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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org,
	linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	John Kacur <jkacur@redhat.com>,
	Paul Gortmaker <paul.gortmaker@windriver.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Mike Galbraith <bitbucket@online.de>
Subject: [PATCH RT 35/39] timers: Reduce __run_timers() latency for empty list
Date: Thu, 12 Mar 2015 15:13:42 -0400	[thread overview]
Message-ID: <20150312191412.783756948@goodmis.org> (raw)
In-Reply-To: 20150312191307.081068717@goodmis.org

[-- Attachment #1: 0035-timers-Reduce-__run_timers-latency-for-empty-list.patch --]
[-- Type: text/plain, Size: 2130 bytes --]

3.14.34-rt32-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

upstream commit: d550e81dc0ddc04f1b417c179c214103a28e0ee8

The __run_timers() function currently steps through the list one jiffy at
a time in order to update the timer wheel.  However, if the timer wheel
is empty, no adjustment is needed other than updating ->timer_jiffies.
In this case, which is likely to be common for NO_HZ_FULL kernels, the
kernel currently incurs a large latency for no good reason.  This commit
therefore short-circuits this case.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Mike Galbraith <bitbucket@online.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/timer.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/kernel/timer.c b/kernel/timer.c
index 251fdacfebdb..9cf70c562fac 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -341,6 +341,20 @@ void set_timer_slack(struct timer_list *timer, int slack_hz)
 }
 EXPORT_SYMBOL_GPL(set_timer_slack);
 
+/*
+ * If the list is empty, catch up ->timer_jiffies to the current time.
+ * The caller must hold the tvec_base lock.  Returns true if the list
+ * was empty and therefore ->timer_jiffies was updated.
+ */
+static bool catchup_timer_jiffies(struct tvec_base *base)
+{
+	if (!base->all_timers) {
+		base->timer_jiffies = jiffies;
+		return true;
+	}
+	return false;
+}
+
 static void
 __internal_add_timer(struct tvec_base *base, struct timer_list *timer)
 {
@@ -1203,6 +1217,10 @@ static inline void __run_timers(struct tvec_base *base)
 	struct timer_list *timer;
 
 	spin_lock_irq(&base->lock);
+	if (catchup_timer_jiffies(base)) {
+		spin_unlock_irq(&base->lock);
+		return;
+	}
 	while (time_after_eq(jiffies, base->timer_jiffies)) {
 		struct list_head work_list;
 		struct list_head *head = &work_list;
-- 
2.1.4



  parent reply	other threads:[~2015-03-12 19:18 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-12 19:13 [PATCH RT 00/39] Linux 3.14.34-rt32-rc1 Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 01/39] gpio: omap: use raw locks for locking Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 02/39] rtmutex: Simplify rtmutex_slowtrylock() Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 03/39] rtmutex: Simplify and document try_to_take_rtmutex() Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 04/39] rtmutex: No need to keep task ref for lock owner check Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 05/39] rtmutex: Clarify the boost/deboost part Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 06/39] rtmutex: Document pi chain walk Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 07/39] rtmutex: Simplify remove_waiter() Steven Rostedt
2015-03-12 19:13   ` Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 08/39] rtmutex: Confine deadlock logic to futex Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 09/39] rtmutex: Cleanup deadlock detector debug logic Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 10/39] rtmutex: Avoid pointless requeueing in the deadlock detection chain walk Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 11/39] futex: Make unlock_pi more robust Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 12/39] futex: Use futex_top_waiter() in lookup_pi_state() Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 13/39] futex: Split out the waiter check from lookup_pi_state() Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 14/39] futex: Split out the first waiter attachment " Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 15/39] futex: Simplify futex_lock_pi_atomic() and make it more robust Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 16/39] locking/rt-mutex: avoid a NULL pointer dereference on deadlock Steven Rostedt
2015-03-13 10:40   ` Sebastian Andrzej Siewior
2015-03-13 10:56     ` Sebastian Andrzej Siewior
2015-03-12 19:13 ` [PATCH RT 17/39] rtmutex.c: Fix incorrect waiter check Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 18/39] rt,locking: fix __ww_mutex_lock_interruptible() lockdep annotation Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 19/39] rtmutex: enable deadlock detection in ww_mutex_lock functions Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 20/39] x86: UV: raw_spinlock conversion Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 22/39] arm/futex: disable preemption during futex_atomic_cmpxchg_inatomic() Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 23/39] ARM: cmpxchg: define __HAVE_ARCH_CMPXCHG for armv6 and later Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 24/39] mips: rt: Replace pagefault_* to raw version Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 25/39] sas-ata/isci: dontt disable interrupts in qc_issue handler Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 26/39] scheduling while atomic in cgroup code Steven Rostedt
2015-03-17 20:10   ` Paul Gortmaker
2015-03-17 20:13     ` Steven Rostedt
2015-03-18  8:37     ` Sebastian Andrzej Siewior
2015-03-18 13:20       ` Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 27/39] work-simple: Simple work queue implemenation Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 28/39] sunrpc: make svc_xprt_do_enqueue() use get_cpu_light() Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 29/39] Revert "rwsem-rt: Do not allow readers to nest" Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 30/39] locking: ww_mutex: fix ww_mutex vs self-deadlock Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 31/39] thermal: Defer thermal wakups to threads Steven Rostedt
2015-03-12 19:13   ` Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 32/39] lockdep: selftest: fix warnings due to missing PREEMPT_RT conditionals Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 33/39] fs/aio: simple simple work Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 34/39] timers: Track total number of timers in list Steven Rostedt
2015-03-12 19:13 ` Steven Rostedt [this message]
2015-03-12 19:13 ` [PATCH RT 36/39] timers: Reduce future __run_timers() latency for newly emptied list Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 37/39] timers: Reduce future __run_timers() latency for first add to empty list Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 38/39] staging: Mark rtl8821ae as broken Steven Rostedt
2015-03-12 19:13 ` [PATCH RT 39/39] Linux 3.14.34-rt32-rc1 Steven Rostedt
2015-03-13  4:49 ` [PATCH RT 00/39] " Mike Galbraith
2015-03-13 13:50   ` Steven Rostedt
2015-03-13 15:11   ` Steven Rostedt
2015-03-13 15:11     ` Steven Rostedt
2015-03-13 15:24     ` Steven Rostedt
2015-03-13 11:01 ` Sebastian Andrzej Siewior
2015-03-13 11:33 ` Sebastian Andrzej Siewior
2015-03-16 13:59 ` Sebastian Andrzej Siewior
2015-03-16 14:02   ` Steven Rostedt
2015-03-16 14:10     ` Sebastian Andrzej Siewior

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