From 7e3fcffe955440101493cd8f32f75840ddf87b6f Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 8 Sep 2016 11:21:52 +0100 Subject: [PATCH] perf pmu: Support alternative sysfs cpumask 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, cpus, 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 Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Mark Rutland Cc: Peter Zijlstra Cc: Will Deacon Link: http://lkml.kernel.org/r/1473330112-28528-8-git-send-email-mark.rutland@arm.com Signed-off-by: Arnaldo Carvalho de Melo --- 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 ddb0261b2577..2babcdf62839 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/cpus", + 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"); -- 2.45.2