[RFC PATCH v2] perf evsel: Fallback to task-clock when not system wide

[RFC PATCH v2] perf evsel: Fallback to task-clock when not system wide

[Ian Rogers]

When the cycles event isn't available evsel will fallback to the
cpu-clock software event. task-clock is similar to cpu-clock but only
runs when the process is running. Falling back to cpu-clock when not
system wide leads to confusion, by falling back to task-clock it is
hoped the confusion is less.

Pass the target to determine if task-clock is more appropriate. Update
a nearby comment and debug string for the change.

---
v2. Use target__has_cpu as suggested by Namhyung.
https://lpc.events/event/17/contributions/1556/

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/builtin-record.c |  2 +-
 tools/perf/builtin-stat.c   |  2 +-
 tools/perf/builtin-top.c    |  2 +-
 tools/perf/util/evsel.c     | 18 ++++++++++--------
 tools/perf/util/evsel.h     |  3 ++-
 5 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 8ec818568662..d8bb59511fdd 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1350,7 +1350,7 @@ static int record__open(struct record *rec)
 	evlist__for_each_entry(evlist, pos) {
 try_again:
 		if (evsel__open(pos, pos->core.cpus, pos->core.threads) < 0) {
-			if (evsel__fallback(pos, errno, msg, sizeof(msg))) {
+			if (evsel__fallback(pos, &opts->target, errno, msg, sizeof(msg))) {
 				if (verbose > 0)
 					ui__warning("%s\n", msg);
 				goto try_again;
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index a3af805a1d57..d8e5d6f7a87a 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -653,7 +653,7 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
 		if ((evsel__leader(counter) != counter) ||
 		    !(counter->core.leader->nr_members > 1))
 			return COUNTER_SKIP;
-	} else if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
+	} else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
 		if (verbose > 0)
 			ui__warning("%s\n", msg);
 		return COUNTER_RETRY;
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index ea8c7eca5eee..1e42bd1c7d5a 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1044,7 +1044,7 @@ static int perf_top__start_counters(struct perf_top *top)
 			    perf_top_overwrite_fallback(top, counter))
 				goto try_again;
 
-			if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
+			if (evsel__fallback(counter, &opts->target, errno, msg, sizeof(msg))) {
 				if (verbose > 0)
 					ui__warning("%s\n", msg);
 				goto try_again;
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a5da74e3a517..532f34d9fcb5 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2853,7 +2853,8 @@ u64 evsel__intval_common(struct evsel *evsel, struct perf_sample *sample, const
 
 #endif
 
-bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
+bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
+		     char *msg, size_t msgsize)
 {
 	int paranoid;
 
@@ -2861,18 +2862,19 @@ bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
 	    evsel->core.attr.type   == PERF_TYPE_HARDWARE &&
 	    evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
 		/*
-		 * If it's cycles then fall back to hrtimer based
-		 * cpu-clock-tick sw counter, which is always available even if
-		 * no PMU support.
+		 * If it's cycles then fall back to hrtimer based cpu-clock sw
+		 * counter, which is always available even if no PMU support.
 		 *
 		 * PPC returns ENXIO until 2.6.37 (behavior changed with commit
 		 * b0a873e).
 		 */
-		scnprintf(msg, msgsize, "%s",
-"The cycles event is not supported, trying to fall back to cpu-clock-ticks");
-
 		evsel->core.attr.type   = PERF_TYPE_SOFTWARE;
-		evsel->core.attr.config = PERF_COUNT_SW_CPU_CLOCK;
+		evsel->core.attr.config = target__has_cpu(target)
+			? PERF_COUNT_SW_CPU_CLOCK
+			: PERF_COUNT_SW_TASK_CLOCK;
+		scnprintf(msg, msgsize,
+			"The cycles event is not supported, trying to fall back to %s",
+			target__has_cpu(target) ? "cpu-clock" : "task-clock");
 
 		zfree(&evsel->name);
 		return true;
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index f19ac9f027ef..efbb6e848287 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -460,7 +460,8 @@ static inline bool evsel__is_clock(const struct evsel *evsel)
 	       evsel__match(evsel, SOFTWARE, SW_TASK_CLOCK);
 }
 
-bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize);
+bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
+		     char *msg, size_t msgsize);
 int evsel__open_strerror(struct evsel *evsel, struct target *target,
 			 int err, char *msg, size_t size);
 
-- 
2.43.0.rc1.413.gea7ed67945-goog

Re: [RFC PATCH v2] perf evsel: Fallback to task-clock when not system wide

[Ian Rogers]

On Mon, Nov 20, 2023 at 4:04 PM Ian Rogers <irogers@google.com> wrote:
>
> When the cycles event isn't available evsel will fallback to the
> cpu-clock software event. task-clock is similar to cpu-clock but only
> runs when the process is running. Falling back to cpu-clock when not
> system wide leads to confusion, by falling back to task-clock it is
> hoped the confusion is less.
>
> Pass the target to determine if task-clock is more appropriate. Update
> a nearby comment and debug string for the change.
>
> ---
> v2. Use target__has_cpu as suggested by Namhyung.
> https://lpc.events/event/17/contributions/1556/
>
> Signed-off-by: Ian Rogers <irogers@google.com>

Ping.

Thanks,
Ian

> ---
>  tools/perf/builtin-record.c |  2 +-
>  tools/perf/builtin-stat.c   |  2 +-
>  tools/perf/builtin-top.c    |  2 +-
>  tools/perf/util/evsel.c     | 18 ++++++++++--------
>  tools/perf/util/evsel.h     |  3 ++-
>  5 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 8ec818568662..d8bb59511fdd 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1350,7 +1350,7 @@ static int record__open(struct record *rec)
>         evlist__for_each_entry(evlist, pos) {
>  try_again:
>                 if (evsel__open(pos, pos->core.cpus, pos->core.threads) < 0) {
> -                       if (evsel__fallback(pos, errno, msg, sizeof(msg))) {
> +                       if (evsel__fallback(pos, &opts->target, errno, msg, sizeof(msg))) {
>                                 if (verbose > 0)
>                                         ui__warning("%s\n", msg);
>                                 goto try_again;
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index a3af805a1d57..d8e5d6f7a87a 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -653,7 +653,7 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
>                 if ((evsel__leader(counter) != counter) ||
>                     !(counter->core.leader->nr_members > 1))
>                         return COUNTER_SKIP;
> -       } else if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
> +       } else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
>                 if (verbose > 0)
>                         ui__warning("%s\n", msg);
>                 return COUNTER_RETRY;
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index ea8c7eca5eee..1e42bd1c7d5a 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -1044,7 +1044,7 @@ static int perf_top__start_counters(struct perf_top *top)
>                             perf_top_overwrite_fallback(top, counter))
>                                 goto try_again;
>
> -                       if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
> +                       if (evsel__fallback(counter, &opts->target, errno, msg, sizeof(msg))) {
>                                 if (verbose > 0)
>                                         ui__warning("%s\n", msg);
>                                 goto try_again;
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index a5da74e3a517..532f34d9fcb5 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2853,7 +2853,8 @@ u64 evsel__intval_common(struct evsel *evsel, struct perf_sample *sample, const
>
>  #endif
>
> -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
> +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
> +                    char *msg, size_t msgsize)
>  {
>         int paranoid;
>
> @@ -2861,18 +2862,19 @@ bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
>             evsel->core.attr.type   == PERF_TYPE_HARDWARE &&
>             evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
>                 /*
> -                * If it's cycles then fall back to hrtimer based
> -                * cpu-clock-tick sw counter, which is always available even if
> -                * no PMU support.
> +                * If it's cycles then fall back to hrtimer based cpu-clock sw
> +                * counter, which is always available even if no PMU support.
>                  *
>                  * PPC returns ENXIO until 2.6.37 (behavior changed with commit
>                  * b0a873e).
>                  */
> -               scnprintf(msg, msgsize, "%s",
> -"The cycles event is not supported, trying to fall back to cpu-clock-ticks");
> -
>                 evsel->core.attr.type   = PERF_TYPE_SOFTWARE;
> -               evsel->core.attr.config = PERF_COUNT_SW_CPU_CLOCK;
> +               evsel->core.attr.config = target__has_cpu(target)
> +                       ? PERF_COUNT_SW_CPU_CLOCK
> +                       : PERF_COUNT_SW_TASK_CLOCK;
> +               scnprintf(msg, msgsize,
> +                       "The cycles event is not supported, trying to fall back to %s",
> +                       target__has_cpu(target) ? "cpu-clock" : "task-clock");
>
>                 zfree(&evsel->name);
>                 return true;
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index f19ac9f027ef..efbb6e848287 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -460,7 +460,8 @@ static inline bool evsel__is_clock(const struct evsel *evsel)
>                evsel__match(evsel, SOFTWARE, SW_TASK_CLOCK);
>  }
>
> -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize);
> +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
> +                    char *msg, size_t msgsize);
>  int evsel__open_strerror(struct evsel *evsel, struct target *target,
>                          int err, char *msg, size_t size);
>
> --
> 2.43.0.rc1.413.gea7ed67945-goog
>

Re: [RFC PATCH v2] perf evsel: Fallback to task-clock when not system wide

[Namhyung Kim]

On Mon, Dec 4, 2023 at 8:02 AM Ian Rogers <irogers@google.com> wrote:
>
> On Mon, Nov 20, 2023 at 4:04 PM Ian Rogers <irogers@google.com> wrote:
> >
> > When the cycles event isn't available evsel will fallback to the
> > cpu-clock software event. task-clock is similar to cpu-clock but only
> > runs when the process is running. Falling back to cpu-clock when not
> > system wide leads to confusion, by falling back to task-clock it is
> > hoped the confusion is less.
> >
> > Pass the target to determine if task-clock is more appropriate. Update
> > a nearby comment and debug string for the change.
> >
> > ---
> > v2. Use target__has_cpu as suggested by Namhyung.
> > https://lpc.events/event/17/contributions/1556/
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>

Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung

Re: [RFC PATCH v2] perf evsel: Fallback to task-clock when not system wide

[Athira Rajeev]

> On 21-Nov-2023, at 5:34 AM, Ian Rogers <irogers@google.com> wrote:
> 
> When the cycles event isn't available evsel will fallback to the
> cpu-clock software event. task-clock is similar to cpu-clock but only
> runs when the process is running. Falling back to cpu-clock when not
> system wide leads to confusion, by falling back to task-clock it is
> hoped the confusion is less.
> 
> Pass the target to determine if task-clock is more appropriate. Update
> a nearby comment and debug string for the change.
> 
> ---
> v2. Use target__has_cpu as suggested by Namhyung.
> https://lpc.events/event/17/contributions/1556/
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/builtin-record.c |  2 +-
> tools/perf/builtin-stat.c   |  2 +-
> tools/perf/builtin-top.c    |  2 +-
> tools/perf/util/evsel.c     | 18 ++++++++++--------
> tools/perf/util/evsel.h     |  3 ++-
> 5 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 8ec818568662..d8bb59511fdd 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1350,7 +1350,7 @@ static int record__open(struct record *rec)
> evlist__for_each_entry(evlist, pos) {
> try_again:
> if (evsel__open(pos, pos->core.cpus, pos->core.threads) < 0) {
> - if (evsel__fallback(pos, errno, msg, sizeof(msg))) {
> + if (evsel__fallback(pos, &opts->target, errno, msg, sizeof(msg))) {

Hi Ian

Tested this with perf record and I could find the code fallback to using task-clock

./perf record -v ls
Warning:
The cycles event is not supported, trying to fall back to task-clock

But in case of “perf stat”, in my environment, found that the code path won't invoke “evsel__fallback”.

Snippet for builtin-stat.c
            if (errno == EINVAL || errno == ENOSYS ||
            errno == ENOENT || errno == EOPNOTSUPP ||
            errno == ENXIO) {
                if (verbose > 0)
                        ui__warning("%s event is not supported by the kernel.\n",
                                    evsel__name(counter));
                counter->supported = false;
                /*
                 * errored is a sticky flag that means one of the counter's
                 * cpu event had a problem and needs to be reexamined.
                 */
                counter->errored = true;

                if ((evsel__leader(counter) != counter) ||
                    !(counter->core.leader->nr_members > 1))
                        return COUNTER_SKIP;
        } else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
                if (verbose > 0)
                        ui__warning("%s\n", msg);
                return COUNTER_RETRY;

So if the perf_event_open returns ENOENT, we won’t do a fallback in builtin-stat.c
Should we address cycles differently here ? Any comments ?

Thanks
Athira
>   
> if (verbose > 0)
> ui__warning("%s\n", msg);
> goto try_again;
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index a3af805a1d57..d8e5d6f7a87a 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -653,7 +653,7 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
> if ((evsel__leader(counter) != counter) ||
>    !(counter->core.leader->nr_members > 1))
> return COUNTER_SKIP;
> - } else if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
> + } else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
> if (verbose > 0)
> ui__warning("%s\n", msg);
> return COUNTER_RETRY;
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index ea8c7eca5eee..1e42bd1c7d5a 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -1044,7 +1044,7 @@ static int perf_top__start_counters(struct perf_top *top)
>    perf_top_overwrite_fallback(top, counter))
> goto try_again;
> 
> - if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
> + if (evsel__fallback(counter, &opts->target, errno, msg, sizeof(msg))) {
> if (verbose > 0)
> ui__warning("%s\n", msg);
> goto try_again;
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index a5da74e3a517..532f34d9fcb5 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2853,7 +2853,8 @@ u64 evsel__intval_common(struct evsel *evsel, struct perf_sample *sample, const
> 
> #endif
> 
> -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
> +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
> +     char *msg, size_t msgsize)
> {
> int paranoid;
> 
> @@ -2861,18 +2862,19 @@ bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
>    evsel->core.attr.type   == PERF_TYPE_HARDWARE &&
>    evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
> /*
> - * If it's cycles then fall back to hrtimer based
> - * cpu-clock-tick sw counter, which is always available even if
> - * no PMU support.
> + * If it's cycles then fall back to hrtimer based cpu-clock sw
> + * counter, which is always available even if no PMU support.
> *
> * PPC returns ENXIO until 2.6.37 (behavior changed with commit
> * b0a873e).
> */
> - scnprintf(msg, msgsize, "%s",
> -"The cycles event is not supported, trying to fall back to cpu-clock-ticks");
> -
> evsel->core.attr.type   = PERF_TYPE_SOFTWARE;
> - evsel->core.attr.config = PERF_COUNT_SW_CPU_CLOCK;
> + evsel->core.attr.config = target__has_cpu(target)
> + ? PERF_COUNT_SW_CPU_CLOCK
> + : PERF_COUNT_SW_TASK_CLOCK;
> + scnprintf(msg, msgsize,
> + "The cycles event is not supported, trying to fall back to %s",
> + target__has_cpu(target) ? "cpu-clock" : "task-clock");
> 
> zfree(&evsel->name);
> return true;
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index f19ac9f027ef..efbb6e848287 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -460,7 +460,8 @@ static inline bool evsel__is_clock(const struct evsel *evsel)
>       evsel__match(evsel, SOFTWARE, SW_TASK_CLOCK);
> }
> 
> -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize);
> +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
> +     char *msg, size_t msgsize);
> int evsel__open_strerror(struct evsel *evsel, struct target *target,
> int err, char *msg, size_t size);
> 
> -- 
> 2.43.0.rc1.413.gea7ed67945-goog
> 

Re: [RFC PATCH v2] perf evsel: Fallback to task-clock when not system wide

[Arnaldo Carvalho de Melo]

Em Tue, Dec 05, 2023 at 04:51:01PM +0530, Athira Rajeev escreveu:
> 
> 
> > On 21-Nov-2023, at 5:34 AM, Ian Rogers <irogers@google.com> wrote:
> > 
> > When the cycles event isn't available evsel will fallback to the
> > cpu-clock software event. task-clock is similar to cpu-clock but only
> > runs when the process is running. Falling back to cpu-clock when not
> > system wide leads to confusion, by falling back to task-clock it is
> > hoped the confusion is less.
> > 
> > Pass the target to determine if task-clock is more appropriate. Update
> > a nearby comment and debug string for the change.
> > 
> > ---
> > v2. Use target__has_cpu as suggested by Namhyung.
> > https://lpc.events/event/17/contributions/1556/
> > 
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> > tools/perf/builtin-record.c |  2 +-
> > tools/perf/builtin-stat.c   |  2 +-
> > tools/perf/builtin-top.c    |  2 +-
> > tools/perf/util/evsel.c     | 18 ++++++++++--------
> > tools/perf/util/evsel.h     |  3 ++-
> > 5 files changed, 15 insertions(+), 12 deletions(-)
> > 
> > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > index 8ec818568662..d8bb59511fdd 100644
> > --- a/tools/perf/builtin-record.c
> > +++ b/tools/perf/builtin-record.c
> > @@ -1350,7 +1350,7 @@ static int record__open(struct record *rec)
> > evlist__for_each_entry(evlist, pos) {
> > try_again:
> > if (evsel__open(pos, pos->core.cpus, pos->core.threads) < 0) {
> > - if (evsel__fallback(pos, errno, msg, sizeof(msg))) {
> > + if (evsel__fallback(pos, &opts->target, errno, msg, sizeof(msg))) {
> 
> Hi Ian
> 
> Tested this with perf record and I could find the code fallback to using task-clock
> 
> ./perf record -v ls
> Warning:
> The cycles event is not supported, trying to fall back to task-clock

Ok, so I'll take that as a Tested-by: you, ok?

The "perf stat" part can be addressed in a follow up patch, when that
error handling is researched to remember why we have that ->supported,
->errored thing.

- Arnaldo
 
> But in case of “perf stat”, in my environment, found that the code path won't invoke “evsel__fallback”.
> 
> Snippet for builtin-stat.c
>             if (errno == EINVAL || errno == ENOSYS ||
>             errno == ENOENT || errno == EOPNOTSUPP ||
>             errno == ENXIO) {
>                 if (verbose > 0)
>                         ui__warning("%s event is not supported by the kernel.\n",
>                                     evsel__name(counter));
>                 counter->supported = false;
>                 /*
>                  * errored is a sticky flag that means one of the counter's
>                  * cpu event had a problem and needs to be reexamined.
>                  */
>                 counter->errored = true;
> 
>                 if ((evsel__leader(counter) != counter) ||
>                     !(counter->core.leader->nr_members > 1))
>                         return COUNTER_SKIP;
>         } else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
>                 if (verbose > 0)
>                         ui__warning("%s\n", msg);
>                 return COUNTER_RETRY;
> 
> So if the perf_event_open returns ENOENT, we won’t do a fallback in builtin-stat.c
> Should we address cycles differently here ? Any comments ?
> 
> Thanks
> Athira
> >   
> > if (verbose > 0)
> > ui__warning("%s\n", msg);
> > goto try_again;
> > diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> > index a3af805a1d57..d8e5d6f7a87a 100644
> > --- a/tools/perf/builtin-stat.c
> > +++ b/tools/perf/builtin-stat.c
> > @@ -653,7 +653,7 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
> > if ((evsel__leader(counter) != counter) ||
> >    !(counter->core.leader->nr_members > 1))
> > return COUNTER_SKIP;
> > - } else if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
> > + } else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
> > if (verbose > 0)
> > ui__warning("%s\n", msg);
> > return COUNTER_RETRY;
> > diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> > index ea8c7eca5eee..1e42bd1c7d5a 100644
> > --- a/tools/perf/builtin-top.c
> > +++ b/tools/perf/builtin-top.c
> > @@ -1044,7 +1044,7 @@ static int perf_top__start_counters(struct perf_top *top)
> >    perf_top_overwrite_fallback(top, counter))
> > goto try_again;
> > 
> > - if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
> > + if (evsel__fallback(counter, &opts->target, errno, msg, sizeof(msg))) {
> > if (verbose > 0)
> > ui__warning("%s\n", msg);
> > goto try_again;
> > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > index a5da74e3a517..532f34d9fcb5 100644
> > --- a/tools/perf/util/evsel.c
> > +++ b/tools/perf/util/evsel.c
> > @@ -2853,7 +2853,8 @@ u64 evsel__intval_common(struct evsel *evsel, struct perf_sample *sample, const
> > 
> > #endif
> > 
> > -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
> > +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
> > +     char *msg, size_t msgsize)
> > {
> > int paranoid;
> > 
> > @@ -2861,18 +2862,19 @@ bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
> >    evsel->core.attr.type   == PERF_TYPE_HARDWARE &&
> >    evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
> > /*
> > - * If it's cycles then fall back to hrtimer based
> > - * cpu-clock-tick sw counter, which is always available even if
> > - * no PMU support.
> > + * If it's cycles then fall back to hrtimer based cpu-clock sw
> > + * counter, which is always available even if no PMU support.
> > *
> > * PPC returns ENXIO until 2.6.37 (behavior changed with commit
> > * b0a873e).
> > */
> > - scnprintf(msg, msgsize, "%s",
> > -"The cycles event is not supported, trying to fall back to cpu-clock-ticks");
> > -
> > evsel->core.attr.type   = PERF_TYPE_SOFTWARE;
> > - evsel->core.attr.config = PERF_COUNT_SW_CPU_CLOCK;
> > + evsel->core.attr.config = target__has_cpu(target)
> > + ? PERF_COUNT_SW_CPU_CLOCK
> > + : PERF_COUNT_SW_TASK_CLOCK;
> > + scnprintf(msg, msgsize,
> > + "The cycles event is not supported, trying to fall back to %s",
> > + target__has_cpu(target) ? "cpu-clock" : "task-clock");
> > 
> > zfree(&evsel->name);
> > return true;
> > diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> > index f19ac9f027ef..efbb6e848287 100644
> > --- a/tools/perf/util/evsel.h
> > +++ b/tools/perf/util/evsel.h
> > @@ -460,7 +460,8 @@ static inline bool evsel__is_clock(const struct evsel *evsel)
> >       evsel__match(evsel, SOFTWARE, SW_TASK_CLOCK);
> > }
> > 
> > -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize);
> > +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
> > +     char *msg, size_t msgsize);
> > int evsel__open_strerror(struct evsel *evsel, struct target *target,
> > int err, char *msg, size_t size);
> > 
> > -- 
> > 2.43.0.rc1.413.gea7ed67945-goog
> > 
> 

-- 

- Arnaldo

Re: [RFC PATCH v2] perf evsel: Fallback to task-clock when not system wide

[Athira Rajeev]

> On 05-Dec-2023, at 8:55 PM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> 
> Em Tue, Dec 05, 2023 at 04:51:01PM +0530, Athira Rajeev escreveu:
>> 
>> 
>>> On 21-Nov-2023, at 5:34 AM, Ian Rogers <irogers@google.com> wrote:
>>> 
>>> When the cycles event isn't available evsel will fallback to the
>>> cpu-clock software event. task-clock is similar to cpu-clock but only
>>> runs when the process is running. Falling back to cpu-clock when not
>>> system wide leads to confusion, by falling back to task-clock it is
>>> hoped the confusion is less.
>>> 
>>> Pass the target to determine if task-clock is more appropriate. Update
>>> a nearby comment and debug string for the change.
>>> 
>>> ---
>>> v2. Use target__has_cpu as suggested by Namhyung.
>>> https://lpc.events/event/17/contributions/1556/
>>> 
>>> Signed-off-by: Ian Rogers <irogers@google.com>
>>> ---
>>> tools/perf/builtin-record.c |  2 +-
>>> tools/perf/builtin-stat.c   |  2 +-
>>> tools/perf/builtin-top.c    |  2 +-
>>> tools/perf/util/evsel.c     | 18 ++++++++++--------
>>> tools/perf/util/evsel.h     |  3 ++-
>>> 5 files changed, 15 insertions(+), 12 deletions(-)
>>> 
>>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>>> index 8ec818568662..d8bb59511fdd 100644
>>> --- a/tools/perf/builtin-record.c
>>> +++ b/tools/perf/builtin-record.c
>>> @@ -1350,7 +1350,7 @@ static int record__open(struct record *rec)
>>> evlist__for_each_entry(evlist, pos) {
>>> try_again:
>>> if (evsel__open(pos, pos->core.cpus, pos->core.threads) < 0) {
>>> - if (evsel__fallback(pos, errno, msg, sizeof(msg))) {
>>> + if (evsel__fallback(pos, &opts->target, errno, msg, sizeof(msg))) {
>> 
>> Hi Ian
>> 
>> Tested this with perf record and I could find the code fallback to using task-clock
>> 
>> ./perf record -v ls
>> Warning:
>> The cycles event is not supported, trying to fall back to task-clock
> 
> Ok, so I'll take that as a Tested-by: you, ok?

Hi Arnaldo,

Please add my Tested-by.

Tested-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>

> 
> The "perf stat" part can be addressed in a follow up patch, when that
> error handling is researched to remember why we have that ->supported,
> ->errored thing.

Sure, I will take a look at why we have that difference in “perf stat”

Thanks
Athira
> 
> - Arnaldo
> 
>> But in case of “perf stat”, in my environment, found that the code path won't invoke “evsel__fallback”.
>> 
>> Snippet for builtin-stat.c
>>            if (errno == EINVAL || errno == ENOSYS ||
>>            errno == ENOENT || errno == EOPNOTSUPP ||
>>            errno == ENXIO) {
>>                if (verbose > 0)
>>                        ui__warning("%s event is not supported by the kernel.\n",
>>                                    evsel__name(counter));
>>                counter->supported = false;
>>                /*
>>                 * errored is a sticky flag that means one of the counter's
>>                 * cpu event had a problem and needs to be reexamined.
>>                 */
>>                counter->errored = true;
>> 
>>                if ((evsel__leader(counter) != counter) ||
>>                    !(counter->core.leader->nr_members > 1))
>>                        return COUNTER_SKIP;
>>        } else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
>>                if (verbose > 0)
>>                        ui__warning("%s\n", msg);
>>                return COUNTER_RETRY;
>> 
>> So if the perf_event_open returns ENOENT, we won’t do a fallback in builtin-stat.c
>> Should we address cycles differently here ? Any comments ?
>> 
>> Thanks
>> Athira
>>> 
>>> if (verbose > 0)
>>> ui__warning("%s\n", msg);
>>> goto try_again;
>>> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
>>> index a3af805a1d57..d8e5d6f7a87a 100644
>>> --- a/tools/perf/builtin-stat.c
>>> +++ b/tools/perf/builtin-stat.c
>>> @@ -653,7 +653,7 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
>>> if ((evsel__leader(counter) != counter) ||
>>>   !(counter->core.leader->nr_members > 1))
>>> return COUNTER_SKIP;
>>> - } else if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
>>> + } else if (evsel__fallback(counter, &target, errno, msg, sizeof(msg))) {
>>> if (verbose > 0)
>>> ui__warning("%s\n", msg);
>>> return COUNTER_RETRY;
>>> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
>>> index ea8c7eca5eee..1e42bd1c7d5a 100644
>>> --- a/tools/perf/builtin-top.c
>>> +++ b/tools/perf/builtin-top.c
>>> @@ -1044,7 +1044,7 @@ static int perf_top__start_counters(struct perf_top *top)
>>>   perf_top_overwrite_fallback(top, counter))
>>> goto try_again;
>>> 
>>> - if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
>>> + if (evsel__fallback(counter, &opts->target, errno, msg, sizeof(msg))) {
>>> if (verbose > 0)
>>> ui__warning("%s\n", msg);
>>> goto try_again;
>>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>>> index a5da74e3a517..532f34d9fcb5 100644
>>> --- a/tools/perf/util/evsel.c
>>> +++ b/tools/perf/util/evsel.c
>>> @@ -2853,7 +2853,8 @@ u64 evsel__intval_common(struct evsel *evsel, struct perf_sample *sample, const
>>> 
>>> #endif
>>> 
>>> -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
>>> +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
>>> +     char *msg, size_t msgsize)
>>> {
>>> int paranoid;
>>> 
>>> @@ -2861,18 +2862,19 @@ bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize)
>>>   evsel->core.attr.type   == PERF_TYPE_HARDWARE &&
>>>   evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
>>> /*
>>> - * If it's cycles then fall back to hrtimer based
>>> - * cpu-clock-tick sw counter, which is always available even if
>>> - * no PMU support.
>>> + * If it's cycles then fall back to hrtimer based cpu-clock sw
>>> + * counter, which is always available even if no PMU support.
>>> *
>>> * PPC returns ENXIO until 2.6.37 (behavior changed with commit
>>> * b0a873e).
>>> */
>>> - scnprintf(msg, msgsize, "%s",
>>> -"The cycles event is not supported, trying to fall back to cpu-clock-ticks");
>>> -
>>> evsel->core.attr.type   = PERF_TYPE_SOFTWARE;
>>> - evsel->core.attr.config = PERF_COUNT_SW_CPU_CLOCK;
>>> + evsel->core.attr.config = target__has_cpu(target)
>>> + ? PERF_COUNT_SW_CPU_CLOCK
>>> + : PERF_COUNT_SW_TASK_CLOCK;
>>> + scnprintf(msg, msgsize,
>>> + "The cycles event is not supported, trying to fall back to %s",
>>> + target__has_cpu(target) ? "cpu-clock" : "task-clock");
>>> 
>>> zfree(&evsel->name);
>>> return true;
>>> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
>>> index f19ac9f027ef..efbb6e848287 100644
>>> --- a/tools/perf/util/evsel.h
>>> +++ b/tools/perf/util/evsel.h
>>> @@ -460,7 +460,8 @@ static inline bool evsel__is_clock(const struct evsel *evsel)
>>>      evsel__match(evsel, SOFTWARE, SW_TASK_CLOCK);
>>> }
>>> 
>>> -bool evsel__fallback(struct evsel *evsel, int err, char *msg, size_t msgsize);
>>> +bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
>>> +     char *msg, size_t msgsize);
>>> int evsel__open_strerror(struct evsel *evsel, struct target *target,
>>> int err, char *msg, size_t size);
>>> 
>>> -- 
>>> 2.43.0.rc1.413.gea7ed67945-goog
>>> 
>> 
> 
> -- 
> 
> - Arnaldo