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 773F92EB5D7; Fri, 27 Jun 2025 17:57:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751047059; cv=none; b=dyhoKr662fE0h2G55KcZE+LK/diJFi8zg/OaXWyrwELcHtUKFvt9TbRNUnT4VQco4UszhiNGpfhFtoMlWLlqLkg2/1CIk66bVpk1Bfu577LXeYn4xjkVqAXGBUlmiW2Wt/AWzwimY4MqIMkDlr5DFEQFtOZGPFO/QfWX7LQodnI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751047059; c=relaxed/simple; bh=lO/D+8l/3CtfDrZf5ur943JGKj+bthfoO2Ff354hWFY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=paXGcOcDEtfmQPvqwViUY9Jb+NVOEaoU5UYpxq1aj+9+kXZOm0jbaBaXYAy9FFW5JhmeSrgduAmdBCjsOsUE+CiRNTxn9EwVDJ+u0O89OAJQHf26MCIBQfVD7SKcfUExmnuam/ZcEit03UV33q/kWDeU6wXKgZzzARj2txFRri8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 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 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 951701655; Fri, 27 Jun 2025 10:57:18 -0700 (PDT) Received: from [10.1.196.50] (e121345-lin.cambridge.arm.com [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B10163F58B; Fri, 27 Jun 2025 10:57:33 -0700 (PDT) Message-ID: <39117e6a-ebb6-4c92-a19c-2033c4e590cd@arm.com> Date: Fri, 27 Jun 2025 18:57:31 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] perf/arm-cmn: reduce stack usage in arm_cmn_probe() To: Arnd Bergmann , Will Deacon , Mark Rutland , Nathan Chancellor Cc: Arnd Bergmann , Nick Desaulniers , Bill Wendling , Justin Stitt , Ilkka Koskinen , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev References: <20250620115149.132845-1-arnd@kernel.org> From: Robin Murphy Content-Language: en-GB In-Reply-To: <20250620115149.132845-1-arnd@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 20/06/2025 12:51 pm, Arnd Bergmann wrote: > From: Arnd Bergmann > > This function has a rather large stack usage, which triggers the > warning limit with clang if I reduce the default to 1280 bytes: > > drivers/perf/arm-cmn.c:2541:12: error: stack frame size (1312) exceeds limit (1280) in 'arm_cmn_probe' [-Werror,-Wframe-larger-than] > > This is a combination of two problems: > > - The arm_cmn_discover() function has some large local variables and > gets inlined here by clang (but not gcc) > > - The (struct pmu) assignment adds an extra copy of the pmu structure > on the stack and does a memcpy() from that > > Address the first one here by marking arm_cmn_discover() as noinline_for_stack, > making clang behave more like gcc here. This gets it under the warning > limit, though the total stack usage does not actually get reduced. At that point, though, it seems like we may as well just disable the warning :/ Fortunately it's not actually that hard to improve matters here, so I've just sent that patch: https://lore.kernel.org/r/e7dd41bf0f1b098e2e4b01ef91318a4b272abff8.1751046159.git.robin.murphy@arm.com/T/#u > It would be nice to also change the way struct pmu is initialized, but I > see that this is done consistently for all pmu drivers. Ideally the function > pointers should be moved into a 'static const' structure per driver as this > is done in most other subsystems. Beware that perf_pmu_register() does some further dynamic assignment of callbacks based on what the driver provided, so it's not necessarily straightforward to change in struct pmu itself. However, FWIW I have recently been playing with some ideas for reducing the amount of PMU registration boilerplate, and indeed one of them is to have a driver-level static template passed to a registration helper, which would at least make it easy to avoid the full by-value copies everywhere. Thanks, Robin. > > Signed-off-by: Arnd Bergmann > --- > drivers/perf/arm-cmn.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c > index 031d45d0fe3d..430c89760391 100644 > --- a/drivers/perf/arm-cmn.c > +++ b/drivers/perf/arm-cmn.c > @@ -2243,7 +2243,8 @@ static enum cmn_node_type arm_cmn_subtype(enum cmn_node_type type) > } > } > > -static int arm_cmn_discover(struct arm_cmn *cmn, unsigned int rgn_offset) > +static noinline_for_stack int arm_cmn_discover(struct arm_cmn *cmn, > + unsigned int rgn_offset) > { > void __iomem *cfg_region; > struct arm_cmn_node cfg, *dn;