Re: [PATCH v5 5/5] perf evlist: Improve default event for s390

Ian Rogers
2026-03-17T15:54:18Z

On Tue, Mar 17, 2026 at 12:52 AM Thomas Richter <tmricht@linux.ibm.com> wrote:
>
> On 3/17/26 06:53, 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 show a
> > warning. Modify the '-g' option of `perf top` and `perf record` to
> > default to dwarf callchains on s390.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> > tools/perf/builtin-record.c | 8 ++++++--
> > tools/perf/builtin-top.c | 5 +++--
> > 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 | 32 +++++++++++++++++++++-----------
> > tools/perf/util/evlist.h | 2 +-
> > tools/perf/util/evsel.c | 5 +++++
> > 9 files changed, 50 insertions(+), 21 deletions(-)
> >
> > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > index af1fe6b7c65c..ef97c7a54088 100644
> > --- a/tools/perf/builtin-record.c
> > +++ b/tools/perf/builtin-record.c
> > @@ -55,6 +55,7 @@
> > #include "asm/bug.h"
> > #include "perf.h"
> > #include "cputopo.h"
> > +#include "dwarf-regs.h"
> >
> > #include <errno.h>
> > #include <inttypes.h>
> > @@ -2986,7 +2987,9 @@ static int record_callchain_opt(const struct option *opt,
> > const char *arg __maybe_unused,
> > int unset)
> > {
> > - return record_opts__parse_callchain(opt->value, &callchain_param, "fp", unset);
> > + return record_opts__parse_callchain(opt->value, &callchain_param,
> > + EM_HOST != EM_S390 ? "fp" : "dwarf",
> > + unset);
> > }
> >
> >
> > @@ -4265,7 +4268,8 @@ 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 2a949d956d0b..84211a78977e 100644
> > --- a/tools/perf/builtin-top.c
> > +++ b/tools/perf/builtin-top.c
> > @@ -56,6 +56,7 @@
> > #include "util/debug.h"
> > #include "util/ordered-events.h"
> > #include "util/pfm.h"
> > +#include "dwarf-regs.h"
> >
> > #include <assert.h>
> > #include <elf.h>
> > @@ -1409,7 +1410,7 @@ parse_callchain_opt(const struct option *opt, const char *arg, int unset)
> > static int
> > callchain_opt(const struct option *opt, const char *arg __maybe_unused, int unset)
> > {
> > - return parse_callchain_opt(opt, "fp", unset);
> > + return parse_callchain_opt(opt, EM_HOST != EM_S390 ? "fp" : "dwarf", unset);
> > }
> >
> >
> > @@ -1695,7 +1696,7 @@ 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..c702741a9173 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 +99,47 @@ 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 there is only 1 event a sample identifier isn't necessary. */
> > if (evlist->core.nr_entries > 1) {
> > - struct evsel *evsel;
> > -
> > 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 54c8922a8e47..5a294595a677 100644
> > --- a/tools/perf/util/evsel.c
> > +++ b/tools/perf/util/evsel.c
> > @@ -1021,6 +1021,11 @@ static void __evsel__config_callchain(struct evsel *evsel, const struct record_o
> > bool function = evsel__is_function_event(evsel);
> > struct perf_event_attr *attr = &evsel->core.attr;
> >
> > + if (EM_HOST == EM_S390 && param->record_mode == CALLCHAIN_FP) {
> > + pr_warning_once(
> > + "Framepointer unwinding lacks kernel support. Use '--call-graph dwarf'\n");
> > + }
> > +
> > evsel__set_sample_bit(evsel, CALLCHAIN);
> >
> > attr->sample_max_stack = param->max_stack;
>
> Great, here is the output on my LPAR. Thanks very much fpr addressing and fixing this!!!
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc took 2s
> ❯ ./perf record --call-graph dwarf -- perf test -w noploop
> [ perf record: Woken up 133 times to write data ]
> [ perf record: Captured and wrote 32.928 MB perf.data (4039 samples) ]
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc took 2s
> ❯ ./perf evlist
> software/task-clock/P
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc
> ❯ ./perf record -g -- perf test -w noploop
> [ perf record: Woken up 133 times to write data ]
> [ perf record: Captured and wrote 32.952 MB perf.data (4042 samples) ]
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc took 2s
> ❯ ./perf evlist
> software/task-clock/P
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc
> ❯ ./perf record -- perf test -w noploop
> [ perf record: Woken up 2 times to write data ]
> [ perf record: Captured and wrote 0.179 MB perf.data (3974 samples) ]
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc took 2s
> ❯ ./perf evlist
> cpum_cf/cycles/P
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc
> ❯ ./perf record
> ^C[ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.250 MB perf.data (24 samples) ]
>
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc took 3s
> ❯ ./perf evlist
> cpum_cf/cycles/P
> dummy:u
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc
> ❯ ./perf record -g
> ^C[ perf record: Woken up 8 times to write data ]
> [ perf record: Captured and wrote 5.186 MB perf.data (34255 samples) ]
>
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc took 3s
> ❯ ./perf evlist
> software/cpu-clock/P
> dummy:u
>
>
> root in 🌐 b83lp69 in mirror-linux-next/tools/perf on  master [⇡] via C v15.2.1-gcc took 3s
>
> Tested-by: Thomas Richter <tmricht@linux.ibm.com>

Thanks Thomas! I'll add the tag into the next version. Why a new
version? I'm trying to appease sashiko that is rightly flagging more
issues:
https://sashiko.dev/#/patchset/20260317055334.760347-1-irogers%40google.com

Thanks,
Ian

> --
> Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
> --
> IBM Deutschland Research & Development GmbH
>
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