From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH] arm64: dts: allwinner: a64: Drop PMU node Date: Tue, 6 Aug 2019 22:14:39 +0100 Message-ID: <36e60078-7dd5-9c07-ffa1-6092d8c70fa8@arm.com> References: <20190806140135.4739-1-anarsoul@gmail.com> <89402d22-d432-9551-e787-c8ede16dbe5f@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-GB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Vasily Khoruzhick , Harald Geyer Cc: Mark Rutland , devicetree , "Jared D . McNeill" , Maxime Ripard , Chen-Yu Tsai , Rob Herring , arm-linux List-Id: devicetree@vger.kernel.org On 2019-08-06 9:52 pm, Vasily Khoruzhick wrote: > On Tue, Aug 6, 2019 at 1:19 PM Harald Geyer wrote: >> >> Vasily Khoruzhick writes: >>> On Tue, Aug 6, 2019 at 7:35 AM Robin Murphy 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. Robin.