linux-kernel - Re: [RFC v3 1/6] Track the active utilisation

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Date:   Tue, 6 Dec 2016 14:47:47 +0100
From:   luca abeni <luca.abeni@...tn.it>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Claudio Scordino <claudio@...dence.eu.com>
Subject: Re: [RFC v3 1/6] Track the active utilisation

Hi Peter,

On Tue, 6 Dec 2016 09:35:01 +0100
Peter Zijlstra <peterz@...radead.org> wrote:
[...]
> > This is because of the definition used when CONFIG_SCHED_DEBUG is
> > not defined (I noticed the issue when testing with random kernel
> > configurations).  
> 
> I'm fine changing the definition, just find something that works. The
> current ((void)(x)) thing was to avoid unused complaints -- although
> I'm not sure there were any.

Below is what I came up with... It fixes the build, and seems to work
fine generating no warnings (I tested with gcc 5.4.0). To write this
patch, I re-used some code from include/asm-generic/bug.h, that has no
copyright header, so I just added my signed-off-by (but I am not sure
if this is the correct way to go).


				Luca



From 74e67d61c4b98c2498880932b953c65e9653c121 Mon Sep 17 00:00:00 2001
From: Luca Abeni <luca.abeni@...tn.it>
Date: Tue, 6 Dec 2016 10:02:28 +0100
Subject: [PATCH 7/7] sched.h: Improve SCHED_WARN_ON() when CONFIG_SCHED_DEBUG is not defined

With the current definition of SCHED_WARN_ON(), something like
	if (SCHED_WARN_ON(condition)) ...
fails with
	error: void value not ignored as it ought to be
	 #define SCHED_WARN_ON(x) ((void)(x))
	                          ^

This patch fixes the issue by using the same code used in WARN_ON()

Signed-off-by: Luca Abeni <luca.abeni@...tn.it>
---
 kernel/sched/sched.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ef4bdaa..2e96aa4 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -19,7 +19,10 @@
 #ifdef CONFIG_SCHED_DEBUG
 #define SCHED_WARN_ON(x)	WARN_ONCE(x, #x)
 #else
-#define SCHED_WARN_ON(x)	((void)(x))
+#define SCHED_WARN_ON(x)	({					\
+	int __ret_warn_on = !!(x);					\
+	unlikely(__ret_warn_on);					\
+})
 #endif
 
 struct rq;
-- 
2.7.4