Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 5101ef20 authored by Mark Rutland's avatar Mark Rutland Committed by Ingo Molnar
Browse files

perf/arm: Special-case hetereogeneous CPUs 



Commit:

  26657848 ("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:

  66eb579e ("perf: allow for PMU-specific event filtering")
  c904e32a ("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: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 6e855cd4

drivers/perf/arm_pmu.c

+8 −0
Original line number Diff line number Diff line
@@ -847,6 +847,14 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu) 
	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:

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -225,6 +225,7 @@ struct perf_event; 
#define PERF_PMU_CAP_AUX_SW_DOUBLEBUF		0x08

#define PERF_PMU_CAP_EXCLUSIVE			0x10

#define PERF_PMU_CAP_ITRACE			0x20

#define PERF_PMU_CAP_HETEROGENEOUS_CPUS		0x40



/**

 * struct pmu - generic performance monitoring unit

kernel/events/core.c

+7 −1
Original line number Diff line number Diff line
@@ -8443,7 +8443,13 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type) 
	if (pmu->task_ctx_nr == perf_hw_context) {

		static int hw_context_taken = 0;



		if (WARN_ON_ONCE(hw_context_taken))

		/*

		 * Other than systems with heterogeneous CPUs, it never makes

		 * sense for two PMUs to share perf_hw_context. PMUs which are

		 * uncore must use perf_invalid_context.

		 */

		if (WARN_ON_ONCE(hw_context_taken &&

		    !(pmu->capabilities & PERF_PMU_CAP_HETEROGENEOUS_CPUS)))

			pmu->task_ctx_nr = perf_invalid_context;



		hw_context_taken = 1;