On 03/08/2026 10:06, Amir Ayupov wrote:
--itrace=L adds decoded branch history to existing samples, but a sample that was recorded while the decoder had no trace for that thread keeps an empty branch stack. Consumers of the resulting perf script output, such as profile generators for context-sensitive PGO, have no use for those samples.
Add an opt-in dlfilter that drops samples whose parsed branch stack is empty, so users can exclude them without changing default sample semantics. Build and install it alongside perf's existing dlfilters.
Signed-off-by: Amir Ayupov aaupov@fb.com
tools/perf/Makefile.perf | 1 + .../dlfilters/dlfilter-nonempty-brstack.c | 26 +++++++++++++++++++ 2 files changed, 27 insertions(+) create mode 100644 tools/perf/dlfilters/dlfilter-nonempty-brstack.c
diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf index 0031112c036e8..aeb8085b0756d 100644 --- a/tools/perf/Makefile.perf +++ b/tools/perf/Makefile.perf @@ -427,6 +427,7 @@ PROGRAMS += $(OUTPUT)$(LIBJVMTI) endif DLFILTERS := dlfilter-test-api-v0.so dlfilter-test-api-v2.so dlfilter-show-cycles.so +DLFILTERS += dlfilter-nonempty-brstack.so DLFILTERS := $(patsubst %,$(OUTPUT)dlfilters/%,$(DLFILTERS)) # what 'all' will build and 'install' will install, in perfexecdir diff --git a/tools/perf/dlfilters/dlfilter-nonempty-brstack.c b/tools/perf/dlfilters/dlfilter-nonempty-brstack.c new file mode 100644 index 0000000000000..9e66205b841d5 --- /dev/null +++ b/tools/perf/dlfilters/dlfilter-nonempty-brstack.c @@ -0,0 +1,26 @@ +// SPDX-License-Identifier: GPL-2.0 +/*
- dlfilter-nonempty-brstack.c: Filter out samples with no branch stack
- Copyright (c) 2026, Meta Platforms, Inc.
- */
+#include <stddef.h>
+#include <perf/perf_dlfilter.h>
+int filter_event(void *data, const struct perf_dlfilter_sample *sample, void *ctx) +{
- /* Return 1 to filter out the sample, 0 to keep it */
- return !sample->brstack_nr;
+}
+const char *filter_description(const char **long_description) +{
- static char *long_desc =
"Instruction trace decoders can add branch history to existing ""samples, but samples that were recorded while no trace was ""being collected get an empty branch stack. Filter those out so ""that only samples carrying branch history remain.";- *long_description = long_desc;
- return "Keep only samples with a non-empty branch stack";
+}
Reviewed-by: James Clark james.clark@linaro.org