From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C6BDE154AB for ; Tue, 21 Nov 2023 15:56:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C9E20FEC; Tue, 21 Nov 2023 07:57:12 -0800 (PST) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.34.196]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D785A3F6C4; Tue, 21 Nov 2023 07:56:24 -0800 (PST) Date: Tue, 21 Nov 2023 15:56:22 +0000 From: Mark Rutland To: Ian Rogers Cc: Marc Zyngier , Hector Martin , Arnaldo Carvalho de Melo , James Clark , linux-perf-users@vger.kernel.org, LKML , Asahi Linux Subject: Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since v6.5 Message-ID: References: <08f1f185-e259-4014-9ca4-6411d5c1bc65@marcan.st> <86pm03z0kw.wl-maz@kernel.org> <86o7fnyvrq.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: asahi@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Nov 21, 2023 at 07:41:17AM -0800, Ian Rogers wrote: > Hi Marc, Hi Ian, > I'm unclear if you are running a newer perf tool on an older kernel or > not. In any case I'll assume the kernel and perf tool versions match. > In Linux 6.6 this patch was added to the ARM PMU: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/perf/arm_pmu.c?id=5c816728651ae425954542fed64d21d40cb75a9f > > My guess is that the apple_icestorm_pmu requires a similar patch. The apple_icestorm_pmu PMU driver uses the arm_pmu framework, so it's using that code (since v6.6). > The perf tool is supposed to not use extended types when they aren't > supported: > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmus.c?h=perf-tools-next#n532 How does that is_event_supported() check actually work? I suspect that's giving the wrong answer. Regardless, I think the tool is doing something semantically wrong, see below. > So I share your confusion as to why something broke. > > PERF_TYPE_HARDWARE is a legacy type where there are hardcoded type and > config values that correspond to an event. The PMU driver turns legacy > events into the real types. On BIG.little systems if the legacy events > are monitoring a task a different event is needed for each PMU (ie >1 > event). In your example you are monitoring 'ls', a task, and so > different cycles events are necessary. In the high 32-bits (the > extended type) the PMU is identified. I think the interesting thing here is that the tool is mapping events with an explicit PMU into legacy PERF_TYPE_HARDWARE events, which is the opposite direction than intended. Regardless of whether PERF_TYPE_HARDWARE events can be targetted to a specific PMU, if the user has requested to use a specific PMU we should be using that PMU and related event namespace. Marc's command line was: sudo taskset -c 0 ./perf stat -vvv \ -e apple_icestorm_pmu/cycles/ \ -e apple_firestorm_pmu/cycles/ \ -e cycles \ ls ... and so the apple_*_pmu events should target their respective PMUs, and the plain 'cycles' event could legitimately be opened as a single PERF_TYPE_HARDWARE event, or split into two directed PERF_TYPE_HARDWARE events targetting the two PMUs. However, thwe tool opens three (undirected?) PERF_TYPE_HARDWARE events: Opening: apple_icestorm_pmu/cycles/ ------------------------------------------------------------ perf_event_attr: type 0 (PERF_TYPE_HARDWARE) size 136 config 0 (PERF_COUNT_HW_CPU_CYCLES) sample_type IDENTIFIER read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING disabled 1 inherit 1 enable_on_exec 1 exclude_guest 1 ------------------------------------------------------------ sys_perf_event_open: pid 1045843 cpu -1 group_fd -1 flags 0x8 = 3 Opening: apple_firestorm_pmu/cycles/ ------------------------------------------------------------ perf_event_attr: type 0 (PERF_TYPE_HARDWARE) size 136 config 0 (PERF_COUNT_HW_CPU_CYCLES) sample_type IDENTIFIER read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING disabled 1 inherit 1 enable_on_exec 1 exclude_guest 1 ------------------------------------------------------------ sys_perf_event_open: pid 1045843 cpu -1 group_fd -1 flags 0x8 = 4 Opening: cycles ------------------------------------------------------------ perf_event_attr: type 0 (PERF_TYPE_HARDWARE) size 136 config 0 (PERF_COUNT_HW_CPU_CYCLES) sample_type IDENTIFIER read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING disabled 1 inherit 1 enable_on_exec 1 exclude_guest 1 ------------------------------------------------------------ Mark.