Re: [PATCH] arm64: dts: allwinner: a64: Drop PMU node

From: Vasily Khoruzhick <anarsoul@gmail.com>
To: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree <devicetree@vger.kernel.org>,
	"Jared D . McNeill" <jmcneill@netbsd.org>,
	Chen-Yu Tsai <wens@csie.org>, Rob Herring <robh+dt@kernel.org>,
	Harald Geyer <harald@ccbib.org>,
	Robin Murphy <robin.murphy@arm.com>,
	arm-linux <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] arm64: dts: allwinner: a64: Drop PMU node
Date: Wed, 7 Aug 2019 10:36:08 -0700	[thread overview]
Message-ID: <CA+E=qVdh3MHMsEC9XKe5-7O8fGTHFh76WLOgVf+PZPv7c4JE9w@mail.gmail.com> (raw)
In-Reply-To: <20190807115614.phm7sbyae6yajkug@flea>

On Wed, Aug 7, 2019 at 4:56 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
>
> On Tue, Aug 06, 2019 at 07:39:26PM -0700, Vasily Khoruzhick wrote:
> > On Tue, Aug 6, 2019 at 2:14 PM Robin Murphy <robin.murphy@arm.com> wrote:
> > >
> > > On 2019-08-06 9:52 pm, Vasily Khoruzhick wrote:
> > > > On Tue, Aug 6, 2019 at 1:19 PM Harald Geyer <harald@ccbib.org> wrote:
> > > >>
> > > >> Vasily Khoruzhick writes:
> > > >>> On Tue, Aug 6, 2019 at 7:35 AM Robin Murphy <robin.murphy@arm.com> wrote:
> > > >>>>
> > > >>>> On 06/08/2019 15:01, Vasily Khoruzhick wrote:
> > > >>>>> Looks like PMU in A64 is broken, it generates no interrupts at all and
> > > >>>>> as result 'perf top' shows no events.
> > > >>>>
> > > >>>> Does something like 'perf stat sleep 1' at least count cycles correctly?
> > > >>>> It could well just be that the interrupt numbers are wrong...
> > > >>>
> > > >>> Looks like it does, at least result looks plausible:
> > > >>
> > > >> I'm using perf stat regularly (cache benchmarks) and it works fine.
> > > >>
> > > >> Unfortunately I wasn't aware that perf stat is a poor test for
> > > >> the interrupts part of the node, when I added it. So I'm not too
> > > >> surprised I got it wrong.
> > > >>
> > > >> However, it would be unfortunate if the node got removed completely,
> > > >> because perf stat would not work anymore. Maybe we can only remove
> > > >> the interrupts or just fix them even if the HW doesn't work?
> > > >
> > > > I'm not familiar with PMU driver. Is it possible to get it working
> > > > without interrupts?
> > >
> > > Yup - you get a grumpy message from the driver, it will refuse sampling
> > > events (the ones which weren't working anyway), and if you measure
> > > anything for long enough that a counter overflows you'll get wonky
> > > results. But for counting hardware events over relatively short periods
> > > it'll still do the job.
> >
> > I tried to drop interrupts completely from the node but 'perf top' is
> > still broken. Though now in different way: it complains "cycles: PMU
> > Hardware doesn't support sampling/overflow-interrupts. Try 'perf
> > stat'"
>
> I have no idea if that's the culprit, but what is the state of the
> 0x09010000 register?

What register is that and how do I check it?

> (in particular, are the bits 16-19 and 24 set or not?
>
> Maxime
>
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

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