On Mon, Mar 27, 2017 at 05:15:00PM +0200, Jesper Dangaard Brouer wrote:
> And I also verified it worked:
>
> 0.63 │ mov __preempt_count,%eax
> │ free_hot_cold_page():
> 1.25 │ test $0x1f0000,%eax
> │ ↓ jne 1e4
>
> And this simplification also made the compiler change this into a
> unlikely branch, which is a micro-optimization (that I will leave up to
> the compiler).
Excellent! That said, I think we should define in_irq_or_nmi() in
preempt.h, rather than hiding it in the memory allocator. And since we're
doing that, we might as well make it look like the other definitions:
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 7eeceac52dea..af98c29abd9d 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -81,6 +81,7 @@
#define in_interrupt() (irq_count())
#define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET)
#define in_nmi() (preempt_count() & NMI_MASK)
+#define in_irq_or_nmi() (preempt_count() & (HARDIRQ_MASK |
NMI_MASK))
#define in_task() (!(preempt_count() & \
(NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
I think there are some genuine questions to be asked about the other
users of in_irq() whether they really want to use in_irq_or_nmi().
There's fewer than a hundred of them, so somebody sufficiently motivated
could take a look in a few days.
