perf/arm: Special-case hetereogeneous CPUs
Commit:
26657848502b7847 ("perf/core: Verify we have a single perf_hw_context PMU")
forcefully prevents multiple PMUs from sharing perf_hw_context, as this
generally doesn't make sense. It is a common bug for uncore PMUs to
use perf_hw_context rather than perf_invalid_context, which this detects.
However, systems exist with heterogeneous CPUs (and hence heterogeneous
HW PMUs), for which sharing perf_hw_context is necessary, and possible
in some limited cases.
To make this work we have to perform some gymnastics, as we did in these
commits:
66eb579e66ecfea5 ("perf: allow for PMU-specific event filtering")
c904e32a69b7c779 ("arm: perf: filter unschedulable events")
To allow those systems to work, we must allow PMUs for heterogeneous
CPUs to share perf_hw_context, though we must still disallow sharing
otherwise to detect the common misuse of perf_hw_context.
This patch adds a new PERF_PMU_CAP_HETEROGENEOUS_CPUS for this, updates
the core logic to account for this, and makes use of it in the arm_pmu
code that is used for systems with heterogeneous CPUs. Comments are
added to make the rationale clear and hopefully avoid accidental abuse.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20160426103346.GA20836@leverpostej
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index f700908..f2d01d4d9 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -847,6 +847,14 @@
if (!platform_get_irq(cpu_pmu->plat_device, 0))
cpu_pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
+ /*
+ * This is a CPU PMU potentially in a heterogeneous configuration (e.g.
+ * big.LITTLE). This is not an uncore PMU, and we have taken ctx
+ * sharing into account (e.g. with our pmu::filter_match callback and
+ * pmu::event_init group validation).
+ */
+ cpu_pmu->pmu.capabilities |= PERF_PMU_CAP_HETEROGENEOUS_CPUS;
+
return 0;
out_unregister: