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Date: Mon, 29 Jul 2013 13:57:01 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: "ethan.zhao" <ethan.kernel@...il.com>,
Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>, johlstei@...eaurora.org,
yinghai@...nel.org, joe.jin@...cle.com
Subject: Re: [PATCH V3]hrtimer: Fix a performance regression by disable
reprogramming in remove_hrtimer
On Mon, Jul 29, 2013 at 12:18:11PM +0200, Thomas Gleixner wrote:
> The reason why we want to do that is:
>
> timer expiry time
> A 100us -> programmed hardware event
> B 2000us
>
> Restart timer A with an expiry time of 3000us without reprogramming:
>
> timer expiry time
> NONE 100us -> programmed hardware event
> B 2000us
> A 3000us
>
> We take an extra wakeup for reprogramming the hardware, which is
> counterproductive for power saving. So disabling it blindly will cause
> a regresssion for other people. We need to be smarter than that.
So aside from the complete mess posted; how about something like this?
*completely untested etc..*
---
include/linux/hrtimer.h | 5 +++++
kernel/hrtimer.c | 60 +++++++++++++++++++++++--------------------------
2 files changed, 33 insertions(+), 32 deletions(-)
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index d19a5c2..f2bcb9c 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -185,6 +185,7 @@ struct hrtimer_cpu_base {
ktime_t expires_next;
int hres_active;
int hang_detected;
+ int timers_removed;
unsigned long nr_events;
unsigned long nr_retries;
unsigned long nr_hangs;
@@ -261,6 +262,8 @@ static inline ktime_t hrtimer_expires_remaining(const struct hrtimer *timer)
#ifdef CONFIG_HIGH_RES_TIMERS
struct clock_event_device;
+extern void hrtimer_enter_idle(void);
+
extern void hrtimer_interrupt(struct clock_event_device *dev);
/*
@@ -296,6 +299,8 @@ extern void clock_was_set_delayed(void);
# define MONOTONIC_RES_NSEC LOW_RES_NSEC
# define KTIME_MONOTONIC_RES KTIME_LOW_RES
+static inline void hrtimer_enter_idle(void) { }
+
static inline void hrtimer_peek_ahead_timers(void) { }
/*
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index f0f4fe2..ffb16d3 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -673,6 +673,27 @@ static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base)
return ktime_get_update_offsets(offs_real, offs_boot, offs_tai);
}
+static void __hrtimer_reprogram_all(struct hrtimer_cpu_base *base)
+{
+ if (!hrtimer_hres_active())
+ return;
+
+ raw_spin_lock(&base->lock);
+ hrtimer_update_base(base);
+ hrtimer_force_reprogram(base, 0);
+ raw_spin_unlock(&base->lock);
+}
+
+void hrtimer_enter_idle(void)
+{
+ struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);
+
+ if (base->timers_removed) {
+ base->timers_removed = 0;
+ __hrtimer_reprogramm_all(base);
+ }
+}
+
/*
* Retrigger next event is called after clock was set
*
@@ -682,13 +703,7 @@ static void retrigger_next_event(void *arg)
{
struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);
- if (!hrtimer_hres_active())
- return;
-
- raw_spin_lock(&base->lock);
- hrtimer_update_base(base);
- hrtimer_force_reprogram(base, 0);
- raw_spin_unlock(&base->lock);
+ __hrtimer_reprogram_all(base);
}
/*
@@ -907,7 +922,7 @@ static int enqueue_hrtimer(struct hrtimer *timer,
*/
static void __remove_hrtimer(struct hrtimer *timer,
struct hrtimer_clock_base *base,
- unsigned long newstate, int reprogram)
+ unsigned long newstate)
{
struct timerqueue_node *next_timer;
if (!(timer->state & HRTIMER_STATE_ENQUEUED))
@@ -915,19 +930,10 @@ static void __remove_hrtimer(struct hrtimer *timer,
next_timer = timerqueue_getnext(&base->active);
timerqueue_del(&base->active, &timer->node);
- if (&timer->node == next_timer) {
#ifdef CONFIG_HIGH_RES_TIMERS
- /* Reprogram the clock event device. if enabled */
- if (reprogram && hrtimer_hres_active()) {
- ktime_t expires;
-
- expires = ktime_sub(hrtimer_get_expires(timer),
- base->offset);
- if (base->cpu_base->expires_next.tv64 == expires.tv64)
- hrtimer_force_reprogram(base->cpu_base, 1);
- }
+ if (hrtimer_hres_active() && &timer->node == next_timer)
+ base->cpu_base->timers_removed++;
#endif
- }
if (!timerqueue_getnext(&base->active))
base->cpu_base->active_bases &= ~(1 << base->index);
out:
@@ -942,26 +948,16 @@ remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base)
{
if (hrtimer_is_queued(timer)) {
unsigned long state;
- int reprogram;
- /*
- * Remove the timer and force reprogramming when high
- * resolution mode is active and the timer is on the current
- * CPU. If we remove a timer on another CPU, reprogramming is
- * skipped. The interrupt event on this CPU is fired and
- * reprogramming happens in the interrupt handler. This is a
- * rare case and less expensive than a smp call.
- */
debug_deactivate(timer);
timer_stats_hrtimer_clear_start_info(timer);
- reprogram = base->cpu_base == &__get_cpu_var(hrtimer_bases);
/*
* We must preserve the CALLBACK state flag here,
* otherwise we could move the timer base in
* switch_hrtimer_base.
*/
state = timer->state & HRTIMER_STATE_CALLBACK;
- __remove_hrtimer(timer, base, state, reprogram);
+ __remove_hrtimer(timer, base, state);
return 1;
}
return 0;
@@ -1243,7 +1239,7 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
WARN_ON(!irqs_disabled());
debug_deactivate(timer);
- __remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK, 0);
+ __remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK);
timer_stats_account_hrtimer(timer);
fn = timer->function;
@@ -1690,7 +1686,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
* timer could be seen as !active and just vanish away
* under us on another CPU
*/
- __remove_hrtimer(timer, old_base, HRTIMER_STATE_MIGRATE, 0);
+ __remove_hrtimer(timer, old_base, HRTIMER_STATE_MIGRATE);
timer->base = new_base;
/*
* Enqueue the timers on the new cpu. This does not
--
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