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Subject[patch 09/12] hrtimer: Move unmarked hrtimers to soft interrupt expiry on RT
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

On PREEMPT_RT not all hrtimers can be expired in hard interrupt context
even if that is perfectly fine on a PREEMPT_RT=n kernel, e.g. because they
take regular spinlocks. Also for latency reasons PREEMPT_RT tries to defer
most hrtimers' expiry into softirq context.

hrtimers marked with HRTIMER_MODE_HARD must be kept in hard interrupt
context expiry mode. Add the required logic.

No functional change for PREEMPT_RT=n kernels.

[ tglx: Split out of a larger combo patch. Added changelog ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/hrtimer.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1271,8 +1271,16 @@ static void __hrtimer_init(struct hrtime
enum hrtimer_mode mode)
{
bool softtimer = !!(mode & HRTIMER_MODE_SOFT);
- int base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;
struct hrtimer_cpu_base *cpu_base;
+ int base;
+
+ /*
+ * On PREEMPT_RT enabled kernels hrtimers which are not explicitely
+ * marked for hard interrupt expiry mode are moved into soft
+ * interrupt context for latency reasons.
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(mode & HRTIMER_MODE_HARD))
+ softtimer = true;

memset(timer, 0, sizeof(struct hrtimer));

@@ -1286,6 +1294,7 @@ static void __hrtimer_init(struct hrtime
if (clock_id == CLOCK_REALTIME && mode & HRTIMER_MODE_REL)
clock_id = CLOCK_MONOTONIC;

+ base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;
base += hrtimer_clockid_to_base(clock_id);
timer->is_soft = softtimer;
timer->base = &cpu_base->clock_base[base];

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