Messages in this thread | | | From | Ian Rogers <> | Date | Tue, 14 Apr 2020 07:38:17 -0700 | Subject | Re: [PATCH] perf stat: force error in fallback on :k events |
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On Tue, Apr 14, 2020 at 6:02 AM Jiri Olsa <jolsa@redhat.com> wrote: > > On Mon, Apr 13, 2020 at 04:55:15PM -0700, Ian Rogers wrote: > > From: Stephane Eranian <eranian@google.com> > > > > When it is not possible for a non-privilege perf command > > to monitor at the kernel level (:k), the fallback code forces > > a :u. That works if the event was previously monitoring both levels. > > But if the event was already constrained to kernel only, then it does > > not make sense to restrict it to user only. > > Given the code works by exclusion, a kernel only event would have: > > attr->exclude_user = 1 > > The fallback code would add: > > attr->exclude_kernel = 1; > > > > In the end the end would not monitor in either the user level or kernel > > level. In other words, it would count nothing. > > > > An event programmed to monitor kernel only cannot be switched to user only > > without seriously warning the user. > > > > This patch forces an error in this case to make it clear the request > > cannot really be satisfied. > > > > Signed-off-by: Stephane Eranian <eranian@google.com> > > Reviewed-by: Ian Rogers <irogers@google.com> > > --- > > tools/perf/util/evsel.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c > > index d23db6755f51..d1e8862b86ce 100644 > > --- a/tools/perf/util/evsel.c > > +++ b/tools/perf/util/evsel.c > > @@ -2446,6 +2446,13 @@ bool perf_evsel__fallback(struct evsel *evsel, int err, > > char *new_name; > > const char *sep = ":"; > > > > + if (evsel->core.attr.exclude_user) { > > + scnprintf(msg, msgsize, > > +"kernel.perf_event_paranoid=%d, event set to exclude user, so cannot also exclude kernel", > > + paranoid); > > + return false; > > I'm not able to get this error printed, it seems to be > overwritten by perf_evsel__open_strerror call > > please include perf example with the new output
Agreed, it is possible the change builtin-top/sched/record so that on error the msg is checked and dumped in verbose mode. I think it is also fine to just remove the scnprintf. Do you have a preference?
Thanks, Ian
> thanks, > jirka > > > + } > > + > > /* Is there already the separator in the name. */ > > if (strchr(name, '/') || > > strchr(name, ':')) > > -- > > 2.26.0.110.g2183baf09c-goog > > >
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