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 63FBE31A543; Tue, 26 Aug 2025 15:54:03 +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=1756223645; cv=none; b=J/2CPhY4He/SzlWTiTlf83dasJTNnjunKYC2L1d+UNv8vIk3HnT9ewQGCsY9DcE71JgoOj8elB3aNI+bFuGC6k8AXhCfqnsxby8EcyEUBBhKzxtDXMCZxioLi58xKUBHj8jpH1NEC1DUTO/sCGEsBCKS0sJhAlFp4oGJnVi1pFY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756223645; c=relaxed/simple; bh=kYW541e1nFWGVYhRgbZq3mXAqdUof67Phlv3fCn/KoY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EkLRDon0xYOr1aP66fjkt/S49LOKgB1KVTGSN5jkK54BbU6yZuxa7bTvXETc/p6kJCg8O4i07gXFR1dje7ZqfMFy6qrXgRy4yXMuzeIDczbXfFJIYQbdTafr2tyb+bw6ykbWNz8aFQ+XquhkKSb/sYqY8g86TeXzwubfTxMmWf4= 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 39F0B1A25; Tue, 26 Aug 2025 08:53:54 -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 8041A3F694; Tue, 26 Aug 2025 08:53:54 -0700 (PDT) Message-ID: <983df32a-ba74-421d-bc20-06e778b4d2c9@arm.com> Date: Tue, 26 Aug 2025 16:53:51 +0100 Precedence: bulk X-Mailing-List: imx@lists.linux.dev 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: Leo Yan Cc: peterz@infradead.org, mingo@redhat.com, will@kernel.org, mark.rutland@arm.com, 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: <20250826131124.GB745921@e132581.arm.com> From: Robin Murphy Content-Language: en-GB In-Reply-To: <20250826131124.GB745921@e132581.arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025-08-26 2:11 pm, Leo Yan 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/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c >> index 369e77ad5f13..dbd52851f5c6 100644 >> --- a/drivers/perf/arm_spe_pmu.c >> +++ b/drivers/perf/arm_spe_pmu.c >> @@ -955,7 +955,8 @@ static int arm_spe_pmu_perf_init(struct arm_spe_pmu *spe_pmu) >> spe_pmu->pmu = (struct pmu) { >> .module = THIS_MODULE, >> .parent = &spe_pmu->pdev->dev, >> - .capabilities = PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE, >> + .capabilities = PERF_PMU_CAP_SAMPLING | >> + PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE, >> .attr_groups = arm_spe_pmu_attr_groups, >> /* >> * We hitch a ride on the software context here, so that > > The change in Arm SPE driver looks good to me. > > I noticed you did not set the flag for other AUX events, like Arm > CoreSight, Intel PT and bts. The drivers locate in: > > drivers/hwtracing/coresight/coresight-etm-perf.c > arch/x86/events/intel/bts.c > arch/x86/events/intel/pt.c > > Genearlly, AUX events generate interrupts based on AUX ring buffer > watermark but not the period. Seems to me, it is correct to set the > PERF_PMU_CAP_SAMPLING flag for them. This cap is given to drivers which handle event->attr.sample_period and call perf_event_overflow() - or in a few rare cases, perf_output_sample() directly - to do something meaningful with it, since the intent is to convey "I properly handle events for which is_sampling_event() is true". My understanding is that aux events are something else entirely, but I'm happy to be corrected. Otherwise, perhaps this suggests it deserves to be named a little more specifically for clarity, maybe PERF_CAP_SAMPLING_EVENTS? Thanks, Robin. > A special case is Arm CoreSight legacy sinks (like ETR/ETB, etc) > don't has interrupt. We might need set or clear the flag on the fly > based on sink type: > > diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c > index f1551c08ecb2..404edc94c198 100644 > --- a/drivers/hwtracing/coresight/coresight-etm-perf.c > +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c > @@ -433,6 +433,11 @@ static void *etm_setup_aux(struct perf_event *event, void **pages, > if (!sink) > goto err; > > + if (coresight_is_percpu_sink(sink)) > + event->pmu.capabilities = PERF_PMU_CAP_SAMPLING; > + else > + event->pmu.capabilities &= ~PERF_PMU_CAP_SAMPLING; > + > > Thanks, > Leo