From: Haris Okanovic <haris.okanovic@ni.com>
To: <linux-rt-users@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Cc: <haris.okanovic@ni.com>, <harisokn@gmail.com>,
<bigeasy@linutronix.de>, <tglx@linutronix.de>,
<julia.cartwright@ni.com>, <gratian.crisan@ni.com>,
<anna-maria@linutronix.de>, <daniel@bristot.me>
Subject: [PATCH v4 2/2] timers: Don't search for expired timers while TIMER_SOFTIRQ is scheduled
Date: Tue, 6 Mar 2018 17:39:44 -0600 [thread overview]
Message-ID: <20180306233944.11271-2-haris.okanovic@ni.com> (raw)
In-Reply-To: <20180306233944.11271-1-haris.okanovic@ni.com>
This change avoid needlessly searching for more timers in
run_local_timers() (hard interrupt context) when they can't fire.
For example, when ktimersoftd/run_timer_softirq() is scheduled but
preempted due to cpu contention. When it runs, run_timer_softirq() will
discover newly expired timers up to current jiffies in addition to
firing previously expired timers.
However, this change also adds an edge case where non-hrtimer firing
is sometimes delayed by an additional tick. This is acceptable since we
don't make latency guarantees for non-hrtimers and would prefer to
minimize hard interrupt time instead.
Signed-off-by: Haris Okanovic <haris.okanovic@ni.com>
---
[PATCH v3]
- Split block_softirq into separate commit
[PATCH v4]
- Rebase onto v4.14.20-rt17
https://github.com/harisokanovic/linux/tree/dev/hokanovi/timer-peek-v6
---
kernel/time/timer.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 98e952a6428d..5687e9bcf378 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -207,6 +207,7 @@ struct timer_base {
unsigned int cpu;
bool is_idle;
bool must_forward_clk;
+ bool block_softirq;
DECLARE_BITMAP(pending_map, WHEEL_SIZE);
struct hlist_head vectors[WHEEL_SIZE];
struct hlist_head expired_lists[LVL_DEPTH];
@@ -1404,9 +1405,11 @@ static int __collect_expired_timers(struct timer_base *base)
/*
* expire_timers() must be called at least once before we can
- * collect more timers.
+ * collect more timers. We should never hit this case unless
+ * TIMER_SOFTIRQ got raised without expired timers.
*/
- if (base->expired_levels)
+ if (WARN_ONCE(base->expired_levels,
+ "Must expire collected timers before collecting more"))
return base->expired_levels;
clk = base->clk;
@@ -1748,6 +1751,9 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h)
__run_timers(base);
if (IS_ENABLED(CONFIG_NO_HZ_COMMON))
__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
+
+ /* Allow new TIMER_SOFTIRQs to get scheduled by run_local_timers() */
+ base->block_softirq = false;
}
/*
@@ -1758,6 +1764,14 @@ void run_local_timers(void)
struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
hrtimer_run_queues();
+
+ /*
+ * Skip if TIMER_SOFTIRQ is already running on this CPU, since it
+ * will find and expire all timers up to current jiffies.
+ */
+ if (base->block_softirq)
+ return;
+
/* Raise the softirq only if required. */
if (time_before(jiffies, base->clk) || !tick_find_expired(base)) {
if (!IS_ENABLED(CONFIG_NO_HZ_COMMON))
@@ -1766,7 +1780,10 @@ void run_local_timers(void)
base++;
if (time_before(jiffies, base->clk) || !tick_find_expired(base))
return;
+ base--;
}
+
+ base->block_softirq = true;
raise_softirq(TIMER_SOFTIRQ);
}
--
2.15.1
next prev parent reply other threads:[~2018-03-06 23:40 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-13 21:44 [RFC v2] timers: Don't wake ktimersoftd on every tick Haris Okanovic
2016-12-23 17:28 ` Sebastian Andrzej Siewior
2016-12-28 18:06 ` Haris Okanovic
2017-02-03 16:51 ` Sebastian Andrzej Siewior
2017-02-03 18:21 ` [PATCH] " Haris Okanovic
2017-02-10 17:02 ` Sebastian Andrzej Siewior
2017-05-26 17:16 ` [PATCH] Revert "timers: Don't wake ktimersoftd on every tick" Anna-Maria Gleixner
2017-05-26 19:27 ` Haris Okanovic
2017-05-26 19:49 ` Thomas Gleixner
2017-05-26 20:25 ` Haris Okanovic
2017-05-26 20:50 ` Thomas Gleixner
2017-06-02 14:37 ` Haris Okanovic
2017-06-04 14:17 ` Thomas Gleixner
2017-07-17 21:58 ` Haris Okanovic
2017-07-17 22:04 ` [PATCH v2] timers: Don't wake ktimersoftd on every tick Haris Okanovic
2017-07-18 21:33 ` Thomas Gleixner
2017-08-03 21:04 ` Haris Okanovic
2017-08-03 21:06 ` [PATCH v3 1/2] " Haris Okanovic
2017-08-03 21:06 ` [PATCH v3 2/2] timers: Don't search for expired timers while TIMER_SOFTIRQ is scheduled Haris Okanovic
2018-01-05 19:37 ` Haris Okanovic
2018-03-01 15:49 ` Haris Okanovic
2018-03-01 15:54 ` Thomas Gleixner
2018-03-01 16:35 ` Haris Okanovic
2018-03-01 16:47 ` Sebastian Andrzej Siewior
2018-03-01 18:37 ` Haris Okanovic
2018-03-01 19:06 ` Sebastian Andrzej Siewior
2018-03-02 14:52 ` Sebastian Andrzej Siewior
2018-03-02 16:29 ` Haris Okanovic
2018-03-02 16:39 ` Sebastian Andrzej Siewior
2018-03-02 17:19 ` Haris Okanovic
2018-03-06 23:39 ` [PATCH v4 1/2] timers: Don't wake ktimersoftd on every tick Haris Okanovic
2018-03-06 23:39 ` Haris Okanovic [this message]
[not found] ` <1523332961.4827.1.camel@gmx.de>
2018-04-12 15:00 ` Haris Okanovic
2018-06-19 12:43 ` Daniel Bristot de Oliveira
2018-06-20 14:24 ` Haris Okanovic
2018-06-28 16:36 ` Haris Okanovic
2018-06-28 16:40 ` [PATCH v5 " Haris Okanovic
2018-06-28 16:40 ` [PATCH v5 2/2] timers: Don't search for expired timers while TIMER_SOFTIRQ is scheduled Haris Okanovic
2018-07-13 12:01 ` [PATCH v5 1/2] timers: Don't wake ktimersoftd on every tick Anna-Maria Gleixner
2018-07-13 14:37 ` Haris Okanovic
2017-05-27 7:47 ` [PATCH] Revert "timers: Don't wake ktimersoftd on every tick" Sebastian Andrzej Siewior
2017-02-03 18:27 ` [RFC v2] timers: Don't wake ktimersoftd on every tick Haris Okanovic
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