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Subject: Re: [RFC v1 05/16] perf kwork: Overwrite original atom in the list
 when a new atom is pushed.
To:     Ian Rogers <irogers@google.com>
CC:     <peterz@infradead.org>, <mingo@redhat.com>, <acme@kernel.org>,
        <mark.rutland@arm.com>, <alexander.shishkin@linux.intel.com>,
        <jolsa@kernel.org>, <namhyung@kernel.org>,
        <adrian.hunter@intel.com>, <kan.liang@linux.intel.com>,
        <sandipan.das@amd.com>, <ravi.bangoria@amd.com>,
        <linux-kernel@vger.kernel.org>, <linux-perf-users@vger.kernel.org>
References: <20230812084917.169338-1-yangjihong1@huawei.com>
 <20230812084917.169338-6-yangjihong1@huawei.com>
 <CAP-5=fWLmRWPdnxSG1AcyxzaupUAn9sX0M-dtDB1dd7-FCEhrw@mail.gmail.com>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <91cb7bea-3bec-b40c-24a2-be9052a30937@huawei.com>
Date:   Mon, 4 Sep 2023 19:46:02 +0800
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Hello,

On 2023/9/4 12:13, Ian Rogers wrote:
> On Sat, Aug 12, 2023 at 1:52 AM Yang Jihong <yangjihong1@huawei.com> wrote:
>>
>> work_push_atom() supports nesting. Currently, all supported kworks are not
>> nested. A `overwrite` parameter is added to overwrite the original atom in
>> the list.
>>
>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>> ---
>>   tools/perf/builtin-kwork.c | 24 ++++++++++++++++++------
>>   1 file changed, 18 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/perf/builtin-kwork.c b/tools/perf/builtin-kwork.c
>> index 42ea59a957ae..f620911a26a2 100644
>> --- a/tools/perf/builtin-kwork.c
>> +++ b/tools/perf/builtin-kwork.c
>> @@ -392,9 +392,10 @@ static int work_push_atom(struct perf_kwork *kwork,
>>                            struct evsel *evsel,
>>                            struct perf_sample *sample,
>>                            struct machine *machine,
>> -                         struct kwork_work **ret_work)
>> +                         struct kwork_work **ret_work,
>> +                         bool overwrite)
> 
> kerneldoc would be useful. Pushing something seems self-evident but
> what does overwrite mean without reading the code?

Okay, I'll add comments.

> 
>>   {
>> -       struct kwork_atom *atom, *dst_atom;
>> +       struct kwork_atom *atom, *dst_atom, *last_atom;
>>          struct kwork_work *work, key;
>>
>>          BUG_ON(class->work_init == NULL);
>> @@ -427,6 +428,17 @@ static int work_push_atom(struct perf_kwork *kwork,
>>          if (ret_work != NULL)
>>                  *ret_work = work;
>>
>> +       if (overwrite) {
>> +               last_atom = list_last_entry_or_null(&work->atom_list[src_type],
>> +                                                   struct kwork_atom, list);
>> +               if (last_atom) {
>> +                       atom_del(last_atom);
>> +
>> +                       kwork->nr_skipped_events[src_type]++;
>> +                       kwork->nr_skipped_events[KWORK_TRACE_MAX]++;
>> +               }
>> +       }
>> +
>>          list_add_tail(&atom->list, &work->atom_list[src_type]);
>>
>>          return 0;
>> @@ -502,7 +514,7 @@ static int report_entry_event(struct perf_kwork *kwork,
>>   {
>>          return work_push_atom(kwork, class, KWORK_TRACE_ENTRY,
>>                                KWORK_TRACE_MAX, evsel, sample,
>> -                             machine, NULL);
>> +                             machine, NULL, true);
> 
> nit: for constant arguments it can be useful to add parameter names
> which can enable checks like clang-tidy's bugprone argument:
> https://clang.llvm.org/extra/clang-tidy/checks/bugprone/argument-comment.html
> This would make this:
>          return work_push_atom(kwork, class, KWORK_TRACE_ENTRY,
>                                KWORK_TRACE_MAX, evsel, sample,
>                                machine, /*ret_work=*/NULL, /*overwite=*/true);
> 
Thanks for your advice, will add parameter names later.

Thanks,
Yang