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

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Message-ID: <723ddbe7-4d2d-592a-727f-5c2f46b3b8bb@huawei.com>
Date:   Sat, 13 Mar 2021 10:23:14 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     Namhyung Kim <namhyung@...nel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Yao Jin <yao.jin@...ux.intel.com>, <gustavoars@...nel.org>,
        <mliska@...e.cz>, linux-kernel <linux-kernel@...r.kernel.org>,
        <zhangjinhao2@...wei.com>
Subject: Re: [PATCH] perf annotate: Fix sample events lost in stdio mode

Hello,

On 2021/3/13 10:00, Yang Jihong wrote:
> 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@...wei.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@...wei.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@...wei.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/
> 
The first line of comments in the v3 patch is not empty
and has been modified. For details, see v4 patch:
https://lore.kernel.org/patchwork/patch/1394623/
Please review the new patch :)
>> Thanks,
>> Yang
>>> Thanks,
>>> Namhyung
> Thanks,
> Yang
>>> .
>>>
Thanks,
Yang