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

[Wangnan (F)]

On 2016/6/22 22:33, Nilay Vaish wrote:
> On 22 June 2016 at 04:08, Wang Nan <wangnan0@xxxxxxxxxx> 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