Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751933AbaBKPB3 (ORCPT ); Tue, 11 Feb 2014 10:01:29 -0500 Received: from merlin.infradead.org ([205.233.59.134]:57075 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751824AbaBKPB2 (ORCPT ); Tue, 11 Feb 2014 10:01:28 -0500 Date: Tue, 11 Feb 2014 16:01:16 +0100 From: Peter Zijlstra To: Dave Hansen Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, dzickus@redhat.com, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perf/core] x86/nmi: Push duration printk() to irq context Message-ID: <20140211150116.GO27965@twins.programming.kicks-ass.net> References: <52F9021C.1030801@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52F9021C.1030801@linux.intel.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 10, 2014 at 08:45:16AM -0800, Dave Hansen wrote: > The reason I coded this up was that NMIs were firing off so fast that > nothing else was getting a chance to run. With this patch, at least the > printk() would come out and I'd have some idea what was going on. How's something like this on top? It will start spewing to early_printk() (which is a lot nicer to use from NMI context too) when it fails to queue the IRQ-work because its already enqueued. It does have the false-positive for when two CPUs trigger the warn concurrently, but that should be rare and some extra clutter on the early printk shouldn't be a problem. --- include/linux/irq_work.h | 2 +- kernel/events/core.c | 9 +++++++-- kernel/irq_work.c | 6 ++++-- 3 files changed, 12 insertions(+), 5 deletions(-) diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h index add13c8..19ae05d 100644 --- a/include/linux/irq_work.h +++ b/include/linux/irq_work.h @@ -32,7 +32,7 @@ void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *)) #define DEFINE_IRQ_WORK(name, _f) struct irq_work name = { .func = (_f), } -void irq_work_queue(struct irq_work *work); +bool 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 2067cbb..45e5543 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -243,7 +243,7 @@ static void perf_duration_warn(struct irq_work *w) 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, + avg_local_sample_len, allowed_ns >> 1, sysctl_perf_event_sample_rate); } @@ -283,7 +283,12 @@ void perf_sample_event_took(u64 sample_len_ns) update_perf_cpu_limits(); - irq_work_queue(&perf_duration_work); + if (!irq_work_queue(&perf_duration_work)) { + early_printk("perf interrupt took too long (%lld > %lld), lowering " + "kernel.perf_event_max_sample_rate to %d\n", + avg_local_sample_len, allowed_ns >> 1, + sysctl_perf_event_sample_rate); + } } static atomic64_t perf_event_id; diff --git a/kernel/irq_work.c b/kernel/irq_work.c index 55fcce6..a82170e 100644 --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -61,11 +61,11 @@ void __weak arch_irq_work_raise(void) * * Can be re-enqueued while the callback is still in progress. */ -void irq_work_queue(struct irq_work *work) +bool irq_work_queue(struct irq_work *work) { /* Only queue if not already pending */ if (!irq_work_claim(work)) - return; + return false; /* Queue the entry and raise the IPI if needed. */ preempt_disable(); @@ -83,6 +83,8 @@ void irq_work_queue(struct irq_work *work) } preempt_enable(); + + return true; } EXPORT_SYMBOL_GPL(irq_work_queue); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/