.
> 
> Arnaldo Carvalho de Melo (3):
>   perf evsel: Add lazy-initialized probe type detection helpers
>   perf trace: Guard __probe_ip suppression with evsel__is_probe()
>   perf evsel: Add no-libtraceevent stubs for evsel__field() and evsel__common_field()

It seems you squashed patch 3 into 1. :)

Thanks,
Namhyung

> 
>  tools/perf/builtin-trace.c |  2 +-
>  tools/perf/util/evsel.c    | 53 ++++++++++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/evsel.h    | 19 +++++++++++++++++
>  3 files changed, 73 insertions(+), 1 deletion(-)
> 
> Cc: Aaron Tomlin <atomlin@atomlin.com>
> Cc: Ian Rogers <irogers@google.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> 
> Developed with AI assistance (Claude/sashiko), tagged in commits.