Re: [PATCH v3 4/4] nmi_backtrace: generate one-line reports for idle cpus

From: Peter Zijlstra
Date: Tue Mar 22 2016 - 13:30:18 EST

On Tue, Mar 22, 2016 at 01:19:39PM -0400, Chris Metcalf wrote:
> When doing an nmi backtrace of many cores, most of which are idle,
> the output is a little overwhelming and very uninformative. Suppress
> messages for cpus that are idling when they are interrupted and just
> emit one line, "NMI backtrace for N skipped: idling at pc 0xNNN".
> We do this by grouping all the cpuidle code together into a new
> .cpuidle.text section, and then checking the address of the
> interrupted PC to see if it lies within that section.
> This commit suitably tags x86, arm64, and tile idle routines,
> and only adds in the minimal framework for other architectures.
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Tested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>

For some reason I found a few CPUs using poll_idle().

Rafael, when and why would that ever get selected as a useful idle
state? When the predicted idle time is so short even C1 isn't worth it?

--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c
@@ -14,6 +14,7 @@
#include <linux/cpuidle.h>
#include <linux/cpumask.h>
#include <linux/tick.h>
+#include <linux/cpu.h>

#include "cpuidle.h"

@@ -178,7 +179,7 @@ static void __cpuidle_driver_init(struct

-static int poll_idle(struct cpuidle_device *dev,
+__cpuidle static int poll_idle(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)