Re: [PATCH v3 3/3] perf evlist: Improve default event for s390

[Thomas Richter <tmricht@linux.ibm.com>]

On 3/13/26 21:28, Ian Rogers wrote:
> Frame pointer callchains are not supported on s390 and dwarf
> callchains are only supported on software events.
> 
> Switch the default event from cycles to cpu-clock or task-clock on
> s390 if callchains are enabled.
> 
> If frame pointer callchains are requested on s390, warn and switch to
> dwarf callchains.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/builtin-record.c      |  3 ++-
>  tools/perf/builtin-top.c         |  2 +-
>  tools/perf/tests/event_update.c  |  4 +++-
>  tools/perf/tests/expand-cgroup.c |  4 +++-
>  tools/perf/tests/perf-record.c   |  7 ++++--
>  tools/perf/tests/topology.c      |  4 +++-
>  tools/perf/util/evlist.c         | 37 +++++++++++++++++++-------------
>  tools/perf/util/evlist.h         |  2 +-
>  tools/perf/util/evsel.c          | 11 ++++++++--
>  9 files changed, 49 insertions(+), 25 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 60d764068302..07ecc8a5fec7 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -4310,7 +4310,8 @@ int cmd_record(int argc, const char **argv)
>  		record.opts.tail_synthesize = true;
>  
>  	if (rec->evlist->core.nr_entries == 0) {
> -		struct evlist *def_evlist = evlist__new_default();
> +		struct evlist *def_evlist = evlist__new_default(&rec->opts.target,
> +								callchain_param.enabled);
>  
>  		if (!def_evlist)
>  			goto out;
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index 710604c4f6f6..58bab595b024 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -1695,7 +1695,7 @@ int cmd_top(int argc, const char **argv)
>  		goto out_delete_evlist;
>  
>  	if (!top.evlist->core.nr_entries) {
> -		struct evlist *def_evlist = evlist__new_default();
> +		struct evlist *def_evlist = evlist__new_default(target, callchain_param.enabled);
>  
>  		if (!def_evlist)
>  			goto out_delete_evlist;
> diff --git a/tools/perf/tests/event_update.c b/tools/perf/tests/event_update.c
> index cb9e6de2e033..facc65e29f20 100644
> --- a/tools/perf/tests/event_update.c
> +++ b/tools/perf/tests/event_update.c
> @@ -8,6 +8,7 @@
>  #include "header.h"
>  #include "machine.h"
>  #include "util/synthetic-events.h"
> +#include "target.h"
>  #include "tool.h"
>  #include "tests.h"
>  #include "debug.h"
> @@ -81,7 +82,8 @@ static int test__event_update(struct test_suite *test __maybe_unused, int subtes
>  {
>  	struct evsel *evsel;
>  	struct event_name tmp;
> -	struct evlist *evlist = evlist__new_default();
> +	struct target target = {};
> +	struct evlist *evlist = evlist__new_default(&target, /*sample_callchains=*/false);
>  
>  	TEST_ASSERT_VAL("failed to get evlist", evlist);
>  
> diff --git a/tools/perf/tests/expand-cgroup.c b/tools/perf/tests/expand-cgroup.c
> index c7b32a220ca1..dd547f2f77cc 100644
> --- a/tools/perf/tests/expand-cgroup.c
> +++ b/tools/perf/tests/expand-cgroup.c
> @@ -8,6 +8,7 @@
>  #include "parse-events.h"
>  #include "pmu-events/pmu-events.h"
>  #include "pfm.h"
> +#include "target.h"
>  #include <subcmd/parse-options.h>
>  #include <stdio.h>
>  #include <stdlib.h>
> @@ -99,7 +100,8 @@ out:	for (i = 0; i < nr_events; i++)
>  static int expand_default_events(void)
>  {
>  	int ret;
> -	struct evlist *evlist = evlist__new_default();
> +	struct target target = {};
> +	struct evlist *evlist = evlist__new_default(&target, /*sample_callchains=*/false);
>  
>  	TEST_ASSERT_VAL("failed to get evlist", evlist);
>  
> diff --git a/tools/perf/tests/perf-record.c b/tools/perf/tests/perf-record.c
> index efbd9cd60c63..c6e31ab8a6b8 100644
> --- a/tools/perf/tests/perf-record.c
> +++ b/tools/perf/tests/perf-record.c
> @@ -84,8 +84,11 @@ static int test__PERF_RECORD(struct test_suite *test __maybe_unused, int subtest
>  	CPU_ZERO_S(cpu_mask_size, cpu_mask);
>  
>  	perf_sample__init(&sample, /*all=*/false);
> -	if (evlist == NULL) /* Fallback for kernels lacking PERF_COUNT_SW_DUMMY */
> -		evlist = evlist__new_default();
> +	if (evlist == NULL) { /* Fallback for kernels lacking PERF_COUNT_SW_DUMMY */
> +		struct target target = {};
> +
> +		evlist = evlist__new_default(&target, /*sample_callchains=*/false);
> +	}
>  
>  	if (evlist == NULL) {
>  		pr_debug("Not enough memory to create evlist\n");
> diff --git a/tools/perf/tests/topology.c b/tools/perf/tests/topology.c
> index ec01150d208d..a34a7ab19a80 100644
> --- a/tools/perf/tests/topology.c
> +++ b/tools/perf/tests/topology.c
> @@ -9,6 +9,7 @@
>  #include "evlist.h"
>  #include "debug.h"
>  #include "pmus.h"
> +#include "target.h"
>  #include <linux/err.h>
>  
>  #define TEMPL "/tmp/perf-test-XXXXXX"
> @@ -37,11 +38,12 @@ static int session_write_header(char *path)
>  		.path = path,
>  		.mode = PERF_DATA_MODE_WRITE,
>  	};
> +	struct target target = {};
>  
>  	session = perf_session__new(&data, NULL);
>  	TEST_ASSERT_VAL("can't get session", !IS_ERR(session));
>  
> -	session->evlist = evlist__new_default();
> +	session->evlist = evlist__new_default(&target, /*sample_callchains=*/false);
>  	TEST_ASSERT_VAL("can't get evlist", session->evlist);
>  	session->evlist->session = session;
>  
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 591bdf0b3e2a..e6c518cc4a69 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -13,6 +13,7 @@
>  #include "util/mmap.h"
>  #include "thread_map.h"
>  #include "target.h"
> +#include "dwarf-regs.h"
>  #include "evlist.h"
>  #include "evsel.h"
>  #include "record.h"
> @@ -98,38 +99,44 @@ struct evlist *evlist__new(void)
>  	return evlist;
>  }
>  
> -struct evlist *evlist__new_default(void)
> +struct evlist *evlist__new_default(const struct target *target, bool sample_callchains)
>  {
>  	struct evlist *evlist = evlist__new();
>  	bool can_profile_kernel;
>  	struct perf_pmu *pmu = NULL;
> +	struct evsel *evsel;
> +	char buf[256];
> +	int err;
>  
>  	if (!evlist)
>  		return NULL;
>  
>  	can_profile_kernel = perf_event_paranoid_check(1);
>  
> -	while ((pmu = perf_pmus__scan_core(pmu)) != NULL) {
> -		char buf[256];
> -		int err;
> -
> -		snprintf(buf, sizeof(buf), "%s/cycles/%s", pmu->name,
> +	if (EM_HOST == EM_S390 && sample_callchains) {
> +		snprintf(buf, sizeof(buf), "software/%s/%s",
> +			 target__has_cpu(target) ? "cpu-clock" : "task-clock",
>  			 can_profile_kernel ? "P" : "Pu");
>  		err = parse_event(evlist, buf);
> -		if (err) {
> -			evlist__delete(evlist);
> -			return NULL;
> +		if (err)
> +			goto out_err;
> +	} else {
> +		while ((pmu = perf_pmus__scan_core(pmu)) != NULL) {
> +			snprintf(buf, sizeof(buf), "%s/cycles/%s", pmu->name,
> +				can_profile_kernel ? "P" : "Pu");
> +			err = parse_event(evlist, buf);
> +			if (err)
> +				goto out_err;
>  		}
>  	}
>  
> -	if (evlist->core.nr_entries > 1) {
> -		struct evsel *evsel;
> -
> -		evlist__for_each_entry(evlist, evsel)
> -			evsel__set_sample_id(evsel, /*can_sample_identifier=*/false);
> -	}
> +	evlist__for_each_entry(evlist, evsel)
> +		evsel__set_sample_id(evsel, /*can_sample_identifier=*/false);
>  
>  	return evlist;
> +out_err:
> +	evlist__delete(evlist);
> +	return NULL;
>  }
>  
>  struct evlist *evlist__new_dummy(void)
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index d17c3b57a409..e507f5f20ef6 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -104,7 +104,7 @@ struct evsel_str_handler {
>  };
>  
>  struct evlist *evlist__new(void);
> -struct evlist *evlist__new_default(void);
> +struct evlist *evlist__new_default(const struct target *target, bool sample_callchains);
>  struct evlist *evlist__new_dummy(void);
>  void evlist__init(struct evlist *evlist, struct perf_cpu_map *cpus,
>  		  struct perf_thread_map *threads);
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index bd14d9bbc91f..caa95dc06ac5 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1020,6 +1020,13 @@ static void __evsel__config_callchain(struct evsel *evsel, struct record_opts *o
>  {
>  	bool function = evsel__is_function_event(evsel);
>  	struct perf_event_attr *attr = &evsel->core.attr;
> +	enum perf_call_graph_mode record_mode = param->record_mode;
> +
> +	if (EM_HOST == EM_S390 && param->record_mode == CALLCHAIN_FP) {
> +		pr_warning("Framepointer unwinding switched to dwarf due to a lack of kernel support.\n"
> +			   "Use '--call-graph dwarf' to silence this warning.\n");
> +		record_mode = CALLCHAIN_DWARF;
> +	}
>  
>  	evsel__set_sample_bit(evsel, CALLCHAIN);
>  
> @@ -1029,7 +1036,7 @@ static void __evsel__config_callchain(struct evsel *evsel, struct record_opts *o
>  		attr->exclude_callchain_user = 1;
>  	if (opts->user_callchains)
>  		attr->exclude_callchain_kernel = 1;
> -	if (param->record_mode == CALLCHAIN_LBR) {
> +	if (record_mode == CALLCHAIN_LBR) {
>  		if (!opts->branch_stack) {
>  			if (attr->exclude_user) {
>  				pr_warning("LBR callstack option is only available "
> @@ -1048,7 +1055,7 @@ static void __evsel__config_callchain(struct evsel *evsel, struct record_opts *o
>  				    "Falling back to framepointers.\n");
>  	}
>  
> -	if (param->record_mode == CALLCHAIN_DWARF) {
> +	if (record_mode == CALLCHAIN_DWARF) {
>  		if (!function) {
>  			uint16_t e_machine = evsel__e_machine(evsel, /*e_flags=*/NULL);
>  

Ian, Thanks very much.

Tested-by: Thomas Richter <tmricht@linux.ibm.com>

The fall back to cpu-clock works nicely when --call-graph or -g is specified on s390.
-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

Vorsitzender des Aufsichtsrats: Wolfgang Wendt

Geschäftsführung: David Faller

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