[PATCH v6 15/18] perf tools: Minimal CALLCHAIN_DEFERRED support

Steven Rostedt
2025-04-25T14:56:16Z

From: Namhyung Kim <namhyung@kernel.org>

Add a new event type for deferred callchains and a new callback for the
struct perf_tool. For now it doesn't actually handle the deferred
callchains but it just marks the sample if it has the PERF_CONTEXT_
USER_DEFFERED in the callchain array.

At least, perf report can dump the raw data with this change. Actually
this requires the next commit to enable attr.defer_callchain, but if you
already have a data file, it'll show the following result.

$ perf report -D
...
0x5fe0@perf.data [0x40]: event: 22
.
. ... raw event: size 64 bytes
. 0000: 16 00 00 00 02 00 40 00 02 00 00 00 00 00 00 00 ......@.........
. 0010: 00 fe ff ff ff ff ff ff 4b d3 3f 25 45 7f 00 00 ........K.?%E...
. 0020: 21 03 00 00 21 03 00 00 43 02 12 ab 05 00 00 00 !...!...C.......
. 0030: 00 00 00 00 00 00 00 00 09 00 00 00 00 00 00 00 ................

0 24344920643 0x5fe0 [0x40]: PERF_RECORD_CALLCHAIN_DEFERRED(IP, 0x2): 801/801: 0
... FP chain: nr:2
..... 0: fffffffffffffe00
..... 1: 00007f45253fd34b
: unhandled!

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
tools/lib/perf/include/perf/event.h | 7 +++++++
tools/perf/util/event.c | 1 +
tools/perf/util/evsel.c | 15 +++++++++++++++
tools/perf/util/machine.c | 1 +
tools/perf/util/perf_event_attr_fprintf.c | 1 +
tools/perf/util/sample.h | 3 ++-
tools/perf/util/session.c | 17 +++++++++++++++++
tools/perf/util/tool.c | 1 +
tools/perf/util/tool.h | 3 ++-
9 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
index 37bb7771d914..f643a6a2b9fc 100644
--- a/tools/lib/perf/include/perf/event.h
+++ b/tools/lib/perf/include/perf/event.h
@@ -151,6 +151,12 @@ struct perf_record_switch {
__u32 next_prev_tid;
};

+struct perf_record_callchain_deferred {
+ struct perf_event_header header;
+ __u64 nr;
+ __u64 ips[];
+};
+
struct perf_record_header_attr {
struct perf_event_header header;
struct perf_event_attr attr;
@@ -494,6 +500,7 @@ union perf_event {
struct perf_record_read read;
struct perf_record_throttle throttle;
struct perf_record_sample sample;
+ struct perf_record_callchain_deferred callchain_deferred;
struct perf_record_bpf_event bpf;
struct perf_record_ksymbol ksymbol;
struct perf_record_text_poke_event text_poke;
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index c23b77f8f854..fec86519b7d4 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -58,6 +58,7 @@ static const char *perf_event__names[] = {
[PERF_RECORD_CGROUP] = "CGROUP",
[PERF_RECORD_TEXT_POKE] = "TEXT_POKE",
[PERF_RECORD_AUX_OUTPUT_HW_ID] = "AUX_OUTPUT_HW_ID",
+ [PERF_RECORD_CALLCHAIN_DEFERRED] = "CALLCHAIN_DEFERRED",
[PERF_RECORD_HEADER_ATTR] = "ATTR",
[PERF_RECORD_HEADER_EVENT_TYPE] = "EVENT_TYPE",
[PERF_RECORD_HEADER_TRACING_DATA] = "TRACING_DATA",
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 3c030da2e477..b872236a2413 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2948,6 +2948,18 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
data->data_src = PERF_MEM_DATA_SRC_NONE;
data->vcpu = -1;

+ if (event->header.type == PERF_RECORD_CALLCHAIN_DEFERRED) {
+ const u64 max_callchain_nr = UINT64_MAX / sizeof(u64);
+
+ data->callchain = (struct ip_callchain *)&event->callchain_deferred.nr;
+ if (data->callchain->nr > max_callchain_nr)
+ return -EFAULT;
+
+ if (evsel->core.attr.sample_id_all)
+ perf_evsel__parse_id_sample(evsel, event, data);
+ return 0;
+ }
+
if (event->header.type != PERF_RECORD_SAMPLE) {
if (!evsel->core.attr.sample_id_all)
return 0;
@@ -3078,6 +3090,9 @@ int evsel__parse_sample(struct evsel *evsel, union perf_event *event,
if (data->callchain->nr > max_callchain_nr)
return -EFAULT;
sz = data->callchain->nr * sizeof(u64);
+ if (evsel->core.attr.defer_callchain && data->callchain->nr >= 1 &&
+ data->callchain->ips[data->callchain->nr - 1] == PERF_CONTEXT_USER_DEFERRED)
+ data->deferred_callchain = true;
OVERFLOW_CHECK(array, sz, max_size);
array = (void *)array + sz;
}
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 2531b373f2cf..df76adce89ff 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -2089,6 +2089,7 @@ static int add_callchain_ip(struct thread *thread,
*cpumode = PERF_RECORD_MISC_KERNEL;
break;
case PERF_CONTEXT_USER:
+ case PERF_CONTEXT_USER_DEFERRED:
*cpumode = PERF_RECORD_MISC_USER;
break;
default:
diff --git a/tools/perf/util/perf_event_attr_fprintf.c b/tools/perf/util/perf_event_attr_fprintf.c
index 66b666d9ce64..abfd9b9a718c 100644
--- a/tools/perf/util/perf_event_attr_fprintf.c
+++ b/tools/perf/util/perf_event_attr_fprintf.c
@@ -343,6 +343,7 @@ int perf_event_attr__fprintf(FILE *fp, struct perf_event_attr *attr,
PRINT_ATTRf(inherit_thread, p_unsigned);
PRINT_ATTRf(remove_on_exec, p_unsigned);
PRINT_ATTRf(sigtrap, p_unsigned);
+ PRINT_ATTRf(defer_callchain, p_unsigned);

PRINT_ATTRn("{ wakeup_events, wakeup_watermark }", wakeup_events, p_unsigned, false);
PRINT_ATTRf(bp_type, p_unsigned);
diff --git a/tools/perf/util/sample.h b/tools/perf/util/sample.h
index 0e96240052e9..9d6e2f14551c 100644
--- a/tools/perf/util/sample.h
+++ b/tools/perf/util/sample.h
@@ -108,7 +108,8 @@ struct perf_sample {
u16 p_stage_cyc;
u16 retire_lat;
};
- bool no_hw_idx; /* No hw_idx collected in branch_stack */
+ bool no_hw_idx; /* No hw_idx collected in branch_stack */
+ bool deferred_callchain; /* Has deferred user callchains */
char insn[MAX_INSN];
void *raw_data;
struct ip_callchain *callchain;
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 60fb9997ea0d..30fb1d281be8 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -715,6 +715,7 @@ static perf_event__swap_op perf_event__swap_ops[] = {
[PERF_RECORD_CGROUP] = perf_event__cgroup_swap,
[PERF_RECORD_TEXT_POKE] = perf_event__text_poke_swap,
[PERF_RECORD_AUX_OUTPUT_HW_ID] = perf_event__all64_swap,
+ [PERF_RECORD_CALLCHAIN_DEFERRED] = perf_event__all64_swap,
[PERF_RECORD_HEADER_ATTR] = perf_event__hdr_attr_swap,
[PERF_RECORD_HEADER_EVENT_TYPE] = perf_event__event_type_swap,
[PERF_RECORD_HEADER_TRACING_DATA] = perf_event__tracing_data_swap,
@@ -1118,6 +1119,19 @@ static void dump_sample(struct evsel *evsel, union perf_event *event,
sample_read__printf(sample, evsel->core.attr.read_format);
}

+static void dump_deferred_callchain(struct evsel *evsel, union perf_event *event,
+ struct perf_sample *sample)
+{
+ if (!dump_trace)
+ return;
+
+ printf("(IP, 0x%x): %d/%d: %#" PRIx64 "\n",
+ event->header.misc, sample->pid, sample->tid, sample->ip);
+
+ if (evsel__has_callchain(evsel))
+ callchain__printf(evsel, sample);
+}
+
static void dump_read(struct evsel *evsel, union perf_event *event)
{
struct perf_record_read *read_event = &event->read;
@@ -1348,6 +1362,9 @@ static int machines__deliver_event(struct machines *machines,
return tool->text_poke(tool, event, sample, machine);
case PERF_RECORD_AUX_OUTPUT_HW_ID:
return tool->aux_output_hw_id(tool, event, sample, machine);
+ case PERF_RECORD_CALLCHAIN_DEFERRED:
+ dump_deferred_callchain(evsel, event, sample);
+ return tool->callchain_deferred(tool, event, sample, evsel, machine);
default:
++evlist->stats.nr_unknown_events;
return -1;
diff --git a/tools/perf/util/tool.c b/tools/perf/util/tool.c
index 3b7f390f26eb..e78f16de912e 100644
--- a/tools/perf/util/tool.c
+++ b/tools/perf/util/tool.c
@@ -259,6 +259,7 @@ void perf_tool__init(struct perf_tool *tool, bool ordered_events)
tool->read = process_event_sample_stub;
tool->throttle = process_event_stub;
tool->unthrottle = process_event_stub;
+ tool->callchain_deferred = process_event_sample_stub;
tool->attr = process_event_synth_attr_stub;
tool->event_update = process_event_synth_event_update_stub;
tool->tracing_data = process_event_synth_tracing_data_stub;
diff --git a/tools/perf/util/tool.h b/tools/perf/util/tool.h
index db1c7642b0d1..9987bbde6d5e 100644
--- a/tools/perf/util/tool.h
+++ b/tools/perf/util/tool.h
@@ -42,7 +42,8 @@ enum show_feature_header {

struct perf_tool {
event_sample sample,
- read;
+ read,
+ callchain_deferred;
event_op mmap,
mmap2,
comm,
--
2.47.2