From 5101ef20f0ef1de79091a1fdb6b1a7f07565545a Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Tue, 26 Apr 2016 11:33:46 +0100 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Catalin Marinas Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: Will Deacon Cc: linux-arm-kernel@lists.infradead.org Link: http://lkml.kernel.org/r/20160426103346.GA20836@leverpostej Signed-off-by: Ingo Molnar --- drivers/perf/arm_pmu.c | 8 ++++++++ include/linux/perf_event.h | 1 + kernel/events/core.c | 8 +++++++- 3 files changed, 16 insertions(+), 1 deletion(-) 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 @@ 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: diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index c77e4a1..9e1c3ad 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -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 diff --git a/kernel/events/core.c b/kernel/events/core.c index 63be654..fc0290f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8443,7 +8443,13 @@ skip_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; -- 2.7.4