From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932802AbcHKQiA (ORCPT ); Thu, 11 Aug 2016 12:38:00 -0400 Received: from foss.arm.com ([217.140.101.70]:55344 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932694AbcHKQgT (ORCPT ); Thu, 11 Aug 2016 12:36:19 -0400 From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: acme@kernel.org, adrian.hunter@intel.com, alexander.shishkin@linux.intel.com, hekuang@huawei.com, jolsa@kernel.org, mark.rutland@arm.com, mingo@redhat.com, peterz@infradead.org, wangnan0@huawei.com Subject: [RFCv3 2/2] perf: util: support sysfs supported_cpumask file Date: Thu, 11 Aug 2016 17:36:06 +0100 Message-Id: <1470933366-1364-3-git-send-email-mark.rutland@arm.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1470933366-1364-1-git-send-email-mark.rutland@arm.com> References: <1470933366-1364-1-git-send-email-mark.rutland@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The perf tools can read a cpumask file for a PMU, describing a subset of CPUs which that PMU covers. So far this has only been used to cater for uncore PMUs, which in practice happen to only have a single CPU described in the mask. Until recently, the perf tools only correctly handled cpumask containing a single CPU, and only when monitoring in system-wide mode. For example, prior to commit 00e727bb389359c8 ("perf stat: Balance opening and reading events"), a mask with more than a single CPU could cause perf stat to hang. When a CPU PMU covers a subset of CPUs, but lacks a cpumask, perf record will fail to open events (on the cores the PMU does not support), and gives up. For systems with heterogeneous CPUs such as ARM big.LITTLE systems, this presents a problem. We have a PMU for each microarchitecture (e.g. a big PMU and a little PMU), and would like to expose a cpumask for each (so as to allow perf record and other tools to do the right thing). However, doing so kernel-side will cause old perf binaries to not function (e.g. hitting the issue solved by 00e727bb389359c8), and thus commits the cardinal sin of breaking (existing) userspace. To address this chicken-and-egg problem, this patch adds support got a new file, supported_cpumask, which is largely identical to the existing cpumask file. A kernel can expose this file, knowing that new perf binaries will correctly support it, while old perf binaries will not look for it (and thus will not be broken). Signed-off-by: Mark Rutland --- tools/perf/util/pmu.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c index ddb0261..ded0cb2 100644 --- a/tools/perf/util/pmu.c +++ b/tools/perf/util/pmu.c @@ -445,14 +445,23 @@ static struct cpu_map *pmu_cpumask(const char *name) FILE *file; struct cpu_map *cpus; const char *sysfs = sysfs__mountpoint(); + const char *templates[] = { + "%s/bus/event_source/devices/%s/cpumask", + "%s/bus/event_source/devices/%s/supported_cpumask", + NULL + }; + const char **template; if (!sysfs) return NULL; - snprintf(path, PATH_MAX, - "%s/bus/event_source/devices/%s/cpumask", sysfs, name); + for (template = templates; *template; template++) { + snprintf(path, PATH_MAX, *template, sysfs, name); + if (stat(path, &st) == 0) + break; + } - if (stat(path, &st) < 0) + if (!*template) return NULL; file = fopen(path, "r"); -- 1.9.1