perf pmu: Add CPU map for "cpu" PMUs

A typical "cpu" PMU has no "cpus" or "cpumask" file meaning the CPU
map is set to NULL, which also encodes an empty CPU map. Update
pmu_cpumask so that if the "cpu" PMU fails to load a CPU map, use a
default of all online PMUs.

Remove const from cpu_map__online for the sake of reference counting.
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ali Saidi <alisaidi@amazon.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Dmitrii Dolgov <9erthalion6@gmail.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kang Minchul <tegongkang@gmail.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Ming Wang <wangming01@loongson.cn>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20230527072210.2900565-8-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/cpumap.c

@@ -667,9 +667,9 @@ size_t cpu_map__snprint_mask(struct perf_cpu_map *map, char *buf, size_t size)
 	return ptr - buf;
 }
 
-const struct perf_cpu_map *cpu_map__online(void) /* thread unsafe */
+struct perf_cpu_map *cpu_map__online(void) /* thread unsafe */
 {
-	static const struct perf_cpu_map *online = NULL;
+	static struct perf_cpu_map *online;
 
 	if (!online)
 		online = perf_cpu_map__new(NULL); /* from /sys/devices/system/cpu/online */

tools/perf/util/cpumap.h

@@ -55,7 +55,7 @@ struct perf_cpu_map *cpu_map__new_data(const struct perf_record_cpu_map_data *da
 size_t cpu_map__snprint(struct perf_cpu_map *map, char *buf, size_t size);
 size_t cpu_map__snprint_mask(struct perf_cpu_map *map, char *buf, size_t size);
 size_t cpu_map__fprintf(struct perf_cpu_map *map, FILE *fp);
-const struct perf_cpu_map *cpu_map__online(void); /* thread unsafe */
+struct perf_cpu_map *cpu_map__online(void); /* thread unsafe */
 
 int cpu__setup_cpunode_map(void);
 
@@ -66,7 +66,7 @@ struct perf_cpu cpu__max_present_cpu(void);
 /**
  * cpu_map__is_dummy - Events associated with a pid, rather than a CPU, use a single dummy map with an entry of -1.
  */
-static inline bool cpu_map__is_dummy(struct perf_cpu_map *cpus)
+static inline bool cpu_map__is_dummy(const struct perf_cpu_map *cpus)
 {
 	return perf_cpu_map__nr(cpus) == 1 && perf_cpu_map__cpu(cpus, 0).cpu == -1;
 }

tools/perf/util/pmu.c

@@ -610,7 +610,7 @@ static struct perf_cpu_map *pmu_cpumask(int dirfd, const char *name)
 			return cpus;
 	}
 
-	return NULL;
+	return !strcmp(name, "cpu") ? perf_cpu_map__get(cpu_map__online()) : NULL;
 }
 
 static bool pmu_is_uncore(int dirfd, const char *name)