From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5B07C7EE24 for ; Tue, 6 Jun 2023 10:43:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237022AbjFFKns (ORCPT ); Tue, 6 Jun 2023 06:43:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60148 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237297AbjFFKmm (ORCPT ); Tue, 6 Jun 2023 06:42:42 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E15EA1BEA; Tue, 6 Jun 2023 03:41:24 -0700 (PDT) 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 E68562F4; Tue, 6 Jun 2023 03:42:09 -0700 (PDT) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.28.175]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 95E553F587; Tue, 6 Jun 2023 03:41:22 -0700 (PDT) Date: Tue, 6 Jun 2023 11:41:17 +0100 From: Mark Rutland To: Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, Mark Brown , James Clark , Rob Herring , Marc Zyngier , Suzuki Poulose , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , linux-perf-users@vger.kernel.org Subject: Re: [PATCH V11 05/10] arm64/perf: Add branch stack support in ARMV8 PMU Message-ID: References: <20230531040428.501523-1-anshuman.khandual@arm.com> <20230531040428.501523-6-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 06, 2023 at 04:04:25PM +0530, Anshuman Khandual wrote: > On 6/5/23 17:35, Mark Rutland wrote: > > On Wed, May 31, 2023 at 09:34:23AM +0530, Anshuman Khandual wrote: > >> static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu) > >> @@ -1145,12 +1162,24 @@ static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu) > >> }; > >> int ret; > >> > >> + ret = armv8pmu_private_alloc(cpu_pmu); > >> + if (ret) > >> + return ret; > >> + > >> ret = smp_call_function_any(&cpu_pmu->supported_cpus, > >> __armv8pmu_probe_pmu, > >> &probe, 1); > >> if (ret) > >> return ret; > >> > >> + if (arm_pmu_branch_stack_supported(cpu_pmu)) { > >> + ret = branch_records_alloc(cpu_pmu); > >> + if (ret) > >> + return ret; > >> + } else { > >> + armv8pmu_private_free(cpu_pmu); > >> + } > > > > I see from the next patch that "private" is four ints, so please just add that > > to struct arm_pmu under an ifdef CONFIG_ARM64_BRBE. That'll simplify this, and > > if we end up needing more space in future we can consider factoring it out. > > struct arm_pmu { > ........................................ > /* Implementation specific attributes */ > void *private; > } > > private pointer here creates an abstraction for given pmu implementation > to hide attribute details without making it known to core arm pmu layer. > Although adding ifdef CONFIG_ARM64_BRBE solves the problem as mentioned > above, it does break that abstraction. Currently arm_pmu layer is aware > about 'branch records' but not about BRBE in particular which the driver > adds later on. I suggest we should not break that abstraction. I understand the rationale, but I think it's simpler for now to break that abstraction. We can always refactor it later. > Instead a global 'static struct brbe_hw_attr' in drivers/perf/arm_brbe.c > can be initialized into arm_pmu->private during armv8pmu_branch_probe(), > which will also solve the allocation-free problem. IIUC that's not going to work for big.LITTLE systems where the BRBE support varies, as we need this data per arm_pmu. > Also similar helpers armv8pmu_task_ctx_alloc()/free() could be defined to > manage task context cache i.e arm_pmu->pmu.task_ctx_cache independently. > > But now armv8pmu_task_ctx_alloc() can be called after pmu probe confirms > to have arm_pmu->has_branch_stack. I think those are different, and should be kept. Thanks, Mark.