From 6a02ad66b2c44155d529f430d4fa5c6c66321077 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 3 Feb 2014 18:11:08 +0100 Subject: [PATCH] perf/x86: Push the duration-logging printk() to IRQ context Calling printk() from NMI context is bad (TM), so move it to IRQ context. This also avoids the problem where the printk() time is measured by the generic NMI duration goo and triggers a second warning. Signed-off-by: Peter Zijlstra Cc: Don Zickus Cc: Dave Hansen Link: http://lkml.kernel.org/n/tip-75dv35xf6dhhmeb7nq6fua31@git.kernel.org Signed-off-by: Ingo Molnar --- include/linux/irq_work.h | 2 ++ kernel/events/core.c | 28 +++++++++++++++++++++------- 2 files changed, 23 insertions(+), 7 deletions(-) diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h index 66017028dcb3..add13c8624b7 100644 --- a/include/linux/irq_work.h +++ b/include/linux/irq_work.h @@ -30,6 +30,8 @@ void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *)) work->func = func; } +#define DEFINE_IRQ_WORK(name, _f) struct irq_work name = { .func = (_f), } + void irq_work_queue(struct irq_work *work); void irq_work_run(void); void irq_work_sync(struct irq_work *work); diff --git a/kernel/events/core.c b/kernel/events/core.c index 56003c6edfd3..2067cbb378eb 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -231,11 +231,29 @@ int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write, #define NR_ACCUMULATED_SAMPLES 128 static DEFINE_PER_CPU(u64, running_sample_length); -void perf_sample_event_took(u64 sample_len_ns) +static void perf_duration_warn(struct irq_work *w) { + u64 allowed_ns = ACCESS_ONCE(perf_sample_allowed_ns); u64 avg_local_sample_len; u64 local_samples_len; + + local_samples_len = __get_cpu_var(running_sample_length); + avg_local_sample_len = local_samples_len/NR_ACCUMULATED_SAMPLES; + + printk_ratelimited(KERN_WARNING + "perf interrupt took too long (%lld > %lld), lowering " + "kernel.perf_event_max_sample_rate to %d\n", + avg_local_sample_len, allowed_ns, + sysctl_perf_event_sample_rate); +} + +static DEFINE_IRQ_WORK(perf_duration_work, perf_duration_warn); + +void perf_sample_event_took(u64 sample_len_ns) +{ u64 allowed_ns = ACCESS_ONCE(perf_sample_allowed_ns); + u64 avg_local_sample_len; + u64 local_samples_len; if (allowed_ns == 0) return; @@ -263,13 +281,9 @@ void perf_sample_event_took(u64 sample_len_ns) sysctl_perf_event_sample_rate = max_samples_per_tick * HZ; perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate; - printk_ratelimited(KERN_WARNING - "perf samples too long (%lld > %lld), lowering " - "kernel.perf_event_max_sample_rate to %d\n", - avg_local_sample_len, allowed_ns, - sysctl_perf_event_sample_rate); - update_perf_cpu_limits(); + + irq_work_queue(&perf_duration_work); } static atomic64_t perf_event_id; -- 2.20.1