linux-kernel - [PATCH 4/4] sched/deadline: use C bitfields for the state flags

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Date:   Thu,  7 Sep 2017 12:09:31 +0200
From:   luca abeni <luca.abeni@...tannapisa.it>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        luca abeni <luca.abeni@...tannapisa.it>
Subject: [PATCH 4/4] sched/deadline: use C bitfields for the state flags

Ask the compiler to use a single bit for storing true / false values,
instead of wasting the size of a whole int value.
Tested with gcc 5.4.0 on x86_64, and the compiler produces the expected
Assembly (similar to the Assembly code generated when explicitly accessing
the bits with bitmasks, "&" and "|").

Signed-off-by: luca abeni <luca.abeni@...tannapisa.it>
---
 include/linux/sched.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 68b3833..e03cc69 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -472,10 +472,10 @@ struct sched_dl_entity {
 	 * conditions between the inactive timer handler and the wakeup
 	 * code.
 	 */
-	int				dl_throttled;
-	int				dl_boosted;
-	int				dl_yielded;
-	int				dl_non_contending;
+	int				dl_throttled      : 1;
+	int				dl_boosted        : 1;
+	int				dl_yielded        : 1;
+	int				dl_non_contending : 1;
 
 	/*
 	 * Bandwidth enforcement timer. Each -deadline task has its
-- 
2.7.4