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: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Dave Hansen <[email protected]>
Cc: [email protected]
Fixes: 6a02ad66b2c4 ("perf/x86: Push the duration-logging printk() to IRQ context")
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index add13c8624b7..19ae05d4b8ec 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);