linux-kernel - Re: [PATCH 1/9] perf/core: Add PERF_RECORD

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Date:   Fri, 30 Aug 2019 09:34:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 1/9] perf/core: Add PERF_RECORD_CGROUP event

On Fri, Aug 30, 2019 at 12:46:51PM +0900, Namhyung Kim wrote:
> Hi Peter,
> 
> On Wed, Aug 28, 2019 at 6:45 PM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Wed, Aug 28, 2019 at 04:31:22PM +0900, Namhyung Kim wrote:
> > > To support cgroup tracking, add CGROUP event to save a link between
> > > cgroup path and inode number.  The attr.cgroup bit was also added to
> > > enable cgroup tracking from userspace.
> > >
> > > This event will be generated when a new cgroup becomes active.
> > > Userspace might need to synthesize those events for existing cgroups.
> > >
> > > As aux_output change is also going on, I just added the bit here as
> > > well to remove possible conflicts later.
> >
> > Why do we want this?
> 
> I saw below [1] and thought you have the patch introduced aux_output
> and it's gonna to be merged soon.
> Also the tooling patches are already in the acme/perf/core
> so I just wanted to avoid conflicts.
> 
> Anyway, I'm ok with changing it.  Will remove in v2.

I seem to have confused both you and Arnaldo with this. This email
questions the Changelog as a whole, not just the aux thing (I send a
separate email for that).

This Changelog utterly fails to explain to me _why_ we need/want cgroup
tracking. So why do I want to review and possibly merge this? Changelog
needs to answer this.