Re: [PATCH] perf annotate: Fix sample events lost in stdio mode

[Yang Jihong]

Hello, Namhyung

On 2021/3/11 22:42, Namhyung Kim wrote:
> Hi,
>
> On Thu, Mar 11, 2021 at 5:48 PM Yang Jihong <yangjihong1@xxxxxxxxxx> wrote:
> > Hello,
> >
> > On 2021/3/6 16:28, Yang Jihong wrote:
> > > In hist__find_annotations function, since have a hist_entry per IP for the same
> > > symbol, we free notes->src to signal already processed this symbol in stdio mode;
> > > when annotate, entry will skipped if notes->src is NULL to avoid repeated output.
>
> I'm not sure it's still true that we have a hist_entry per IP.
> Afaik the default sort key is comm,dso,sym which means it should have a single
> hist_entry for each symbol.  It seems like an old comment..
Emm, yes, we have a hist_entry for per IP.
a member named "sym" in struct "hist_entry" points to symbol,
different IP may point to the same symbol.

The hist_entry struct is as follows:
struct hist_entry {
    ...
    struct map_symbol ms;
    ...
};
struct map_symbol {
    struct maps *maps;
    struct map *map;
    struct symbol *sym;
};

> > > However, there is a problem, for example, run the following command:
> > >
> > >    # perf record -e branch-misses -e branch-instructions -a sleep 1
> > >
> > > perf.data file contains different types of sample event.
> > >
> > > If the same IP sample event exists in branch-misses and branch-instructions,
> > > this event uses the same symbol. When annotate branch-misses events, notes->src
> > > corresponding to this event is set to null, as a result, when annotate
> > > branch-instructions events, this event is skipped and no annotate is output.
> > >
> > > Solution of this patch is to add a u8 member to struct sym_hist and use a bit to
> > > indicate whether the symbol has been processed.
> > > Because different types of event correspond to different sym_hist, no conflict
> > > occurs.
> > > ---
> > >    tools/perf/builtin-annotate.c | 22 ++++++++++++++--------
> > >    tools/perf/util/annotate.h    |  4 ++++
> > >    2 files changed, 18 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/tools/perf/builtin-annotate.c b/tools/perf/builtin-annotate.c
> > > index a23ba6bb99b6..c8c67892ae82 100644
> > > --- a/tools/perf/builtin-annotate.c
> > > +++ b/tools/perf/builtin-annotate.c
> > > @@ -372,15 +372,21 @@ static void hists__find_annotations(struct hists *hists,
> > >                        if (next != NULL)
> > >                                nd = next;
> > >                } else {
> > > -                     hist_entry__tty_annotate(he, evsel, ann);
> > > +                     struct sym_hist *h = annotated_source__histogram(notes->src,
> > > +                                                                      evsel->idx);
> > > +
> > > +                     if (h->processed == 0) {
> > > +                             hist_entry__tty_annotate(he, evsel, ann);
> > > +
> > > +                             /*
> > > +                              * Since we have a hist_entry per IP for the same
> > > +                              * symbol, set processed flag of evsel in sym_hist
> > > +                              * to signal we already processed this symbol.
> > > +                              */
> > > +                             h->processed = 1;
> > > +                     }
> > > +
> > >                        nd = rb_next(nd);
> > > -                     /*
> > > -                      * Since we have a hist_entry per IP for the same
> > > -                      * symbol, free he->ms.sym->src to signal we already
> > > -                      * processed this symbol.
> > > -                      */
> > > -                     zfree(&notes->src->cycles_hist);
> > > -                     zfree(&notes->src);
> > >                }
> > >        }
> > >    }
> > > diff --git a/tools/perf/util/annotate.h b/tools/perf/util/annotate.h
> > > index 096cdaf21b01..89872bfdc958 100644
> > > --- a/tools/perf/util/annotate.h
> > > +++ b/tools/perf/util/annotate.h
> > > @@ -228,6 +228,10 @@ void symbol__calc_percent(struct symbol *sym, struct evsel *evsel);
> > >    struct sym_hist {
> > >        u64                   nr_samples;
> > >        u64                   period;
> > > +
> > > +     u8                    processed  : 1, /* whether symbol has been processed, used for annotate */
> > > +                           __reserved : 7;
>
> I think just a bool member is fine.
OK, I have submitted the v2 patch and changed to bool member, new patch 
is as follows, look forward to your review:
https://lore.kernel.org/patchwork/patch/1393901/

> > > +
> > >        struct sym_hist_entry addr[];
> > >    };
> > Please check whether this solution is feasible, look forward to your review.
>
> What about this?  (not tested)
>
> diff --git a/tools/perf/builtin-annotate.c b/tools/perf/builtin-annotate.c
> index a23ba6bb99b6..a91fe45bd69f 100644
> --- a/tools/perf/builtin-annotate.c
> +++ b/tools/perf/builtin-annotate.c
> @@ -374,13 +374,6 @@ static void hists__find_annotations(struct hists *hists,
>                  } else {
>                          hist_entry__tty_annotate(he, evsel, ann);
>                          nd = rb_next(nd);
> -                       /*
> -                        * Since we have a hist_entry per IP for the same
> -                        * symbol, free he->ms.sym->src to signal we already
> -                        * processed this symbol.
> -                        */
> -                       zfree(&notes->src->cycles_hist);
> -                       zfree(&notes->src);
>                  }
>          }
>   }
This solution may have the following problem:
For example, if two sample events are in two different processes but in 
the same symbol, repeated output may occur.
Therefore, a flag is required to indicate whether the symbol has been 
processed to avoid repeated output.
> Thanks,
> Namhyung
> .
Thanks,
Yang
.