linux-kernel - [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to 'unsigned int'

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Message-ID: <20160315095337.GC7943@gmail.com>
Date:	Tue, 15 Mar 2016 10:53:37 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to 'unsigned
 int'


Linus noticed that the new tick_dep_mask types introduced in:

  d027d45d8a17 ("nohz: New tick dependency mask")

... are sloppily defined as 'unsigned long' - which is wasteful
to carry just 4 bits and which may also create suboptimal data
types on 64-bit systems with word alignment padding holes in them.

Fix this by changing the type to the more natural 'unsigned int'.

(The xchg_or() API will work fine with 'unsigned int' as well.)

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Chris Metcalf <cmetcalf@...hip.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Chris Metcalf <cmetcalf@...hip.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/sched.h    |  4 ++--
 kernel/time/tick-sched.c | 11 +++++------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c617ea12c6b7..6d1842bb7abd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -718,7 +718,7 @@ struct signal_struct {
 	struct task_cputime cputime_expires;
 
 #ifdef CONFIG_NO_HZ_FULL
-	unsigned long tick_dep_mask;
+	unsigned int tick_dep_mask;
 #endif
 
 	struct list_head cpu_timers[3];
@@ -1548,7 +1548,7 @@ struct task_struct {
 #endif
 
 #ifdef CONFIG_NO_HZ_FULL
-	unsigned long tick_dep_mask;
+	unsigned int tick_dep_mask;
 #endif
 	unsigned long nvcsw, nivcsw; /* context switch counts */
 	u64 start_time;		/* monotonic time in nsec */
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 851631899352..fe0f57f3432f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -157,9 +157,9 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
 cpumask_var_t tick_nohz_full_mask;
 cpumask_var_t housekeeping_mask;
 bool tick_nohz_full_running;
-static unsigned long tick_dep_mask;
+static unsigned int tick_dep_mask;
 
-static void trace_tick_dependency(unsigned long dep)
+static void trace_tick_dependency(unsigned int dep)
 {
 	if (dep & TICK_DEP_MASK_POSIX_TIMER) {
 		trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
@@ -259,10 +259,9 @@ static void tick_nohz_full_kick_all(void)
 	preempt_enable();
 }
 
-static void tick_nohz_dep_set_all(unsigned long *dep,
-				  enum tick_dep_bits bit)
+static void tick_nohz_dep_set_all(unsigned int *dep, enum tick_dep_bits bit)
 {
-	unsigned long prev;
+	unsigned int prev;
 
 	prev = xchg_or(dep, BIT_MASK(bit));
 	if (!prev)
@@ -289,7 +288,7 @@ void tick_nohz_dep_clear(enum tick_dep_bits bit)
  */
 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
 {
-	unsigned long prev;
+	unsigned int prev;
 	struct tick_sched *ts;
 
 	ts = per_cpu_ptr(&tick_cpu_sched, cpu);