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

[Yang Jihong <yangjihong1@huawei.com>]

Hello, Namhyung
On 2021/3/12 18:20, Yang Jihong wrote:
> Hello,
> 
> On 2021/3/12 16:39, Namhyung Kim wrote:
>> 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.  :)
>>
> OK, :)
>>
>>>>>> 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).
>>
> OK, I'll submit a v3 patch based on the "changing the sort order" solution.
> 
I have submitted the v3 patch, look forward to your review:
https://lore.kernel.org/patchwork/patch/1394619/

> Thanks,
> Yang
>> Thanks,
>> Namhyung
Thanks,
Yang
>> .
>>