Re: [PATCH v2 5/7] perf evlist: Skip dummy event sample_type check for evlist_config

[Yang Jihong]

Hello,

On 2023/7/18 17:56, Adrian Hunter wrote:
> On 18/07/23 12:30, Yang Jihong wrote:
> > Hello,
> >
> > On 2023/7/17 22:41, Adrian Hunter wrote:
> > > On 15/07/23 06:29, Yang Jihong wrote:
> > > > The dummp event does not contain sampls data. Therefore, sample_type does
> > > > not need to be checked.
> > > >
> > > > Currently, the sample id format of the actual sampling event may be changed
> > > > after the dummy event is added.
> > > >
> > > > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> > > > ---
> > > >    tools/perf/util/record.c | 7 +++++++
> > > >    1 file changed, 7 insertions(+)
> > > >
> > > > diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
> > > > index 9eb5c6a08999..0240be3b340f 100644
> > > > --- a/tools/perf/util/record.c
> > > > +++ b/tools/perf/util/record.c
> > > > @@ -128,6 +128,13 @@ void evlist__config(struct evlist *evlist, struct record_opts *opts, struct call
> > > >            evlist__for_each_entry(evlist, evsel) {
> > > >                if (evsel->core.attr.sample_type == first->core.attr.sample_type)
> > > >                    continue;
> > > > +
> > > > +            /*
> > > > +             * Skip the sample_type check for the dummy event
> > > > +             * because it does not have any samples anyway.
> > > > +             */
> > > > +            if (evsel__is_dummy_event(evsel))
> > > > +                continue;
> > >
> > > Sideband event records have "ID samples" so the sample type still matters.
> > Okay, will remove this patch in next version.
> >
> > Can I ask a little more about this?
> >
> > Use PERF_SAMPLE_IDENTIFICATION instead of PERF_SAMPLE_ID because for samples of type PERF_RECORD_SAMPLE, there may be different record formats due to different *sample_type* settings, so the fixed SAMPLE_ID  location mode PERF_SAMPLE_NAME is required here.
> >
> > However, for the sideband event, the samples of the PERF_RECORD_SAMPLE type is not recorded (only PERF_RECORD_MMAP, PERF_RECORD_COMM, and so on). Therefore, the "use sample identifier "check can be skipped here.
> >
> > That's my understanding of PERF_SAMPLE_IDENTIFICATION . If there is any error, please help to correct it.
> >
> > *Sideband event records have "ID samples" so the sample type still matters.*
> >
> > Does this mean that sideband will also record samples of type PERF_RECORD_SAMPLE? What exactly is the sampling data?
>
> No.  There are additional members as defined by struct sample_id for PERF_RECORD_MMAP:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/perf_event.h?h=v6.4#n872
I'm sorry, maybe my comments didn't make it clear.
I mean, can we skip the "use_sample_identifier" check here?

That is, set sample_type to *XXX|PERF_SAMPLE_ID* instead of 
*XXX|PERF_SAMPLE_IDENTIFICATION*

Thanks,
Yang