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Subject[tip:timers/core] hrtimer: Make the remote enqueue check unconditional
Commit-ID:  07a9a7eae86abb796468b225586086d7c4cb59fc
Gitweb: https://git.kernel.org/tip/07a9a7eae86abb796468b225586086d7c4cb59fc
Author: Anna-Maria Gleixner <anna-maria@linutronix.de>
AuthorDate: Thu, 21 Dec 2017 11:41:44 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 16 Jan 2018 02:35:47 +0100

hrtimer: Make the remote enqueue check unconditional

hrtimer_cpu_base.expires_next is used to cache the next event armed in the
timer hardware. The value is used to check whether an hrtimer can be
enqueued remotely. If the new hrtimer is expiring before expires_next, then
remote enqueue is not possible as the remote hrtimer hardware cannot be
accessed for reprogramming to an earlier expiry time.

The remote enqueue check is currently conditional on
CONFIG_HIGH_RES_TIMERS=y and hrtimer_cpu_base.hres_active. There is no
compelling reason to make this conditional.

Move hrtimer_cpu_base.expires_next out of the CONFIG_HIGH_RES_TIMERS=y
guarded area and remove the conditionals in hrtimer_check_target().

The check is currently a NOOP for the CONFIG_HIGH_RES_TIMERS=n and the
!hrtimer_cpu_base.hres_active case because in these cases nothing updates
hrtimer_cpu_base.expires_next yet. This will be changed with later patches
which further reduce the #ifdef zoo in this code.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: keescook@chromium.org
Link: http://lkml.kernel.org/r/20171221104205.7269-16-anna-maria@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/hrtimer.h | 6 +++---
kernel/time/hrtimer.c | 26 ++++++--------------------
2 files changed, 9 insertions(+), 23 deletions(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 22627b3..bb7270e 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -164,13 +164,13 @@ enum hrtimer_base_type {
* @hres_active: State of high resolution mode
* @in_hrtirq: hrtimer_interrupt() is currently executing
* @hang_detected: The last hrtimer interrupt detected a hang
- * @expires_next: absolute time of the next event, is required for remote
- * hrtimer enqueue
* @next_timer: Pointer to the first expiring timer
* @nr_events: Total number of hrtimer interrupt events
* @nr_retries: Total number of hrtimer interrupt retries
* @nr_hangs: Total number of hrtimer interrupt hangs
* @max_hang_time: Maximum time spent in hrtimer_interrupt
+ * @expires_next: absolute time of the next event, is required for remote
+ * hrtimer enqueue
* @clock_base: array of clock bases for this cpu
*
* Note: next_timer is just an optimization for __remove_hrtimer().
@@ -186,13 +186,13 @@ struct hrtimer_cpu_base {
#ifdef CONFIG_HIGH_RES_TIMERS
unsigned int in_hrtirq : 1,
hang_detected : 1;
- ktime_t expires_next;
struct hrtimer *next_timer;
unsigned int nr_events;
unsigned short nr_retries;
unsigned short nr_hangs;
unsigned int max_hang_time;
#endif
+ ktime_t expires_next;
struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
} ____cacheline_aligned;

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 5a624f9..a9ab67f 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -154,26 +154,21 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
}

/*
- * With HIGHRES=y we do not migrate the timer when it is expiring
- * before the next event on the target cpu because we cannot reprogram
- * the target cpu hardware and we would cause it to fire late.
+ * We do not migrate the timer when it is expiring before the next
+ * event on the target cpu. When high resolution is enabled, we cannot
+ * reprogram the target cpu hardware and we would cause it to fire
+ * late. To keep it simple, we handle the high resolution enabled and
+ * disabled case similar.
*
* Called with cpu_base->lock of target cpu held.
*/
static int
hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
{
-#ifdef CONFIG_HIGH_RES_TIMERS
ktime_t expires;

- if (!new_base->cpu_base->hres_active)
- return 0;
-
expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);
return expires <= new_base->cpu_base->expires_next;
-#else
- return 0;
-#endif
}

static inline
@@ -657,14 +652,6 @@ static void hrtimer_reprogram(struct hrtimer *timer,
}

/*
- * Initialize the high resolution related parts of cpu_base
- */
-static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base)
-{
- base->expires_next = KTIME_MAX;
-}
-
-/*
* Retrigger next event is called after clock was set
*
* Called with interrupts disabled via on_each_cpu()
@@ -729,7 +716,6 @@ static inline int hrtimer_reprogram(struct hrtimer *timer,
{
return 0;
}
-static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }
static inline void retrigger_next_event(void *arg) { }

#endif /* CONFIG_HIGH_RES_TIMERS */
@@ -1599,7 +1585,7 @@ int hrtimers_prepare_cpu(unsigned int cpu)

cpu_base->cpu = cpu;
cpu_base->hres_active = 0;
- hrtimer_init_hres(cpu_base);
+ cpu_base->expires_next = KTIME_MAX;
return 0;
}

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