[PATCH v9 2/9] perf cs-etm: Filter synthesized branch samples
Leo Yan
leo.yan at arm.com
Tue Jun 16 07:51:10 PDT 2026
From: Leo Yan <leo.yan at linaro.org>
The itrace 'c' and 'r' options request synthesized branch events for
calls and returns only. For perf script the default itrace options are
"--itrace=ce", so CS ETM should emit call branches and error events by
default.
CS ETM currently synthesizes a branch sample for every decoded taken
branch whenever branch synthesis is enabled. This produces redundant
jump and conditional branch samples.
Add a branch filter derived from the itrace calls and returns options.
When neither option is set, keep the existing behavior and synthesize all
branch samples. When calls or returns are requested, emit only branch
samples whose flags match the selected branch type, while preserving trace
begin/end markers.
Also update test_arm_coresight_disasm.sh and arm-cs-trace-disasm.py
to use the --itrace=b option for generating branch samples.
Before:
perf script -F,+flags
callchain_test 6114 [005] 331519.825214: 1 branches: tr strt jmp 0 [unknown] ([unknown]) => ffff8000803a3a68 perf_report_aux_output_id+0x50 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff8000803a3a74 perf_report_aux_output_id+0x5c ([kernel.kallsyms]) => ffff8000817f4d88 memset+0x0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jmp ffff8000817f4d8c memset+0x4 ([kernel.kallsyms]) => ffff8000817f4c00 __pi_memset_generic+0x0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000817f4c1c __pi_memset_generic+0x1c ([kernel.kallsyms]) => ffff8000817f4c44 __pi_memset_generic+0x44 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000817f4c4c __pi_memset_generic+0x4c ([kernel.kallsyms]) => ffff8000817f4c5c __pi_memset_generic+0x5c ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000817f4c5c __pi_memset_generic+0x5c ([kernel.kallsyms]) => ffff8000817f4cf0 __pi_memset_generic+0xf0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000817f4d30 __pi_memset_generic+0x130 ([kernel.kallsyms]) => ffff8000817f4d68 __pi_memset_generic+0x168 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000817f4d78 __pi_memset_generic+0x178 ([kernel.kallsyms]) => ffff8000817f4d6c __pi_memset_generic+0x16c ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000817f4d78 __pi_memset_generic+0x178 ([kernel.kallsyms]) => ffff8000817f4d6c __pi_memset_generic+0x16c ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000817f4d78 __pi_memset_generic+0x178 ([kernel.kallsyms]) => ffff8000817f4d6c __pi_memset_generic+0x16c ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: return ffff8000817f4d84 __pi_memset_generic+0x184 ([kernel.kallsyms]) => ffff8000803a3a78 perf_report_aux_output_id+0x60 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: jcc ffff8000803a3a98 perf_report_aux_output_id+0x80 ([kernel.kallsyms]) => ffff8000803a3b04 perf_report_aux_output_id+0xec ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff8000803a3b1c perf_report_aux_output_id+0x104 ([kernel.kallsyms]) => ffff8000803a38f8 __perf_event_header__init_id+0x0 ([kernel.kallsyms])
After:
callchain_test 6114 [005] 331519.825214: 1 branches: tr strt jmp 0 [unknown] ([unknown]) => ffff8000803a3a68 perf_report_aux_output_id+0x50 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff8000803a3a74 perf_report_aux_output_id+0x5c ([kernel.kallsyms]) => ffff8000817f4d88 memset+0x0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff8000803a3b1c perf_report_aux_output_id+0x104 ([kernel.kallsyms]) => ffff8000803a38f8 __perf_event_header__init_id+0x0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff8000803a39c0 __perf_event_header__init_id+0xc8 ([kernel.kallsyms]) => ffff800080105258 __task_pid_nr_ns+0x0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff80008010528c __task_pid_nr_ns+0x34 ([kernel.kallsyms]) => ffff8000801d5610 __rcu_read_lock+0x0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff8000801052b0 __task_pid_nr_ns+0x58 ([kernel.kallsyms]) => ffff800080192078 lock_acquire+0x0 ([kernel.kallsyms])
callchain_test 6114 [005] 331519.825214: 1 branches: call ffff8000801923f4 lock_acquire+0x37c ([kernel.kallsyms]) => ffff8000801d6da0 rcu_is_watching+0x0 ([kernel.kallsyms])
Fixes: b12235b113cf ("perf tools: Add mechanic to synthesise CoreSight trace packets")
Signed-off-by: Leo Yan <leo.yan at linaro.org>
Reviewed-by: James Clark <james.clark at linaro.org>
Signed-off-by: Leo Yan <leo.yan at arm.com>
---
tools/perf/scripts/python/arm-cs-trace-disasm.py | 9 +++++----
.../tests/shell/coresight/test_arm_coresight_disasm.sh | 4 ++--
tools/perf/util/cs-etm.c | 15 +++++++++++++++
3 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/tools/perf/scripts/python/arm-cs-trace-disasm.py b/tools/perf/scripts/python/arm-cs-trace-disasm.py
index 8f6fa4a007b42fcc98e71b74b36ba3a61d7acb2f..42579f8586842704d3800ad731d4609d2bb968da 100755
--- a/tools/perf/scripts/python/arm-cs-trace-disasm.py
+++ b/tools/perf/scripts/python/arm-cs-trace-disasm.py
@@ -31,18 +31,19 @@ from perf_trace_context import perf_sample_srccode, perf_config_get
#
# Output disassembly with objdump and auto detect vmlinux
# (when running on same machine.):
-# perf script -s scripts/python/arm-cs-trace-disasm.py -d
+# perf script --itrace=b -s scripts/python/arm-cs-trace-disasm.py \
+# -- -d
#
# Output disassembly with llvm-objdump:
-# perf script -s scripts/python/arm-cs-trace-disasm.py \
+# perf script --itrace=b -s scripts/python/arm-cs-trace-disasm.py \
# -- -d llvm-objdump-11 -k path/to/vmlinux
#
# Output accurate disassembly by passing kcore to script:
-# perf script -s scripts/python/arm-cs-trace-disasm.py \
+# perf script --itrace=b -s scripts/python/arm-cs-trace-disasm.py \
# -- -d -k perf.data/kcore_dir/kcore
#
# Output only source line and symbols:
-# perf script -s scripts/python/arm-cs-trace-disasm.py
+# perf script --itrace=b -s scripts/python/arm-cs-trace-disasm.py
def default_objdump():
config = perf_config_get("annotate.objdump")
diff --git a/tools/perf/tests/shell/coresight/test_arm_coresight_disasm.sh b/tools/perf/tests/shell/coresight/test_arm_coresight_disasm.sh
index ccb90dda24758522be12cba27140abc9b60d8261..f3ebad5963783e9ae74be5b046d20c3f2e01a5a1 100755
--- a/tools/perf/tests/shell/coresight/test_arm_coresight_disasm.sh
+++ b/tools/perf/tests/shell/coresight/test_arm_coresight_disasm.sh
@@ -44,7 +44,7 @@ branch_search='[[:space:]](bl|b(\.(eq|ne|cs|cc|mi|pl|vs|vc|hi|ls|ge|lt|gt|le|al)
if [ "$(id -u)" == 0 ] && [ -e /proc/kcore ]; then
echo "Testing kernel disassembly"
perf record -o ${perfdata} -e cs_etm//k --kcore -Se -m,64K -- touch $file > /dev/null 2>&1
- perf script -i ${perfdata} -s python:${script_path} -- \
+ perf script -i ${perfdata} --itrace=b -s python:${script_path} -- \
-d --stop-sample=2 -k ${perfdata}/kcore_dir/kcore 2> /dev/null > ${file}
grep -q -E ${branch_search} ${file}
echo "Found kernel branches"
@@ -56,7 +56,7 @@ fi
## Test user ##
echo "Testing userspace disassembly"
perf record -o ${perfdata} -e cs_etm//u -Se -m,64K -- touch $file > /dev/null 2>&1
-perf script -i ${perfdata} -s python:${script_path} -- \
+perf script -i ${perfdata} --itrace=b -s python:${script_path} -- \
-d --stop-sample=2 2> /dev/null > ${file}
grep -q -E ${branch_search} ${file}
echo "Found userspace branches"
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index d484a6155c2c22fa916d0365987302f6bb9978e9..42de2d82fd728bcc719adcab80670efa9859762f 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -71,6 +71,7 @@ struct cs_etm_auxtrace {
int num_cpu;
u64 latest_kernel_timestamp;
u32 auxtrace_type;
+ u32 branches_filter;
u64 branches_sample_type;
u64 branches_id;
u64 instructions_sample_type;
@@ -1686,6 +1687,10 @@ static int cs_etm__synth_branch_sample(struct cs_etm_queue *etmq,
} dummy_bs;
u64 ip;
+ if (etm->branches_filter &&
+ !(etm->branches_filter & tidq->prev_packet->flags))
+ return 0;
+
ip = cs_etm__last_executed_instr(tidq->prev_packet);
event->sample.header.type = PERF_RECORD_SAMPLE;
@@ -3528,6 +3533,16 @@ int cs_etm__process_auxtrace_info_full(union perf_event *event,
etm->synth_opts.callchain = false;
}
+ if (etm->synth_opts.calls)
+ etm->branches_filter |= PERF_IP_FLAG_CALL |
+ PERF_IP_FLAG_TRACE_BEGIN |
+ PERF_IP_FLAG_TRACE_END;
+
+ if (etm->synth_opts.returns)
+ etm->branches_filter |= PERF_IP_FLAG_RETURN |
+ PERF_IP_FLAG_TRACE_BEGIN |
+ PERF_IP_FLAG_TRACE_END;
+
etm->session = session;
etm->num_cpu = num_cpu;
--
2.34.1
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