From: Mark Rutland <mark.rutl...@arm.com>
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 <mark.rutl...@arm.com>
Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
Cc: Jiri Olsa <jo...@kernel.org>
Cc: Mark Rutland <mark.rutl...@arm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Will Deacon <will.dea...@arm.com>
Link:
http://lkml.kernel.org/r/1473330112-28528-8-git-send-email-mark.rutl...@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <a...@redhat.com>
---
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");
--
2.7.4
