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

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Message-ID: <CACbG30-ymdXDoMKSGvFDGBvnF5chHrbGOHXy5bxRM0L+uOrR9w@mail.gmail.com>
Date:	Wed, 22 Jun 2016 09:33:05 -0500
From:	Nilay Vaish <nilayvaish@...il.com>
To:	Wang Nan <wangnan0@...wei.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 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)

> +               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