lkml.org 
[lkml]   [2019]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:timers/core] hrtimer: Move unmarked hrtimers to soft interrupt expiry on RT
Commit-ID:  edd2f987491fb47949a9612743435d6d0f61f614
Gitweb: https://git.kernel.org/tip/edd2f987491fb47949a9612743435d6d0f61f614
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Fri, 26 Jul 2019 20:30:57 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 1 Aug 2019 17:43:19 +0200

hrtimer: Move unmarked hrtimers to soft interrupt expiry on RT

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>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190726185753.551967692@linutronix.de


---
kernel/time/hrtimer.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 0ace301a56f4..90dcc4d95e91 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1275,8 +1275,17 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
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 and because the callbacks
+ * can invoke functions which might sleep on RT, e.g. spin_lock().
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(mode & HRTIMER_MODE_HARD))
+ softtimer = true;

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

@@ -1290,6 +1299,7 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
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->is_hard = !softtimer;
\
 
 \ /
  Last update: 2019-08-01 18:27    [W:0.300 / U:7.936 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site