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

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Message-ID: <20160322173005.GT6344@twins.programming.kicks-ass.net>
Date:	Tue, 22 Mar 2016 18:30:05 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Metcalf <cmetcalf@...lanox.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Andrew Morton <akpm@...l.org>,
	Daniel Thompson <daniel.thompson@...aro.org>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH v3 4/4] nmi_backtrace: generate one-line reports for idle
 cpus

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@...radead.org>
> Tested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Chris Metcalf <cmetcalf@...lanox.com>

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
 }
 
 #ifdef CONFIG_ARCH_HAS_CPU_RELAX
-static int poll_idle(struct cpuidle_device *dev,
+__cpuidle static int poll_idle(struct cpuidle_device *dev,
 		struct cpuidle_driver *drv, int index)
 {
 	local_irq_enable();