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Date:   Wed, 17 Oct 2018 13:06:51 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Song Liu <songliubraving@fb.com>
Cc:     Alexey Budankov <alexey.budankov@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
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        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Stephane Eranian <eranian@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>,
        "megha.dey@intel.com" <megha.dey@intel.com>,
        "frederic@kernel.org" <frederic@kernel.org>
Subject: Re: [RFC][PATCH] perf: Rewrite core context handling
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On Tue, Oct 16, 2018 at 06:28:10PM +0000, Song Liu wrote:
> > How about this:=20
> >=20
> > 1. Keep multiple perf_cpu_context per CPU, just like before this patch.=
=20
> >=20
> > 2. For perf_event_context, add PMU as an order for the RB tree.=20
> >=20
> > 3. (hw) pmu->perf_cpu_context->ctx only has events for this PMU (and sw=
=20
> >   events moved to this context).
> >=20
> > 4. task->perf_event_ctxp has events for all PMUs.=20
> >=20
> > With this path, we keep the existing perf_cpu_context/perf_event_context
> > logic as-is, which I think is simp=10ler than the new logic (with extra
> > *_pmu_context). And it should also solve the problem.=20
> >=20
> > Does this make sense? If this doesn't look too broken, I am happy to
> > draft RFC for it.=20
> >=20
>=20
> I am not sure whether you missed this one, or found it totally insane.=20
> Could you please share your comments on it? My gut feeling is that this=
=20
> would be a simpler patch to solve the problem (two hw PMUs). (It might=20
> be less efficient though).=20

Ah, sorry, somehow this email got lost.

That makes task and cpu contexts wildly different, which will complicate
matters I feel.