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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2B5CBCA0FF2 for ; Tue, 26 Aug 2025 16:35:26 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id B1B8910E395; Tue, 26 Aug 2025 16:35:25 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id 7D3E010E395; Tue, 26 Aug 2025 16:35:24 +0000 (UTC) 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 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 X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" 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.