Re: [PATCH v2 2/2] perf stat: Stop repeating when ref_perf_stat() returns -1

[James Clark]

On 13/09/2024 09:36, James Clark wrote:
> On 13/09/2024 03:02, Levi Yun wrote:
> > Exit when run_perf_stat() returns an error to avoid continuously
> > repeating the same error message. It's not expected that COUNTER_FATAL
> > or internal errors are recoverable so there's no point in retrying.
> >
> > This fixes the following flood of error messages for permission issues,
> > for example when perf_event_paranoid==3:
> >    perf stat -r 1044 -- false
> >
> >    Error:
> >    Access to performance monitoring and observability operations is 
> > limited.
> >    ...
> >    Error:
> >    Access to performance monitoring and observability operations is 
> > limited.
> >    ...
> >    (repeating for 1044 times).
> >
> > Signed-off-by: Levi Yun <yeoreum.yun@xxxxxxx>
> > ---
> > Changes in v2:
> >    - Add some comments.
> > ---
> >   tools/perf/builtin-stat.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> > index 954eb37ce7b8..0153925f2382 100644
> > --- a/tools/perf/builtin-stat.c
> > +++ b/tools/perf/builtin-stat.c
> > @@ -2875,7 +2875,15 @@ int cmd_stat(int argc, const char **argv)
> >               evlist__reset_prev_raw_counts(evsel_list);
> >
> >           status = run_perf_stat(argc, argv, run_idx);
> > -        if (forever && status != -1 && !interval) {
> > +        /*
> > +         * * Meet COUNTER_FATAL situation (i.e) can't open event 
> > counter.
> > +         * * In this case, there is a high chance of failure in the 
> > next attempt
> > +         * * as well with the same reason. so, stop it.
> > +         * */
>
> There's something wrong with the formatting here.
>
> But I don't think the comment answers my question about the other return 
> codes. It just states what the code does.
>
> There are many more return -1's than just for COUNTER_FATAL, so it's not 
> just that situation anyway. And in addition to that, there is -ENOMEM 
> and others that aren't -1 which aren't explained that they are 
> deliberately explicit retry or ignores.

If I'm understanding what I think it means, what about something like this:

/*
 * Returns -1 for fatal errors which signifies to not continue
 * when in repeat mode.
 *
 * Returns < -1 error codes when stat record is used. These
 * result in the stat information being displayed, but writing
 * to the file fails and is non fatal.
 */
static int __run_perf_stat(int argc, const char **argv, int run_idx)
{