From ea2ee83c9247d94f466e532906bb16ae37e4657b Mon Sep 17 00:00:00 2001 From: Raghavendra Rao Ananta Date: Fri, 19 Oct 2018 10:06:28 -0700 Subject: [PATCH] perf: Cancel the mux hrtimer during CPU hotplug to avoid migration The current design of hrtimers migrates the pinned timers to a different CPU upon its hotplug. However, perf-core needs to maintain the mux-hrtimers on a per CPU basis. That is, each hrtimer carries the context for that particular CPU and would lose this context if it gets migrated to a different CPU. As a result, cancel the hrtimer for the CPU that's about to go down and restart it (if required) when the perf-events are being created. Change-Id: I7a1d0456208855e3a99a7d49e59c6dae811d146e Signed-off-by: Raghavendra Rao Ananta [mojha@codeaurora.org: Resolved merge conflict and added missing `cpuctx` variable to avoid build failure] Signed-off-by: Mukesh Ojha --- include/linux/perf_event.h | 2 +- kernel/events/core.c | 15 ++++++++++++++- 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index f501b8c0de4e..efce166a9f17 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -231,7 +231,7 @@ struct pmu { int capabilities; int * __percpu pmu_disable_count; - struct perf_cpu_context * __percpu pmu_cpu_context; + struct perf_cpu_context __percpu *pmu_cpu_context; atomic_t exclusive_cnt; /* < 0: cpu; > 0: tsk */ int task_ctx_nr; int hrtimer_interval_ms; diff --git a/kernel/events/core.c b/kernel/events/core.c index a8f984b4fcff..3e6e5eb3e4d2 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9654,13 +9654,26 @@ static void __perf_event_stop_swclock(void *__info) static void perf_event_exit_cpu_context(int cpu) { + struct perf_cpu_context *cpuctx; struct perf_event_context *ctx; + unsigned long flags; struct pmu *pmu; int idx; idx = srcu_read_lock(&pmus_srcu); list_for_each_entry_rcu(pmu, &pmus, entry) { - ctx = &per_cpu_ptr(pmu->pmu_cpu_context, cpu)->ctx; + cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu); + ctx = &cpuctx->ctx; + + /* Cancel the mux hrtimer to avoid CPU migration */ + if (pmu->task_ctx_nr != perf_sw_context) { + raw_spin_lock_irqsave(&cpuctx->hrtimer_lock, flags); + hrtimer_cancel(&cpuctx->hrtimer); + cpuctx->hrtimer_active = 0; + raw_spin_unlock_irqrestore(&cpuctx->hrtimer_lock, + flags); + } + mutex_lock(&ctx->mutex); /* * If keeping events across hotplugging is supported, do not