From: Marc Zyngier <maz@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>,
Hector Martin <marcan@marcan.st>, Sven Peter <sven@svenpeter.dev>,
Alyssa Rosenzweig <alyssa@rosenzweig.io>,
Rob Herring <robh+dt@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Dougall <dougallj@gmail.com>,
kernel-team@android.com
Subject: Re: [PATCH v2 8/8] drivers/perf: Add Apple icestorm/firestorm CPU PMU driver
Date: Fri, 03 Dec 2021 16:22:44 +0000 [thread overview]
Message-ID: <871r2tmze3.wl-maz@kernel.org> (raw)
In-Reply-To: <YaoH07BzWSLKQ6K3@FVFF77S0Q05N>
On Fri, 03 Dec 2021 12:04:35 +0000,
Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Fri, Dec 03, 2021 at 11:22:53AM +0000, Marc Zyngier wrote:
> > On Thu, 02 Dec 2021 16:14:01 +0000, Mark Rutland <mark.rutland@arm.com> wrote:
> > > On Thu, Dec 02, 2021 at 03:39:46PM +0000, Marc Zyngier wrote:
> > > > On Wed, 01 Dec 2021 16:58:10 +0000, Mark Rutland <mark.rutland@arm.com> wrote:
> > > > > On Wed, Dec 01, 2021 at 01:49:09PM +0000, Marc Zyngier wrote:
> > > > > > + state = read_sysreg_s(SYS_IMP_APL_PMCR0_EL1);
> > > > > > + overflow = read_sysreg_s(SYS_IMP_APL_PMSR_EL1);
> > > > >
> > > > > I assume the overflow behaviour is free-running rather than stopping?
> > > >
> > > > Configurable, apparently. At the moment, I set it to stop on overflow.
> > > > Happy to change the behaviour though.
> > >
> > > The architected PMU continues counting upon overflow (which prevents
> > > losing counts around the overlflow occurring), so I'd prefer that.
> > >
> > > Is that behaviour per-counter, or for the PMU as a whole?
> >
> > It is global. This will probably require some additional rework to
> > clear bit 47 in overflowing counters, which we can't do atomically.
>
> Ah; I see.
>
> To calrify my comment above, the reason for wanting the counter to keep
> counting is to count during the window between the IRQ being asserted and the
> PMU IRQ handler being invoked, and it's fine for there to be a blackout period
> *within* the PMU IRQ handler.
>
> So for example it would be fine to have:
>
> irq_handler()
> {
> if (!any_counter_overflowed())
> return IRQ_NONE;
>
> stop_all_counters();
>
> for_each_counter(c) {
> handle_counter(c);
> }
>
> start_all_counters();
>
> return IRQ_HANDLED;
>
> }
>
> ... and I think with that the regular per-counter period
> reprogramming would do the right thing?
Yup. It looks like this works just fine.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
prev parent reply other threads:[~2021-12-03 16:22 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-01 13:49 [PATCH v2 0/8] drivers/perf: CPU PMU driver for Apple M1 Marc Zyngier
2021-12-01 13:49 ` [PATCH v2 1/8] dt-bindings: arm-pmu: Document Apple PMU compatible strings Marc Zyngier
2021-12-12 7:27 ` Hector Martin
2021-12-01 13:49 ` [PATCH v2 2/8] dt-bindings: apple,aic: Add CPU PMU per-cpu pseudo-interrupts Marc Zyngier
2021-12-12 7:26 ` Hector Martin
2021-12-01 13:49 ` [PATCH v2 3/8] irqchip/apple-aic: Add cpumasks for E and P cores Marc Zyngier
2021-12-01 16:08 ` Mark Rutland
2021-12-03 16:32 ` Marc Zyngier
2021-12-12 7:22 ` Hector Martin
2021-12-12 7:30 ` Hector Martin
2021-12-13 14:43 ` Marc Zyngier
2021-12-01 13:49 ` [PATCH v2 4/8] irqchip/apple-aic: Wire PMU interrupts Marc Zyngier
2021-12-12 7:25 ` Hector Martin
2021-12-01 13:49 ` [PATCH v2 5/8] irqchip/apple-aic: Move PMU-specific registers to their own include file Marc Zyngier
2021-12-12 7:23 ` Hector Martin
2021-12-01 13:49 ` [PATCH v2 6/8] arm64: apple: t8301: Add PMU nodes Marc Zyngier
2021-12-12 7:26 ` Hector Martin
2021-12-01 13:49 ` [PATCH v2 7/8] drivers/perf: arm_pmu: Handle 47 bit counters Marc Zyngier
2021-12-12 7:26 ` Hector Martin
2021-12-01 13:49 ` [PATCH v2 8/8] drivers/perf: Add Apple icestorm/firestorm CPU PMU driver Marc Zyngier
2021-12-01 16:58 ` Mark Rutland
2021-12-01 17:56 ` Alyssa Rosenzweig
2021-12-02 15:39 ` Marc Zyngier
2021-12-02 16:14 ` Mark Rutland
2021-12-03 11:22 ` Marc Zyngier
2021-12-03 12:04 ` Mark Rutland
2021-12-03 16:22 ` Marc Zyngier [this message]
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