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 984B5362078; Tue, 26 Aug 2025 16:35:24 +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=1756226126; cv=none; b=WzpnlZGTV8MbtXNa1m3NS8QdCm/56MDcgWoMYggcCn3KExtxnEgZlrfI7C/hKw/GJkCI62Kfmmaz+3969AMx6CAStR10r5Ang1YXoYg5CzbnClXA26HyHkSDg2WxxQFjXE4dSpV5QxYBH/m+MkAFecXlBAsULiwB3Ym7TUHscns= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756226126; c=relaxed/simple; bh=Qr2qTi+512p+e4SYLAIsyC00OV8S61hM2BP79hz1vL4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=RTnm4y7h5ZZ/UTvzOdkB5oxEB9mFnSoMaZOUaAC+YHOneg6tbAG/4vKqRoYuNWYP1XBSdhL98+tRjMJ62MELogaQz2m9KkQzdPQfi3hfj3UovIXRRcdnzzAtUayna3VLzimij34HlQwmgWMT6WH3FxGh5D/QevhHJho1AQiMA2E= 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 8E4571A25; Tue, 26 Aug 2025 09:35:15 -0700 (PDT) Received: from [10.57.4.86] (unknown [10.57.4.86]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A5A1B3F694; Tue, 26 Aug 2025 09:35:17 -0700 (PDT) Message-ID: <8d6ac059-fc8f-4a5d-b49e-d02777c01cfb@arm.com> Date: Tue, 26 Aug 2025 17:35:15 +0100 Precedence: bulk X-Mailing-List: sparclinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 16/19] perf: Introduce positive capability for sampling To: Mark Rutland , Peter Zijlstra Cc: mingo@redhat.com, will@kernel.org, acme@kernel.org, namhyung@kernel.org, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev, linux-csky@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-pm@vger.kernel.org, linux-rockchip@lists.infradead.org, dmaengine@vger.kernel.org, linux-fpga@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, coresight@lists.linaro.org, iommu@lists.linux.dev, linux-amlogic@lists.infradead.org, linux-cxl@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-riscv@lists.infradead.org References: <20250826130806.GY4067720@noisy.programming.kicks-ass.net> From: Robin Murphy Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025-08-26 2:28 pm, Mark Rutland wrote: > On Tue, Aug 26, 2025 at 03:08:06PM +0200, Peter Zijlstra wrote: >> On Wed, Aug 13, 2025 at 06:01:08PM +0100, Robin Murphy wrote: >>> Sampling is inherently a feature for CPU PMUs, given that the thing >>> to be sampled is a CPU context. These days, we have many more >>> uncore/system PMUs than CPU PMUs, so it no longer makes much sense to >>> assume sampling support by default and force the ever-growing majority >>> of drivers to opt out of it (or erroneously fail to). Instead, let's >>> introduce a positive opt-in capability that's more obvious and easier to >>> maintain. >> >>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h >>> index 4d439c24c901..bf2cfbeabba2 100644 >>> --- a/include/linux/perf_event.h >>> +++ b/include/linux/perf_event.h >>> @@ -294,7 +294,7 @@ struct perf_event_pmu_context; >>> /** >>> * pmu::capabilities flags >>> */ >>> -#define PERF_PMU_CAP_NO_INTERRUPT 0x0001 >>> +#define PERF_PMU_CAP_SAMPLING 0x0001 >>> #define PERF_PMU_CAP_NO_NMI 0x0002 >>> #define PERF_PMU_CAP_AUX_NO_SG 0x0004 >>> #define PERF_PMU_CAP_EXTENDED_REGS 0x0008 >>> @@ -305,6 +305,7 @@ struct perf_event_pmu_context; >>> #define PERF_PMU_CAP_EXTENDED_HW_TYPE 0x0100 >>> #define PERF_PMU_CAP_AUX_PAUSE 0x0200 >>> #define PERF_PMU_CAP_AUX_PREFER_LARGE 0x0400 >>> +#define PERF_PMU_CAP_NO_INTERRUPT 0x0800 >> >> So NO_INTERRUPT was supposed to be the negative of your new SAMPLING >> (and I agree with your reasoning). >> >> What I'm confused/curious about is why we retain NO_INTERRUPT? > > I see from your other reply that you spotted the next patch does that. > > For the sake of other reviewers or anyone digging through the git > history it's probably worth adding a line to this commit message to say: > > | A subsequent patch will remove PERF_PMU_CAP_NO_INTERRUPT as this > | requires some additional cleanup. Yup, the main reason is the set of drivers getting the new cap is smaller than the set of drivers currently not rejecting sampling events, so I wanted it to be clearly visible in the patch. Indeed I shall clarify the relationship to NO_INTERRUPT in the commit message. Thanks, Robin.