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Date: Thu, 24 Mar 2016 15:38:00 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 2/3] nohz: Convert tick dependency mask to atomic_t
The tick dependency mask was intially unsigned long because this is the
type on which clear_bit() operates on and fetch_or() accepts it.
But now that we have atomic_fetch_or(), we can instead use
atomic_andnot() to clear the bit. This consolidates the type of our
tick dependency mask, reduce its size on structures and benefit from
possible architecture optimizations on atomic_t operations.
Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
include/linux/sched.h | 4 ++--
kernel/time/tick-sched.c | 61 ++++++++++++++++++++++++------------------------
kernel/time/tick-sched.h | 2 +-
3 files changed, 33 insertions(+), 34 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 34495d2..a43a593 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -719,7 +719,7 @@ struct signal_struct {
struct task_cputime cputime_expires;
#ifdef CONFIG_NO_HZ_FULL
- unsigned long tick_dep_mask;
+ atomic_t 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;
+ atomic_t 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 084b79f..58e3310 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -157,52 +157,50 @@ 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 atomic_t tick_dep_mask;
-static void trace_tick_dependency(unsigned long dep)
+static bool check_tick_dependency(atomic_t *dep)
{
- if (dep & TICK_DEP_MASK_POSIX_TIMER) {
+ int val = atomic_read(dep);
+
+ if (val & TICK_DEP_MASK_POSIX_TIMER) {
trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
- return;
+ return true;
}
- if (dep & TICK_DEP_MASK_PERF_EVENTS) {
+ if (val & TICK_DEP_MASK_PERF_EVENTS) {
trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
- return;
+ return true;
}
- if (dep & TICK_DEP_MASK_SCHED) {
+ if (val & TICK_DEP_MASK_SCHED) {
trace_tick_stop(0, TICK_DEP_MASK_SCHED);
- return;
+ return true;
}
- if (dep & TICK_DEP_MASK_CLOCK_UNSTABLE)
+ if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
+ return true;
+ }
+
+ return false;
}
static bool can_stop_full_tick(struct tick_sched *ts)
{
WARN_ON_ONCE(!irqs_disabled());
- if (tick_dep_mask) {
- trace_tick_dependency(tick_dep_mask);
+ if (check_tick_dependency(&tick_dep_mask))
return false;
- }
- if (ts->tick_dep_mask) {
- trace_tick_dependency(ts->tick_dep_mask);
+ if (check_tick_dependency(&ts->tick_dep_mask))
return false;
- }
- if (current->tick_dep_mask) {
- trace_tick_dependency(current->tick_dep_mask);
+ if (check_tick_dependency(¤t->tick_dep_mask))
return false;
- }
- if (current->signal->tick_dep_mask) {
- trace_tick_dependency(current->signal->tick_dep_mask);
+ if (check_tick_dependency(¤t->signal->tick_dep_mask))
return false;
- }
return true;
}
@@ -259,12 +257,12 @@ static void tick_nohz_full_kick_all(void)
preempt_enable();
}
-static void tick_nohz_dep_set_all(unsigned long *dep,
+static void tick_nohz_dep_set_all(atomic_t *dep,
enum tick_dep_bits bit)
{
- unsigned long prev;
+ int prev;
- prev = fetch_or(dep, BIT_MASK(bit));
+ prev = atomic_fetch_or(dep, BIT(bit));
if (!prev)
tick_nohz_full_kick_all();
}
@@ -280,7 +278,7 @@ void tick_nohz_dep_set(enum tick_dep_bits bit)
void tick_nohz_dep_clear(enum tick_dep_bits bit)
{
- clear_bit(bit, &tick_dep_mask);
+ atomic_andnot(BIT(bit), &tick_dep_mask);
}
/*
@@ -289,12 +287,12 @@ 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;
+ int prev;
struct tick_sched *ts;
ts = per_cpu_ptr(&tick_cpu_sched, cpu);
- prev = fetch_or(&ts->tick_dep_mask, BIT_MASK(bit));
+ prev = atomic_fetch_or(&ts->tick_dep_mask, BIT(bit));
if (!prev) {
preempt_disable();
/* Perf needs local kick that is NMI safe */
@@ -313,7 +311,7 @@ void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
{
struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
- clear_bit(bit, &ts->tick_dep_mask);
+ atomic_andnot(BIT(bit), &ts->tick_dep_mask);
}
/*
@@ -331,7 +329,7 @@ void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
{
- clear_bit(bit, &tsk->tick_dep_mask);
+ atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
}
/*
@@ -345,7 +343,7 @@ void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
{
- clear_bit(bit, &sig->tick_dep_mask);
+ atomic_andnot(BIT(bit), &sig->tick_dep_mask);
}
/*
@@ -366,7 +364,8 @@ void __tick_nohz_task_switch(void)
ts = this_cpu_ptr(&tick_cpu_sched);
if (ts->tick_stopped) {
- if (current->tick_dep_mask || current->signal->tick_dep_mask)
+ if (atomic_read(¤t->tick_dep_mask) ||
+ atomic_read(¤t->signal->tick_dep_mask))
tick_nohz_full_kick();
}
out:
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index eb4e325..bf38226 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -60,7 +60,7 @@ struct tick_sched {
u64 next_timer;
ktime_t idle_expires;
int do_timer_last;
- unsigned long tick_dep_mask;
+ atomic_t tick_dep_mask;
};
extern struct tick_sched *tick_get_tick_sched(int cpu);
--
2.7.0
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