Re: [PATCH V3 1/5] perf/core: Add PERF_SAMPLE_WEIGHT_STRUCT

[Liang, Kan]

On 2/5/2021 5:43 AM, Namhyung Kim wrote:
> On Fri, Feb 5, 2021 at 12:24 AM Liang, Kan <kan.liang@xxxxxxxxxxxxxxx> wrote:
> > On 2/4/2021 9:00 AM, Namhyung Kim wrote:
> > > Hi Kan,
> > >
> > > On Sat, Jan 30, 2021 at 2:25 AM Liang, Kan <kan.liang@xxxxxxxxxxxxxxx> wrote:
> > > [SNIP]
> > > > diff --git a/include/uapi/linux/perf_event.h
> > > > b/include/uapi/linux/perf_event.h
> > > > index b15e344..c50718a 100644
> > > > --- a/include/uapi/linux/perf_event.h
> > > > +++ b/include/uapi/linux/perf_event.h
> > > > @@ -145,12 +145,14 @@ enum perf_event_sample_format {
> > > >           PERF_SAMPLE_CGROUP                      = 1U << 21,
> > > >           PERF_SAMPLE_DATA_PAGE_SIZE              = 1U << 22,
> > > >           PERF_SAMPLE_CODE_PAGE_SIZE              = 1U << 23,
> > > > +       PERF_SAMPLE_WEIGHT_STRUCT               = 1U << 24,
> > > >
> > > > -       PERF_SAMPLE_MAX = 1U << 24,             /* non-ABI */
> > > > +       PERF_SAMPLE_MAX = 1U << 25,             /* non-ABI */
> > > >
> > > >           __PERF_SAMPLE_CALLCHAIN_EARLY           = 1ULL << 63, /* non-ABI; internal use */
> > > >     };
> > > >
> > > > +#define PERF_SAMPLE_WEIGHT_TYPE        (PERF_SAMPLE_WEIGHT |
> > > > PERF_SAMPLE_WEIGHT_STRUCT)
> > >
> > > I'm not sure you want to expose it in the uapi header as it's not
> > > intended to be used IMHO.
> >
> > I'm not sure I understood, but it's indeed used in the tool patch set.
> >
> > https://lore.kernel.org/lkml/1612296553-21962-6-git-send-email-kan.liang@xxxxxxxxxxxxxxx/
>
> Well, it's not a big deal.. but I just worried if some users might do
>
>    event.attr.sample_type = PERF_SAMPLE_WEIGHT_TYPE;

Yes, it's possible. For this case, Kernel returns -EINVAL.

Actually, even without the macro, users may still set PERF_SAMPLE_WEIGHT 
| PERF_SAMPLE_WEIGHT_STRUCT manually. We cannot control what a user 
sets. I don't think it's a problem as long as the kernel can handle it 
properly.

Thanks,
Kan