Re: [RFC PATCH v1 2/5] perf stat: Fork and launch perf record when perf stat needs to get retire latency value for a metric.

[Namhyung Kim]

Hi,

On Wed, Feb 21, 2024 at 12:34 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> On Wed, Feb 21, 2024 at 9:52 AM Arnaldo Carvalho de Melo
> <acme@xxxxxxxxxx> wrote:
> >
> > On Wed, Feb 21, 2024 at 02:20:56AM -0500, weilin.wang@xxxxxxxxx wrote:
> > > From: Weilin Wang <weilin.wang@xxxxxxxxx>
> >
> > You wrote no description for this patch, please add one and show
> > examples of the feature being used, if possible.
> >
> > See below for more comments.
> >
> > > Signed-off-by: Weilin Wang <weilin.wang@xxxxxxxxx>
> > > +static int __cmd_script(struct child_process *cmd __maybe_unused)
> > > +{
> > > +     int err = 0;
> > > +     struct perf_session *session;
> > > +     struct perf_data data = {
> > > +             .mode = PERF_DATA_MODE_READ,
> > > +             .path = PERF_DATA,
> > > +             .fd   = cmd->out,
> > > +     };
> > > +     struct perf_script script = {
> > > +             .tool = {
> > > +             .sample          = process_sample_event,
> > > +             .ordered_events  = true,
> > > +             .ordering_requires_timestamps = true,
> > > +             .feature         = process_feature_event,
> > > +             .attr            = perf_event__process_attr,
> > > +             },
> > > +     };
> > > +     struct tpebs_event *e;
> > > +
> > > +     list_for_each_entry(e, &stat_config.tpebs_events, nd) {
> > > +             struct tpebs_retire_lat *new = malloc(sizeof(struct tpebs_retire_lat));
> > > +
> > > +             if (!new)
> > > +                     return -1;
> > > +             new->name = strdup(e->name);
> > > +             new->tpebs_name = strdup(e->tpebs_name);
> > > +             new->count = 0;
> > > +             new->sum = 0;
> >
> > Without even having thought that much about this overall architecture,
> > that looks too heavy at first sight, the above is done in tools/perf/
> > as:
> >
> > void tpebs_retire_lat__delete(struct tpebs_retire_lat *retire_lat)
> > {
> >         if (retire_lat == NULL)
> >                 return;
> >
> >         zfree(&retire_lat->tpebs_name);
> >         zfree(&retire_lat->tpebs_name);
> > }
> >
> > struct tpebs_retire_lat__new(tpebs_event *e)
> > {
> >         struct tpebs_retire_lat *retire_lat = zalloc(sizeof(*retire_lat));
> >
> >         if (retire_lat != NULL) {
> >                 retire_lat->name = strdup(e->name);
> >                 retire_lat->tpebs_name = strdup(e->tpebs_name);
> >
> >                 if (retire_lat->name == NULL || retire_lat->tpebs_name == NULL) {
> >                         tpebs_retire_lat__delete(retire_lat);
> >                         retire_lat = NULL;
> >                 }
> >         }
> >
> >         return retire_lat;
> > }
> >
> > And then you call the constructor  in that loop, and the destructor at
> > some point when those data structures are not needed.
> >
> > We do it because perf has a TUI mode and we may end up calling tools
> > from them in a long running session, so we need to avoid leaks.
> >
> > Also can we somehow hide Intel specific terms in arch specific files
> > while leaving something generic, possibly implementable in other arches
> > in the core code? I mean hiding clearly intel specific stuff like the
> > "tpebs" term in tools/perf/arch/x86/.
>
> Thanks Arnaldo, TPEBS support is necessary to support TMA metrics 4.7
> on meteorlake. The timed values replace hard coded constants that
> assume worst case latencies. You can see the metrics here:
> https://github.com/intel/perfmon/blob/main/TMA_Metrics-full.csv
> in the MTL (meteorlake) column row 29 there is:
> MEM_INST_RETIRED.STLB_HIT_LOADS*min($PEBS, #Mem_STLB_Hit_Cost) / CLKS
> + Load_STLB_Miss
> where the $PEBS is supposed to be replaced with the latency from a
> sample of MEM_INST_RETIRED.STLB_HIT_LOADS. There are meteorlake
> machines shipping but currently there are no perf metrics.
>
> Weilin raised the TPEBS problem in the LPC 2023 talk, the issue being
> that sampling and counting don't really exist in the current perf tool
> code at the same time. BPF could be a workaround but permissions are
> an issue. Perhaps leader sampling but then what to do if two latencies
> are needed. Forking perf to do this is an expedient and ideally we'd
> not do it.

Even with BPF, I think it needs two instances of an event - one for
counting and the other for sampling, right?  I wonder if it can just
use a single event for sampling and show the sum of periods in
PERF_SAMPLE_READ.

I'm not sure if an event group can have sampling and non-sampling
events at the same time.  But it can be done without groups then.
Anyway what's the issue with two latencies?

Thanks,
Namhyung

>
> I'm against stuff going in the arch directory in general. If something
> is specific to a PMU, let's special case the logic for that PMU in the
> tool. The arch directory gets us into messes like:
> https://lore.kernel.org/lkml/CAP-5=fVABSBZnsmtRn1uF-k-G1GWM-L5SgiinhPTfHbQsKXb_g@xxxxxxxxxxxxxx/
> Where a heterogenous/hybrid/big.little fix is in the x86 arch folder
> (overriding a weak symbol) but not in the arm or other ones leading to
> an arm bug.
>
> I think the idea of a count coming from an external or tool source is
> something of a more generic concept. I think what Weilin is doing here
> is setting the groundwork for doing that, a first implementation. I'd
> like the expr literals, like #smt_on, #num_cpus, etc. to be more like
> tool events such as duration_time. I think we can move in the
> direction that Weilin is adding here and then iterate to clean up
> these things, hopefully move them to events that then other tools
> could use, etc.
>
> Thanks,
> Ian
>
>
>
>
> > > +             list_add_tail(&new->nd, &stat_config.tpebs_results);
> > > +     }
> > > +
> > > +     kill(cmd->pid, SIGTERM);
> > > +     session = perf_session__new(&data, &script.tool);
> > > +     if (IS_ERR(session))
> > > +             return PTR_ERR(session);
> > > +     script.session = session;
> > > +     err = perf_session__process_events(session);
> > > +     perf_session__delete(session);
> > > +
> > > +     return err;
> > > +}
> > > +
> > >  static int __run_perf_stat(int argc, const char **argv, int run_idx)
> > >  {
> > >       int interval = stat_config.interval;
> > > @@ -709,12 +866,14 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
> > >       struct affinity saved_affinity, *affinity = NULL;
> > >       int err;
> > >       bool second_pass = false;
> > > +     struct child_process cmd;
> > >
> > >       //Prepare perf record for sampling event retire_latency before fork and prepare workload
> > >       if (stat_config.tpebs_event_size > 0) {
> > >               int ret;
> > >
> > > -             ret = __run_perf_record();
> > > +             pr_debug("perf stat pid = %d\n", getpid());
> > > +             ret = prepare_perf_record(&cmd);
> > >               if (ret)
> > >                       return ret;
> > >       }
> > > @@ -924,6 +1083,17 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
> > >
> > >       t1 = rdclock();
> > >
> > > +     if (stat_config.tpebs_event_size > 0) {
> > > +             int ret;
> > > +
> > > +             pr_debug("pid = %d\n", getpid());
> > > +             pr_debug("cmd.pid = %d\n", cmd.pid);
> > > +
> > > +             ret = __cmd_script(&cmd);
> > > +             close(cmd.out);
> > > +             pr_debug("%d\n", ret);
> > > +     }
> > > +
> > >       if (stat_config.walltime_run_table)
> > >               stat_config.walltime_run[run_idx] = t1 - t0;
> > >
> > > @@ -2714,6 +2884,7 @@ int cmd_stat(int argc, const char **argv)
> > >       }
> > >
> > >       INIT_LIST_HEAD(&stat_config.tpebs_events);
> > > +     INIT_LIST_HEAD(&stat_config.tpebs_results);
> > >
> > >       /*
> > >        * Metric parsing needs to be delayed as metrics may optimize events
> > > @@ -2921,5 +3092,7 @@ int cmd_stat(int argc, const char **argv)
> > >       metricgroup__rblist_exit(&stat_config.metric_events);
> > >       evlist__close_control(stat_config.ctl_fd, stat_config.ctl_fd_ack, &stat_config.ctl_fd_close);
> > >
> > > +     tpebs_data__delete();
> > > +
> > >       return status;
> > >  }
> > > diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
> > > index fc16299c915f..2298ca3b370b 100644
> > > --- a/tools/perf/util/data.c
> > > +++ b/tools/perf/util/data.c
> > > @@ -173,6 +173,10 @@ static bool check_pipe(struct perf_data *data)
> > >       int fd = perf_data__is_read(data) ?
> > >                STDIN_FILENO : STDOUT_FILENO;
> > >
> > > +     if (data->fd > 0) {
> > > +             fd = data->fd;
> > > +     }
> > > +
> > >       if (!data->path) {
> > >               if (!fstat(fd, &st) && S_ISFIFO(st.st_mode))
> > >                       is_pipe = true;
> > > diff --git a/tools/perf/util/data.h b/tools/perf/util/data.h
> > > index effcc195d7e9..5554d46ad212 100644
> > > --- a/tools/perf/util/data.h
> > > +++ b/tools/perf/util/data.h
> > > @@ -28,6 +28,7 @@ struct perf_data_file {
> > >
> > >  struct perf_data {
> > >       const char              *path;
> > > +     int                      fd;
> > >       struct perf_data_file    file;
> > >       bool                     is_pipe;
> > >       bool                     is_dir;
> > > diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> > > index 6c16e5a0b1fc..8518e2b3e5be 100644
> > > --- a/tools/perf/util/metricgroup.c
> > > +++ b/tools/perf/util/metricgroup.c
> > > @@ -691,8 +691,17 @@ static int metricgroup__build_event_string(struct strbuf *events,
> > >
> > >               if (p) {
> > >                       struct tpebs_event *new_event = malloc(sizeof(struct tpebs_event));
> > > -                     *p = '\0';
> > > +                     char *name;
> > > +
> > >                       new_event->tpebs_name = strdup(id);
> > > +                     *p = '\0';
> > > +                     name = malloc(strlen(id) + 2);
> > > +                     if (!name)
> > > +                             return -ENOMEM;
> > > +
> > > +                     strcpy(name, id);
> > > +                     strcat(name, ":p");
> > > +                     new_event->name = name;
> >
> > For such cases we use asprintf(), that allocates and formats the string
> > in one call, look for examples in other tools/perf/ files.
> >
> > >                       *tpebs_event_size += 1;
> > >                       pr_debug("retire_latency required, tpebs_event_size=%lu, new_event=%s\n",
> > >                       *tpebs_event_size, new_event->name);
> > > diff --git a/tools/perf/util/metricgroup.h b/tools/perf/util/metricgroup.h
> > > index 7c24ed768ff3..1fa12cc3294e 100644
> > > --- a/tools/perf/util/metricgroup.h
> > > +++ b/tools/perf/util/metricgroup.h
> > > @@ -71,6 +71,13 @@ struct tpebs_event {
> > >       const char *name;
> > >       const char *tpebs_name;
> > >  };
> > > +struct tpebs_retire_lat {
> > > +     struct list_head nd;
> > > +     const char *name;
> > > +     const char *tpebs_name;
> > > +     size_t count;
> > > +     int sum;
> > > +};
> >
> > Here you declare the constructor and destructor I suggested above.
> >
> > >  struct metric_event *metricgroup__lookup(struct rblist *metric_events,
> > >                                        struct evsel *evsel,
> > > diff --git a/tools/perf/util/stat.h b/tools/perf/util/stat.h
> > > index 9d0186316b29..8e180f13aa2d 100644
> > > --- a/tools/perf/util/stat.h
> > > +++ b/tools/perf/util/stat.h
> > > @@ -111,6 +111,9 @@ struct perf_stat_config {
> > >       struct rblist            metric_events;
> > >       struct list_head         tpebs_events;
> > >       size_t                   tpebs_event_size;
> > > +     struct list_head         tpebs_results;
> > > +     pid_t                    tpebs_pid;
> > > +     int                      tpebs_pipe;
> > >       int                      ctl_fd;
> > >       int                      ctl_fd_ack;
> > >       bool                     ctl_fd_close;
> > > --
> > > 2.43.0
> > >