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

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Mar 12, 2021 at 4:19 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>
>
> Hello,
> On 2021/3/12 13:49, Namhyung Kim wrote:
> > Hi,
> >
> > On Fri, Mar 12, 2021 at 12:24 PM Yang Jihong <yangjihong1@huawei.com> wrote:
> >>
> >> Hello, Namhyung
> >>
> >> On 2021/3/11 22:42, Namhyung Kim wrote:
> >>> Hi,
> >>>
> >>> On Thu, Mar 11, 2021 at 5:48 PM Yang Jihong <yangjihong1@huawei.com> 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.
> >
> > Are you sure about this?  It seems like a bug then.
> >
> Yes, now each IP corresponds to a hist_entry :)
>
> Last week I found that some sample events were missing when perf
> annotate in stdio mode, so I went through the annotate code carefully.
>
> The event handling process is as follows:
> process_sample_event
>    evsel_add_sample
>      hists__add_entry
>        __hists__add_entry
>          hists__findnew_entry
>            hist_entry__new                  -> here allock new hist_entry

Yeah, so this is for a symbol.

>
>      hist_entry__inc_addr_samples
>        symbol__inc_addr_samples
>          symbol__hists
>            annotated_source__new            -> here alloc annotate soruce
>            annotated_source__alloc_histograms -> here alloc histograms

This should be for each IP (ideally it should be per instruction).

>
> By bugs, do you mean there's something wrong?

No. I think we were saying about different things.  :)


> >>> 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.
> >
> > Hmm.. ok.  Yeah we don't care about the processes here.
> > Then we should remove it from the sort key like below:
> >
> > @@ -624,6 +617,7 @@ int cmd_annotate(int argc, const char **argv)
> >                  if (setup_sorting(annotate.session->evlist) < 0)
> >                          usage_with_options(annotate_usage, options);
> >          } else {
> > +               sort_order = "dso,symbol";
> >                  if (setup_sorting(NULL) < 0)
> >                          usage_with_options(annotate_usage, options);
> >          }
> >
> >
> Are you referring to this solution?
> --- 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);
>                  }
>          }
>   }
> @@ -624,6 +617,7 @@ int cmd_annotate(int argc, const char **argv)
>                  if (setup_sorting(annotate.session->evlist) < 0)
>                          usage_with_options(annotate_usage, options);
>          } else {
> +               sort_order = "dso,symbol";
>                  if (setup_sorting(NULL) < 0)
>                          usage_with_options(annotate_usage, options);
>          }
> It seems to be a better solution without adding new member.
> I just tested it and it works.
>
> If we decide to use this solution, I'll resubmit a v3 patch.

I prefer changing the sort order (and removing the zfree and comments).

Thanks,
Namhyung