Commit cd578abb authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

perf/x86: Warn to early_printk() in case irq_work is too slow 



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.

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.

Cc: hpa@zytor.com
Cc: tglx@linutronix.de
Cc: dzickus@redhat.com
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: mingo@kernel.org
Fixes: 6a02ad66 ("perf/x86: Push the duration-logging printk() to IRQ context")
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140211150116.GO27965@twins.programming.kicks-ass.net


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 90ed5b0f

include/linux/irq_work.h

+1 −1
Original line number Diff line number Diff line
@@ -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);

kernel/events/core.c

+7 −2
Original line number Diff line number Diff line
@@ -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;

kernel/irq_work.c

+4 −2
Original line number Diff line number Diff line
@@ -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);

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