Commit-ID: 61bb4bcb79c7afcd0bf0d20aef4704977172fd60
Gitweb: https://git.kernel.org/tip/61bb4bcb79c7afcd0bf0d20aef4704977172fd60
Author: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
AuthorDate: Thu, 21 Dec 2017 11:41:48 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 16 Jan 2018 02:53:58 +0100
hrtimer: Unify hrtimer removal handling
When the first hrtimer on the current CPU is removed,
hrtimer_force_reprogram() is invoked but only when
CONFIG_HIGH_RES_TIMERS=y and hrtimer_cpu_base.hres_active is set.
hrtimer_force_reprogram() updates hrtimer_cpu_base.expires_next and
reprograms the clock event device. When CONFIG_HIGH_RES_TIMERS=y and
hrtimer_cpu_base.hres_active is set, a pointless hrtimer interrupt can be
prevented.
hrtimer_check_target() makes the 'can remote enqueue' decision. As soon as
hrtimer_check_target() is unconditionally available and
hrtimer_cpu_base.expires_next is updated by hrtimer_reprogram(),
hrtimer_force_reprogram() needs to be available unconditionally as well to
prevent the following scenario with CONFIG_HIGH_RES_TIMERS=n:
- the first hrtimer on this CPU is removed and hrtimer_force_reprogram() is
not executed
- CPU goes idle (next timer is calculated and hrtimers are taken into
account)
- a hrtimer is enqueued remote on the idle CPU: hrtimer_check_target()
compares expiry value and hrtimer_cpu_base.expires_next. The expiry value
is after expires_next, so the hrtimer is enqueued. This timer will fire
late, if it expires before the effective first hrtimer on this CPU and
the comparison was with an outdated expires_next value.
To prevent this scenario, make hrtimer_force_reprogram() unconditional
except the effective reprogramming part, which gets eliminated by the
compiler in the CONFIG_HIGH_RES_TIMERS=n case.
Signed-off-by: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: keescook@xxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20171221104205.7269-20-anna-maria@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/time/hrtimer.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 2b3222e..e6a78ae 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -521,9 +521,6 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
{
ktime_t expires_next;
- if (!__hrtimer_hres_active(cpu_base))
- return;
-
expires_next = __hrtimer_get_next_event(cpu_base);
if (skip_equal && expires_next == cpu_base->expires_next)
@@ -532,6 +529,9 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
cpu_base->expires_next = expires_next;
/*
+ * If hres is not active, hardware does not have to be
+ * reprogrammed yet.
+ *
* If a hang was detected in the last timer interrupt then we
* leave the hang delay active in the hardware. We want the
* system to make progress. That also prevents the following
@@ -545,7 +545,7 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
* set. So we'd effectivly block all timers until the T2 event
* fires.
*/
- if (cpu_base->hang_detected)
+ if (!__hrtimer_hres_active(cpu_base) || cpu_base->hang_detected)
return;
tick_program_event(cpu_base->expires_next, 1);
@@ -844,7 +844,6 @@ static void __remove_hrtimer(struct hrtimer *timer,
if (!timerqueue_del(&base->active, &timer->node))
cpu_base->active_bases &= ~(1 << base->index);
-#ifdef CONFIG_HIGH_RES_TIMERS
/*
* Note: If reprogram is false we do not update
* cpu_base->next_timer. This happens when we remove the first
@@ -855,7 +854,6 @@ static void __remove_hrtimer(struct hrtimer *timer,
*/
if (reprogram && timer == cpu_base->next_timer)
hrtimer_force_reprogram(cpu_base, 1);
-#endif
}
/*
--
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