linux-kernel - Re: [PATCH v9 5/8] perf record: Toggle overwrite ring buffer for reading

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Date:	Thu, 23 Jun 2016 09:19:31 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Nilay Vaish <nilayvaish@...il.com>
CC:	<acme@...nel.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	<pi3orama@....com>, He Kuang <hekuang@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>
Subject: Re: [PATCH v9 5/8] perf record: Toggle overwrite ring buffer for
 reading



On 2016/6/22 22:33, Nilay Vaish wrote:
> On 22 June 2016 at 04:08, Wang Nan <wangnan0@...wei.com> wrote:
>> @@ -549,17 +573,72 @@ static struct perf_event_header finished_round_event = {
>>          .type = PERF_RECORD_FINISHED_ROUND,
>>   };
>>
>> -static int record__mmap_read_all(struct record *rec)
>> +static void
>> +record__toggle_overwrite_evsels(struct record *rec,
>> +                               enum overwrite_evt_state state)
>> +{
>> +       struct perf_evlist *evlist = rec->overwrite_evlist;
>> +       enum overwrite_evt_state old_state = rec->overwrite_evt_state;
>> +       enum action {
>> +               NONE,
>> +               PAUSE,
>> +               RESUME,
>> +       } action = NONE;
>> +
>> +       switch (old_state) {
>> +       case OVERWRITE_EVT_RUNNING:
>> +               if (state != OVERWRITE_EVT_RUNNING)
>> +                       action = PAUSE;
>> +               break;
>> +       case OVERWRITE_EVT_DATA_PENDING:
>> +               if (state == OVERWRITE_EVT_RUNNING)
>> +                       action = RESUME;
>> +               break;
>> +       case OVERWRITE_EVT_EMPTY:
>> +               if (state == OVERWRITE_EVT_RUNNING)
>> +                       action = RESUME;
>> +               if (state == OVERWRITE_EVT_DATA_PENDING)
>> +                       state = OVERWRITE_EVT_EMPTY;
> else if (state == OVERWRITE_EVT_DATA_PENDING)

You are right, but I believe compiler makes identical binaries even
without 'else'. With no 'else' these two 'if' are aligned.

I'll recheck this patch.

>> +               break;
>> +       default:
>> +               WARN_ONCE(1, "Shouldn't get there\n");
>> +       }
>> +
>> +       rec->overwrite_evt_state = state;
>> +
>> +       if (action == NONE)
>> +               return;
> I think the above two lines are not required.  The switch below should
> be enough.
>
>> +
>> +       if (!evlist)
>> +               return;
>> +
>> +       switch (action) {
>> +       case PAUSE:
>> +               perf_evlist__pause(evlist);
>> +               break;
>> +       case RESUME:
>> +               perf_evlist__resume(evlist);
>> +               break;
>> +       case NONE:
>> +       default:
>> +               break;
>> +       }
>> +}
>> +
> --
> Nilay