Re: [PATCH 1/2] perf: Use sample_flags for addr

[Namhyung Kim]

Hi Peter,

On Thu, Sep 22, 2022 at 7:48 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Sep 21, 2022 at 03:00:31PM -0700, Namhyung Kim wrote:
> > Use the new sample_flags to indicate whether the addr field is filled by
> > the PMU driver.  As most PMU drivers pass 0, it can set the flag only if
> > it has a non-zero value.  And use 0 in perf_sample_output() if it's not
> > filled already.
>
> So no objection to the general idea; just a question
>
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 368bdc4f563f..f4a13579b0e8 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -1028,7 +1028,6 @@ struct perf_sample_data {
> >        * minimize the cachelines touched.
> >        */
> >       u64                             sample_flags;
> > -     u64                             addr;
> >       struct perf_raw_record          *raw;
> >       u64                             period;
> >
> > @@ -1040,6 +1039,7 @@ struct perf_sample_data {
> >       union perf_sample_weight        weight;
> >       union  perf_mem_data_src        data_src;
> >       u64                             txn;
> > +     u64                             addr;
> >
> >       u64                             type;
> >       u64                             ip;
>
> Is there a reason you placed the variable where you did?

No I just followed the previous change.

>
> I'm thinking we should look at what perf-tool thinks is the common set
> of SAMPLE flags and make sure those fields are grouped in as little
> cachelines as possible.
>
> Things like @ip and @type, which are basically *always* set, should
> definitely be on top, no?

Yes, you're right.  With this change we can move the optional fields
and group the common fields on top - like ip, period, pid and so on.

Will send a patch to do the move on top of this, ok?

Thanks,
Namhyung