Save samples with deferred callchains in a separate list and deliver
them after merging the user callchains. If users don't want to merge
they can set tool->merge_deferred_callchains to false to prevent the
behavior.
With previous result, now perf script will show the merged callchains.
$ perf script
...
pwd 2312 121.163435: 249113 cpu/cycles/P:
ffffffff845b78d8 __build_id_parse.isra.0+0x218 ([kernel.kallsyms])
ffffffff83bb5bf6 perf_event_mmap+0x2e6 ([kernel.kallsyms])
ffffffff83c31959 mprotect_fixup+0x1e9 ([kernel.kallsyms])
ffffffff83c31dc5 do_mprotect_pkey+0x2b5 ([kernel.kallsyms])
ffffffff83c3206f __x64_sys_mprotect+0x1f ([kernel.kallsyms])
ffffffff845e6692 do_syscall_64+0x62 ([kernel.kallsyms])
ffffffff8360012f entry_SYSCALL_64_after_hwframe+0x76 ([kernel.kallsyms])
7f18fe337fa7 mprotect+0x7 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
7f18fe330e0f _dl_sysdep_start+0x7f (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
7f18fe331448 _dl_start_user+0x0 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
...
The old output can be get using --no-merge-callchain option.
Also perf report can get the user callchain entry at the end.
$ perf report --no-children --stdio -q -S __build_id_parse.isra.0
# symbol: __build_id_parse.isra.0
8.40% pwd [kernel.kallsyms]
|
---__build_id_parse.isra.0
perf_event_mmap
mprotect_fixup
do_mprotect_pkey
__x64_sys_mprotect
do_syscall_64
entry_SYSCALL_64_after_hwframe
mprotect
_dl_sysdep_start
_dl_start_user
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/Documentation/perf-script.txt | 5 ++
tools/perf/builtin-inject.c | 1 +
tools/perf/builtin-report.c | 1 +
tools/perf/builtin-script.c | 4 ++
tools/perf/util/callchain.c | 29 +++++++++
tools/perf/util/callchain.h | 3 +
tools/perf/util/evlist.c | 1 +
tools/perf/util/evlist.h | 2 +
tools/perf/util/session.c | 79 +++++++++++++++++++++++-
tools/perf/util/tool.c | 2 +
tools/perf/util/tool.h | 1 +
11 files changed, 127 insertions(+), 1 deletion(-)
diff --git a/tools/perf/Documentation/perf-script.txt b/tools/perf/Documentation/perf-script.txt
index 28bec7e78bc858ba..03d1129606328d6d 100644
--- a/tools/perf/Documentation/perf-script.txt
+++ b/tools/perf/Documentation/perf-script.txt
@@ -527,6 +527,11 @@ include::itrace.txt[]
The known limitations include exception handing such as
setjmp/longjmp will have calls/returns not match.
+--merge-callchains::
+ Enable merging deferred user callchains if available. This is the
+ default behavior. If you want to see separate CALLCHAIN_DEFERRED
+ records for some reason, use --no-merge-callchains explicitly.
+
:GMEXAMPLECMD: script
:GMEXAMPLESUBCMD:
include::guest-files.txt[]
diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
index bd9245d2dd41aa48..51d2721b6db9dccb 100644
--- a/tools/perf/builtin-inject.c
+++ b/tools/perf/builtin-inject.c
@@ -2527,6 +2527,7 @@ int cmd_inject(int argc, const char **argv)
inject.tool.auxtrace = perf_event__repipe_auxtrace;
inject.tool.bpf_metadata = perf_event__repipe_op2_synth;
inject.tool.dont_split_sample_group = true;
+ inject.tool.merge_deferred_callchains = false;
inject.session = __perf_session__new(&data, &inject.tool,
/*trace_event_repipe=*/inject.output.is_pipe,
/*host_env=*/NULL);
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 2bc269f5fcef8023..add6b1c2aaf04270 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -1614,6 +1614,7 @@ int cmd_report(int argc, const char **argv)
report.tool.event_update = perf_event__process_event_update;
report.tool.feature = process_feature_event;
report.tool.ordering_requires_timestamps = true;
+ report.tool.merge_deferred_callchains = !dump_trace;
session = perf_session__new(&data, &report.tool);
if (IS_ERR(session)) {
diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 85b42205a71b3993..62e43d3c5ad731a0 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -4009,6 +4009,7 @@ int cmd_script(int argc, const char **argv)
bool header_only = false;
bool script_started = false;
bool unsorted_dump = false;
+ bool merge_deferred_callchains = true;
char *rec_script_path = NULL;
char *rep_script_path = NULL;
struct perf_session *session;
@@ -4162,6 +4163,8 @@ int cmd_script(int argc, const char **argv)
"Guest code can be found in hypervisor process"),
OPT_BOOLEAN('\0', "stitch-lbr", &script.stitch_lbr,
"Enable LBR callgraph stitching approach"),
+ OPT_BOOLEAN('\0', "merge-callchains", &merge_deferred_callchains,
+ "Enable merge deferred user callchains"),
OPTS_EVSWITCH(&script.evswitch),
OPT_END()
};
@@ -4418,6 +4421,7 @@ int cmd_script(int argc, const char **argv)
script.tool.throttle = process_throttle_event;
script.tool.unthrottle = process_throttle_event;
script.tool.ordering_requires_timestamps = true;
+ script.tool.merge_deferred_callchains = merge_deferred_callchains;
session = perf_session__new(&data, &script.tool);
if (IS_ERR(session))
return PTR_ERR(session);
diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index 2884187ccbbecfdc..71dc5a070065dd2a 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -1838,3 +1838,32 @@ int sample__for_each_callchain_node(struct thread *thread, struct evsel *evsel,
}
return 0;
}
+
+int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
+ struct perf_sample *sample_callchain)
+{
+ u64 nr_orig = sample_orig->callchain->nr - 1;
+ u64 nr_deferred = sample_callchain->callchain->nr;
+ struct ip_callchain *callchain;
+
+ if (sample_orig->callchain->nr < 2) {
+ sample_orig->deferred_callchain = false;
+ return -EINVAL;
+ }
+
+ callchain = calloc(1 + nr_orig + nr_deferred, sizeof(u64));
+ if (callchain == NULL) {
+ sample_orig->deferred_callchain = false;
+ return -ENOMEM;
+ }
+
+ callchain->nr = nr_orig + nr_deferred;
+ /* copy original including PERF_CONTEXT_USER_DEFERRED (but the cookie) */
+ memcpy(callchain->ips, sample_orig->callchain->ips, nr_orig * sizeof(u64));
+ /* copy deferred user callchains */
+ memcpy(&callchain->ips[nr_orig], sample_callchain->callchain->ips,
+ nr_deferred * sizeof(u64));
+
+ sample_orig->callchain = callchain;
+ return 0;
+}
diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
index d5ae4fbb7ce5fa44..2a52af8c80ace33c 100644
--- a/tools/perf/util/callchain.h
+++ b/tools/perf/util/callchain.h
@@ -318,4 +318,7 @@ int sample__for_each_callchain_node(struct thread *thread, struct evsel *evsel,
struct perf_sample *sample, int max_stack,
bool symbols, callchain_iter_fn cb, void *data);
+int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
+ struct perf_sample *sample_callchain);
+
#endif /* __PERF_CALLCHAIN_H */
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index e8217efdda5323c6..03674d2cbd015e4f 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -85,6 +85,7 @@ void evlist__init(struct evlist *evlist, struct perf_cpu_map *cpus,
evlist->ctl_fd.pos = -1;
evlist->nr_br_cntr = -1;
metricgroup__rblist_init(&evlist->metric_events);
+ INIT_LIST_HEAD(&evlist->deferred_samples);
}
struct evlist *evlist__new(void)
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 5e71e3dc60423079..911834ae7c2a6f76 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -92,6 +92,8 @@ struct evlist {
* of struct metric_expr.
*/
struct rblist metric_events;
+ /* samples with deferred_callchain would wait here. */
+ struct list_head deferred_samples;
};
struct evsel_str_handler {
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 361e15c1f26a96d0..dc570ad47ccc2c63 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1285,6 +1285,66 @@ static int evlist__deliver_sample(struct evlist *evlist, const struct perf_tool
per_thread);
}
+/*
+ * Samples with deferred callchains should wait for the next matching
+ * PERF_RECORD_CALLCHAIN_RECORD entries. Keep the events in a list and
+ * deliver them once it finds the callchains.
+ */
+struct deferred_event {
+ struct list_head list;
+ union perf_event *event;
+};
+
+static int evlist__deliver_deferred_callchain(struct evlist *evlist,
+ const struct perf_tool *tool,
+ union perf_event *event,
+ struct perf_sample *sample,
+ struct machine *machine)
+{
+ struct deferred_event *de, *tmp;
+ struct evsel *evsel;
+ int ret = 0;
+
+ if (!tool->merge_deferred_callchains) {
+ evsel = evlist__id2evsel(evlist, sample->id);
+ return tool->callchain_deferred(tool, event, sample,
+ evsel, machine);
+ }
+
+ list_for_each_entry_safe(de, tmp, &evlist->deferred_samples, list) {
+ struct perf_sample orig_sample;
+
+ ret = evlist__parse_sample(evlist, de->event, &orig_sample);
+ if (ret < 0) {
+ pr_err("failed to parse original sample\n");
+ break;
+ }
+
+ if (sample->tid != orig_sample.tid)
+ continue;
+
+ if (event->callchain_deferred.cookie == orig_sample.deferred_cookie)
+ sample__merge_deferred_callchain(&orig_sample, sample);
+ else
+ orig_sample.deferred_callchain = false;
+
+ evsel = evlist__id2evsel(evlist, orig_sample.id);
+ ret = evlist__deliver_sample(evlist, tool, de->event,
+ &orig_sample, evsel, machine);
+
+ if (orig_sample.deferred_callchain)
+ free(orig_sample.callchain);
+
+ list_del(&de->list);
+ free(de->event);
+ free(de);
+
+ if (ret)
+ break;
+ }
+ return ret;
+}
+
static int machines__deliver_event(struct machines *machines,
struct evlist *evlist,
union perf_event *event,
@@ -1313,6 +1373,22 @@ static int machines__deliver_event(struct machines *machines,
return 0;
}
dump_sample(evsel, event, sample, perf_env__arch(machine->env));
+ if (sample->deferred_callchain && tool->merge_deferred_callchains) {
+ struct deferred_event *de = malloc(sizeof(*de));
+ size_t sz = event->header.size;
+
+ if (de == NULL)
+ return -ENOMEM;
+
+ de->event = malloc(sz);
+ if (de->event == NULL) {
+ free(de);
+ return -ENOMEM;
+ }
+ memcpy(de->event, event, sz);
+ list_add_tail(&de->list, &evlist->deferred_samples);
+ return 0;
+ }
return evlist__deliver_sample(evlist, tool, event, sample, evsel, machine);
case PERF_RECORD_MMAP:
return tool->mmap(tool, event, sample, machine);
@@ -1372,7 +1448,8 @@ static int machines__deliver_event(struct machines *machines,
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);
+ return evlist__deliver_deferred_callchain(evlist, tool, event,
+ sample, machine);
default:
++evlist->stats.nr_unknown_events;
return -1;
diff --git a/tools/perf/util/tool.c b/tools/perf/util/tool.c
index e77f0e2ecc1f79db..27ba5849c74a2e7d 100644
--- a/tools/perf/util/tool.c
+++ b/tools/perf/util/tool.c
@@ -266,6 +266,7 @@ void perf_tool__init(struct perf_tool *tool, bool ordered_events)
tool->cgroup_events = false;
tool->no_warn = false;
tool->show_feat_hdr = SHOW_FEAT_NO_HEADER;
+ tool->merge_deferred_callchains = true;
tool->sample = process_event_sample_stub;
tool->mmap = process_event_stub;
@@ -448,6 +449,7 @@ void delegate_tool__init(struct delegate_tool *tool, struct perf_tool *delegate)
tool->tool.cgroup_events = delegate->cgroup_events;
tool->tool.no_warn = delegate->no_warn;
tool->tool.show_feat_hdr = delegate->show_feat_hdr;
+ tool->tool.merge_deferred_callchains = delegate->merge_deferred_callchains;
tool->tool.sample = delegate_sample;
tool->tool.read = delegate_read;
diff --git a/tools/perf/util/tool.h b/tools/perf/util/tool.h
index 9b9f0a8cbf3de4b5..e96b69d25a5b737d 100644
--- a/tools/perf/util/tool.h
+++ b/tools/perf/util/tool.h
@@ -90,6 +90,7 @@ struct perf_tool {
bool cgroup_events;
bool no_warn;
bool dont_split_sample_group;
+ bool merge_deferred_callchains;
enum show_feature_header show_feat_hdr;
};
--
2.52.0.rc2.455.g230fcf2819-googHello Namhyung!
On 11/21/2025 12:48 AM, Namhyung Kim wrote:
> Save samples with deferred callchains in a separate list and deliver
> them after merging the user callchains. If users don't want to merge
> they can set tool->merge_deferred_callchains to false to prevent the
> behavior.
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> +int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
> + struct perf_sample *sample_callchain)
> +{
> + u64 nr_orig = sample_orig->callchain->nr - 1;
> + u64 nr_deferred = sample_callchain->callchain->nr;
> + struct ip_callchain *callchain;
> +
> + if (sample_orig->callchain->nr < 2) {
> + sample_orig->deferred_callchain = false;
> + return -EINVAL;
> + }
> +
> + callchain = calloc(1 + nr_orig + nr_deferred, sizeof(u64));
> + if (callchain == NULL) {
> + sample_orig->deferred_callchain = false;
> + return -ENOMEM;
> + }
> +
> + callchain->nr = nr_orig + nr_deferred;
> + /* copy original including PERF_CONTEXT_USER_DEFERRED (but the cookie) */
> + memcpy(callchain->ips, sample_orig->callchain->ips, nr_orig * sizeof(u64));
> + /* copy deferred user callchains */
> + memcpy(&callchain->ips[nr_orig], sample_callchain->callchain->ips,
> + nr_deferred * sizeof(u64));
> +
> + sample_orig->callchain = callchain;
Hope you don't mind my naive question, as I don't have a clue about perf:
Doesn't the sample_orig->callchain storage need to be free'd prior to
assigning the newly allocated one? Or is that just part of a large
block that got allocated in one piece? How is then the one allocated
here ever free'd?
> + return 0;
> +}
Thanks and regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com
IBM
IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Böblingen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/
Hello Namhyung,
sorry for the fuss!
On 12/12/2025 12:16 PM, Jens Remus wrote:
> On 11/21/2025 12:48 AM, Namhyung Kim wrote:
>> Save samples with deferred callchains in a separate list and deliver
>> them after merging the user callchains. If users don't want to merge
>> they can set tool->merge_deferred_callchains to false to prevent the
>> behavior.
>
>> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
>
>> +int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
>> + struct perf_sample *sample_callchain)
>> +{
>> + u64 nr_orig = sample_orig->callchain->nr - 1;
>> + u64 nr_deferred = sample_callchain->callchain->nr;
>> + struct ip_callchain *callchain;
>> +
>> + if (sample_orig->callchain->nr < 2) {
>> + sample_orig->deferred_callchain = false;
>> + return -EINVAL;
>> + }
>> +
>> + callchain = calloc(1 + nr_orig + nr_deferred, sizeof(u64));
>> + if (callchain == NULL) {
>> + sample_orig->deferred_callchain = false;
>> + return -ENOMEM;
>> + }
>> +
>> + callchain->nr = nr_orig + nr_deferred;
>> + /* copy original including PERF_CONTEXT_USER_DEFERRED (but the cookie) */
>> + memcpy(callchain->ips, sample_orig->callchain->ips, nr_orig * sizeof(u64));
>> + /* copy deferred user callchains */
>> + memcpy(&callchain->ips[nr_orig], sample_callchain->callchain->ips,
>> + nr_deferred * sizeof(u64));
>> +
>> + sample_orig->callchain = callchain;
>
> Hope you don't mind my naive question, as I don't have a clue about perf:
>
> Doesn't the sample_orig->callchain storage need to be free'd prior to
> assigning the newly allocated one? Or is that just part of a large
> block that got allocated in one piece? How is then the one allocated
> here ever free'd?
Never mind, I found that it is getting free'd in
evlist__deliver_deferred_callchain().
>
>> + return 0;
>> +}
> Thanks and regards,
> Jens
Regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com
IBM
IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Böblingen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/
On Thu, Nov 20, 2025 at 3:48 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> Save samples with deferred callchains in a separate list and deliver
> them after merging the user callchains. If users don't want to merge
> they can set tool->merge_deferred_callchains to false to prevent the
> behavior.
>
> With previous result, now perf script will show the merged callchains.
>
> $ perf script
> ...
> pwd 2312 121.163435: 249113 cpu/cycles/P:
> ffffffff845b78d8 __build_id_parse.isra.0+0x218 ([kernel.kallsyms])
> ffffffff83bb5bf6 perf_event_mmap+0x2e6 ([kernel.kallsyms])
> ffffffff83c31959 mprotect_fixup+0x1e9 ([kernel.kallsyms])
> ffffffff83c31dc5 do_mprotect_pkey+0x2b5 ([kernel.kallsyms])
> ffffffff83c3206f __x64_sys_mprotect+0x1f ([kernel.kallsyms])
> ffffffff845e6692 do_syscall_64+0x62 ([kernel.kallsyms])
> ffffffff8360012f entry_SYSCALL_64_after_hwframe+0x76 ([kernel.kallsyms])
> 7f18fe337fa7 mprotect+0x7 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
> 7f18fe330e0f _dl_sysdep_start+0x7f (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
> 7f18fe331448 _dl_start_user+0x0 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
> ...
>
> The old output can be get using --no-merge-callchain option.
> Also perf report can get the user callchain entry at the end.
>
> $ perf report --no-children --stdio -q -S __build_id_parse.isra.0
> # symbol: __build_id_parse.isra.0
> 8.40% pwd [kernel.kallsyms]
> |
> ---__build_id_parse.isra.0
> perf_event_mmap
> mprotect_fixup
> do_mprotect_pkey
> __x64_sys_mprotect
> do_syscall_64
> entry_SYSCALL_64_after_hwframe
> mprotect
> _dl_sysdep_start
> _dl_start_user
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/Documentation/perf-script.txt | 5 ++
> tools/perf/builtin-inject.c | 1 +
> tools/perf/builtin-report.c | 1 +
> tools/perf/builtin-script.c | 4 ++
> tools/perf/util/callchain.c | 29 +++++++++
> tools/perf/util/callchain.h | 3 +
> tools/perf/util/evlist.c | 1 +
> tools/perf/util/evlist.h | 2 +
> tools/perf/util/session.c | 79 +++++++++++++++++++++++-
> tools/perf/util/tool.c | 2 +
> tools/perf/util/tool.h | 1 +
> 11 files changed, 127 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Documentation/perf-script.txt b/tools/perf/Documentation/perf-script.txt
> index 28bec7e78bc858ba..03d1129606328d6d 100644
> --- a/tools/perf/Documentation/perf-script.txt
> +++ b/tools/perf/Documentation/perf-script.txt
> @@ -527,6 +527,11 @@ include::itrace.txt[]
> The known limitations include exception handing such as
> setjmp/longjmp will have calls/returns not match.
>
> +--merge-callchains::
> + Enable merging deferred user callchains if available. This is the
> + default behavior. If you want to see separate CALLCHAIN_DEFERRED
> + records for some reason, use --no-merge-callchains explicitly.
> +
> :GMEXAMPLECMD: script
> :GMEXAMPLESUBCMD:
> include::guest-files.txt[]
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index bd9245d2dd41aa48..51d2721b6db9dccb 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/tools/perf/builtin-inject.c
> @@ -2527,6 +2527,7 @@ int cmd_inject(int argc, const char **argv)
> inject.tool.auxtrace = perf_event__repipe_auxtrace;
> inject.tool.bpf_metadata = perf_event__repipe_op2_synth;
> inject.tool.dont_split_sample_group = true;
> + inject.tool.merge_deferred_callchains = false;
> inject.session = __perf_session__new(&data, &inject.tool,
> /*trace_event_repipe=*/inject.output.is_pipe,
> /*host_env=*/NULL);
> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> index 2bc269f5fcef8023..add6b1c2aaf04270 100644
> --- a/tools/perf/builtin-report.c
> +++ b/tools/perf/builtin-report.c
> @@ -1614,6 +1614,7 @@ int cmd_report(int argc, const char **argv)
> report.tool.event_update = perf_event__process_event_update;
> report.tool.feature = process_feature_event;
> report.tool.ordering_requires_timestamps = true;
> + report.tool.merge_deferred_callchains = !dump_trace;
>
> session = perf_session__new(&data, &report.tool);
> if (IS_ERR(session)) {
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index 85b42205a71b3993..62e43d3c5ad731a0 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -4009,6 +4009,7 @@ int cmd_script(int argc, const char **argv)
> bool header_only = false;
> bool script_started = false;
> bool unsorted_dump = false;
> + bool merge_deferred_callchains = true;
> char *rec_script_path = NULL;
> char *rep_script_path = NULL;
> struct perf_session *session;
> @@ -4162,6 +4163,8 @@ int cmd_script(int argc, const char **argv)
> "Guest code can be found in hypervisor process"),
> OPT_BOOLEAN('\0', "stitch-lbr", &script.stitch_lbr,
> "Enable LBR callgraph stitching approach"),
> + OPT_BOOLEAN('\0', "merge-callchains", &merge_deferred_callchains,
> + "Enable merge deferred user callchains"),
> OPTS_EVSWITCH(&script.evswitch),
> OPT_END()
> };
> @@ -4418,6 +4421,7 @@ int cmd_script(int argc, const char **argv)
> script.tool.throttle = process_throttle_event;
> script.tool.unthrottle = process_throttle_event;
> script.tool.ordering_requires_timestamps = true;
> + script.tool.merge_deferred_callchains = merge_deferred_callchains;
> session = perf_session__new(&data, &script.tool);
> if (IS_ERR(session))
> return PTR_ERR(session);
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> index 2884187ccbbecfdc..71dc5a070065dd2a 100644
> --- a/tools/perf/util/callchain.c
> +++ b/tools/perf/util/callchain.c
> @@ -1838,3 +1838,32 @@ int sample__for_each_callchain_node(struct thread *thread, struct evsel *evsel,
> }
> return 0;
> }
> +
> +int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
nit: We use the term deferred rather than original except in this
context. I think deferred is a little more intention revealing than
original. Perhaps add a comment capturing that the original sample is
the deferred kernel sample.
Thanks,
Ian
> + struct perf_sample *sample_callchain)
> +{
> + u64 nr_orig = sample_orig->callchain->nr - 1;
> + u64 nr_deferred = sample_callchain->callchain->nr;
> + struct ip_callchain *callchain;
> +
> + if (sample_orig->callchain->nr < 2) {
> + sample_orig->deferred_callchain = false;
> + return -EINVAL;
> + }
> +
> + callchain = calloc(1 + nr_orig + nr_deferred, sizeof(u64));
> + if (callchain == NULL) {
> + sample_orig->deferred_callchain = false;
> + return -ENOMEM;
> + }
> +
> + callchain->nr = nr_orig + nr_deferred;
> + /* copy original including PERF_CONTEXT_USER_DEFERRED (but the cookie) */
> + memcpy(callchain->ips, sample_orig->callchain->ips, nr_orig * sizeof(u64));
> + /* copy deferred user callchains */
> + memcpy(&callchain->ips[nr_orig], sample_callchain->callchain->ips,
> + nr_deferred * sizeof(u64));
> +
> + sample_orig->callchain = callchain;
> + return 0;
> +}
> diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
> index d5ae4fbb7ce5fa44..2a52af8c80ace33c 100644
> --- a/tools/perf/util/callchain.h
> +++ b/tools/perf/util/callchain.h
> @@ -318,4 +318,7 @@ int sample__for_each_callchain_node(struct thread *thread, struct evsel *evsel,
> struct perf_sample *sample, int max_stack,
> bool symbols, callchain_iter_fn cb, void *data);
>
> +int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
> + struct perf_sample *sample_callchain);
> +
> #endif /* __PERF_CALLCHAIN_H */
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index e8217efdda5323c6..03674d2cbd015e4f 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -85,6 +85,7 @@ void evlist__init(struct evlist *evlist, struct perf_cpu_map *cpus,
> evlist->ctl_fd.pos = -1;
> evlist->nr_br_cntr = -1;
> metricgroup__rblist_init(&evlist->metric_events);
> + INIT_LIST_HEAD(&evlist->deferred_samples);
> }
>
> struct evlist *evlist__new(void)
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 5e71e3dc60423079..911834ae7c2a6f76 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -92,6 +92,8 @@ struct evlist {
> * of struct metric_expr.
> */
> struct rblist metric_events;
> + /* samples with deferred_callchain would wait here. */
> + struct list_head deferred_samples;
> };
>
> struct evsel_str_handler {
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 361e15c1f26a96d0..dc570ad47ccc2c63 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1285,6 +1285,66 @@ static int evlist__deliver_sample(struct evlist *evlist, const struct perf_tool
> per_thread);
> }
>
> +/*
> + * Samples with deferred callchains should wait for the next matching
> + * PERF_RECORD_CALLCHAIN_RECORD entries. Keep the events in a list and
> + * deliver them once it finds the callchains.
> + */
> +struct deferred_event {
> + struct list_head list;
> + union perf_event *event;
> +};
> +
> +static int evlist__deliver_deferred_callchain(struct evlist *evlist,
> + const struct perf_tool *tool,
> + union perf_event *event,
> + struct perf_sample *sample,
> + struct machine *machine)
> +{
> + struct deferred_event *de, *tmp;
> + struct evsel *evsel;
> + int ret = 0;
> +
> + if (!tool->merge_deferred_callchains) {
> + evsel = evlist__id2evsel(evlist, sample->id);
> + return tool->callchain_deferred(tool, event, sample,
> + evsel, machine);
> + }
> +
> + list_for_each_entry_safe(de, tmp, &evlist->deferred_samples, list) {
> + struct perf_sample orig_sample;
> +
> + ret = evlist__parse_sample(evlist, de->event, &orig_sample);
> + if (ret < 0) {
> + pr_err("failed to parse original sample\n");
> + break;
> + }
> +
> + if (sample->tid != orig_sample.tid)
> + continue;
> +
> + if (event->callchain_deferred.cookie == orig_sample.deferred_cookie)
> + sample__merge_deferred_callchain(&orig_sample, sample);
> + else
> + orig_sample.deferred_callchain = false;
> +
> + evsel = evlist__id2evsel(evlist, orig_sample.id);
> + ret = evlist__deliver_sample(evlist, tool, de->event,
> + &orig_sample, evsel, machine);
> +
> + if (orig_sample.deferred_callchain)
> + free(orig_sample.callchain);
> +
> + list_del(&de->list);
> + free(de->event);
> + free(de);
> +
> + if (ret)
> + break;
> + }
> + return ret;
> +}
> +
> static int machines__deliver_event(struct machines *machines,
> struct evlist *evlist,
> union perf_event *event,
> @@ -1313,6 +1373,22 @@ static int machines__deliver_event(struct machines *machines,
> return 0;
> }
> dump_sample(evsel, event, sample, perf_env__arch(machine->env));
> + if (sample->deferred_callchain && tool->merge_deferred_callchains) {
> + struct deferred_event *de = malloc(sizeof(*de));
> + size_t sz = event->header.size;
> +
> + if (de == NULL)
> + return -ENOMEM;
> +
> + de->event = malloc(sz);
> + if (de->event == NULL) {
> + free(de);
> + return -ENOMEM;
> + }
> + memcpy(de->event, event, sz);
> + list_add_tail(&de->list, &evlist->deferred_samples);
> + return 0;
> + }
> return evlist__deliver_sample(evlist, tool, event, sample, evsel, machine);
> case PERF_RECORD_MMAP:
> return tool->mmap(tool, event, sample, machine);
> @@ -1372,7 +1448,8 @@ static int machines__deliver_event(struct machines *machines,
> 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);
> + return evlist__deliver_deferred_callchain(evlist, tool, event,
> + sample, machine);
> default:
> ++evlist->stats.nr_unknown_events;
> return -1;
> diff --git a/tools/perf/util/tool.c b/tools/perf/util/tool.c
> index e77f0e2ecc1f79db..27ba5849c74a2e7d 100644
> --- a/tools/perf/util/tool.c
> +++ b/tools/perf/util/tool.c
> @@ -266,6 +266,7 @@ void perf_tool__init(struct perf_tool *tool, bool ordered_events)
> tool->cgroup_events = false;
> tool->no_warn = false;
> tool->show_feat_hdr = SHOW_FEAT_NO_HEADER;
> + tool->merge_deferred_callchains = true;
>
> tool->sample = process_event_sample_stub;
> tool->mmap = process_event_stub;
> @@ -448,6 +449,7 @@ void delegate_tool__init(struct delegate_tool *tool, struct perf_tool *delegate)
> tool->tool.cgroup_events = delegate->cgroup_events;
> tool->tool.no_warn = delegate->no_warn;
> tool->tool.show_feat_hdr = delegate->show_feat_hdr;
> + tool->tool.merge_deferred_callchains = delegate->merge_deferred_callchains;
>
> tool->tool.sample = delegate_sample;
> tool->tool.read = delegate_read;
> diff --git a/tools/perf/util/tool.h b/tools/perf/util/tool.h
> index 9b9f0a8cbf3de4b5..e96b69d25a5b737d 100644
> --- a/tools/perf/util/tool.h
> +++ b/tools/perf/util/tool.h
> @@ -90,6 +90,7 @@ struct perf_tool {
> bool cgroup_events;
> bool no_warn;
> bool dont_split_sample_group;
> + bool merge_deferred_callchains;
> enum show_feature_header show_feat_hdr;
> };
>
> --
> 2.52.0.rc2.455.g230fcf2819-goog
>
On Tue, Dec 02, 2025 at 03:14:31PM -0800, Ian Rogers wrote:
> On Thu, Nov 20, 2025 at 3:48 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > Save samples with deferred callchains in a separate list and deliver
> > them after merging the user callchains. If users don't want to merge
> > they can set tool->merge_deferred_callchains to false to prevent the
> > behavior.
> >
> > With previous result, now perf script will show the merged callchains.
> >
> > $ perf script
> > ...
> > pwd 2312 121.163435: 249113 cpu/cycles/P:
> > ffffffff845b78d8 __build_id_parse.isra.0+0x218 ([kernel.kallsyms])
> > ffffffff83bb5bf6 perf_event_mmap+0x2e6 ([kernel.kallsyms])
> > ffffffff83c31959 mprotect_fixup+0x1e9 ([kernel.kallsyms])
> > ffffffff83c31dc5 do_mprotect_pkey+0x2b5 ([kernel.kallsyms])
> > ffffffff83c3206f __x64_sys_mprotect+0x1f ([kernel.kallsyms])
> > ffffffff845e6692 do_syscall_64+0x62 ([kernel.kallsyms])
> > ffffffff8360012f entry_SYSCALL_64_after_hwframe+0x76 ([kernel.kallsyms])
> > 7f18fe337fa7 mprotect+0x7 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
> > 7f18fe330e0f _dl_sysdep_start+0x7f (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
> > 7f18fe331448 _dl_start_user+0x0 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
> > ...
> >
> > The old output can be get using --no-merge-callchain option.
> > Also perf report can get the user callchain entry at the end.
> >
> > $ perf report --no-children --stdio -q -S __build_id_parse.isra.0
> > # symbol: __build_id_parse.isra.0
> > 8.40% pwd [kernel.kallsyms]
> > |
> > ---__build_id_parse.isra.0
> > perf_event_mmap
> > mprotect_fixup
> > do_mprotect_pkey
> > __x64_sys_mprotect
> > do_syscall_64
> > entry_SYSCALL_64_after_hwframe
> > mprotect
> > _dl_sysdep_start
> > _dl_start_user
> >
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
>
> Reviewed-by: Ian Rogers <irogers@google.com>
>
> > ---
> > tools/perf/Documentation/perf-script.txt | 5 ++
> > tools/perf/builtin-inject.c | 1 +
> > tools/perf/builtin-report.c | 1 +
> > tools/perf/builtin-script.c | 4 ++
> > tools/perf/util/callchain.c | 29 +++++++++
> > tools/perf/util/callchain.h | 3 +
> > tools/perf/util/evlist.c | 1 +
> > tools/perf/util/evlist.h | 2 +
> > tools/perf/util/session.c | 79 +++++++++++++++++++++++-
> > tools/perf/util/tool.c | 2 +
> > tools/perf/util/tool.h | 1 +
> > 11 files changed, 127 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/Documentation/perf-script.txt b/tools/perf/Documentation/perf-script.txt
> > index 28bec7e78bc858ba..03d1129606328d6d 100644
> > --- a/tools/perf/Documentation/perf-script.txt
> > +++ b/tools/perf/Documentation/perf-script.txt
> > @@ -527,6 +527,11 @@ include::itrace.txt[]
> > The known limitations include exception handing such as
> > setjmp/longjmp will have calls/returns not match.
> >
> > +--merge-callchains::
> > + Enable merging deferred user callchains if available. This is the
> > + default behavior. If you want to see separate CALLCHAIN_DEFERRED
> > + records for some reason, use --no-merge-callchains explicitly.
> > +
> > :GMEXAMPLECMD: script
> > :GMEXAMPLESUBCMD:
> > include::guest-files.txt[]
> > diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> > index bd9245d2dd41aa48..51d2721b6db9dccb 100644
> > --- a/tools/perf/builtin-inject.c
> > +++ b/tools/perf/builtin-inject.c
> > @@ -2527,6 +2527,7 @@ int cmd_inject(int argc, const char **argv)
> > inject.tool.auxtrace = perf_event__repipe_auxtrace;
> > inject.tool.bpf_metadata = perf_event__repipe_op2_synth;
> > inject.tool.dont_split_sample_group = true;
> > + inject.tool.merge_deferred_callchains = false;
> > inject.session = __perf_session__new(&data, &inject.tool,
> > /*trace_event_repipe=*/inject.output.is_pipe,
> > /*host_env=*/NULL);
> > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > index 2bc269f5fcef8023..add6b1c2aaf04270 100644
> > --- a/tools/perf/builtin-report.c
> > +++ b/tools/perf/builtin-report.c
> > @@ -1614,6 +1614,7 @@ int cmd_report(int argc, const char **argv)
> > report.tool.event_update = perf_event__process_event_update;
> > report.tool.feature = process_feature_event;
> > report.tool.ordering_requires_timestamps = true;
> > + report.tool.merge_deferred_callchains = !dump_trace;
> >
> > session = perf_session__new(&data, &report.tool);
> > if (IS_ERR(session)) {
> > diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> > index 85b42205a71b3993..62e43d3c5ad731a0 100644
> > --- a/tools/perf/builtin-script.c
> > +++ b/tools/perf/builtin-script.c
> > @@ -4009,6 +4009,7 @@ int cmd_script(int argc, const char **argv)
> > bool header_only = false;
> > bool script_started = false;
> > bool unsorted_dump = false;
> > + bool merge_deferred_callchains = true;
> > char *rec_script_path = NULL;
> > char *rep_script_path = NULL;
> > struct perf_session *session;
> > @@ -4162,6 +4163,8 @@ int cmd_script(int argc, const char **argv)
> > "Guest code can be found in hypervisor process"),
> > OPT_BOOLEAN('\0', "stitch-lbr", &script.stitch_lbr,
> > "Enable LBR callgraph stitching approach"),
> > + OPT_BOOLEAN('\0', "merge-callchains", &merge_deferred_callchains,
> > + "Enable merge deferred user callchains"),
> > OPTS_EVSWITCH(&script.evswitch),
> > OPT_END()
> > };
> > @@ -4418,6 +4421,7 @@ int cmd_script(int argc, const char **argv)
> > script.tool.throttle = process_throttle_event;
> > script.tool.unthrottle = process_throttle_event;
> > script.tool.ordering_requires_timestamps = true;
> > + script.tool.merge_deferred_callchains = merge_deferred_callchains;
> > session = perf_session__new(&data, &script.tool);
> > if (IS_ERR(session))
> > return PTR_ERR(session);
> > diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> > index 2884187ccbbecfdc..71dc5a070065dd2a 100644
> > --- a/tools/perf/util/callchain.c
> > +++ b/tools/perf/util/callchain.c
> > @@ -1838,3 +1838,32 @@ int sample__for_each_callchain_node(struct thread *thread, struct evsel *evsel,
> > }
> > return 0;
> > }
> > +
> > +int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
>
> nit: We use the term deferred rather than original except in this
> context. I think deferred is a little more intention revealing than
> original. Perhaps add a comment capturing that the original sample is
> the deferred kernel sample.
Sure, will add.
Thanks,
Namhyung
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