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Date: Thu, 19 May 2011 11:41:53 +0200
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: yong.zhang0@...il.com, paulmck@...ux.vnet.ibm.com, oleg@...hat.com,
linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
mingo@...e.hu, lizf@...fujitsu.com, miaox@...fujitsu.com
Subject: Re: [PATCH v2 1/2] rcu: don't bind offline cpu
On Thu, 2011-05-19 at 17:50 +0900, KOSAKI Motohiro wrote:
> I'm sorry. Please give me a bit time.
N/P, as I've already found out CPU_STARTING isn't a suitable location
either.
How about something like the below...
---
Subject: rcu: Remove waitqueue usage for cpu,node and boost kthreads
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Thu May 19 11:27:39 CEST 2011
Since wait-queue usage is inconsistent (node) and generally not needed
since we know exactly which thread to wake, rip it out.
The problem is that wake_up() only issues an actual wake-up when there's
a thread waiting on the queue which means we need an extra, explicit,
wakeup to kick-start the kthread itself (they're born sleeping).
Now, since we already know which exact thread we want to wake up,
there's not point really in enqueing it on a waitqueue. So provide Paul
with a nice rcu_wait() macro to replace wait_event_interruptible() with
and rip out all the waitqueue stuff.
This moves us to an explicit, unconditional, wake_up_process() which can
be used to wake us from both conditions.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
Index: linux-2.6/kernel/rcutree.c
===================================================================
--- linux-2.6.orig/kernel/rcutree.c
+++ linux-2.6/kernel/rcutree.c
@@ -94,7 +94,6 @@ static DEFINE_PER_CPU(struct task_struct
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
-static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
DEFINE_PER_CPU(char, rcu_cpu_has_work);
static char rcu_kthreads_spawnable;
@@ -1475,7 +1474,7 @@ static void invoke_rcu_cpu_kthread(void)
local_irq_restore(flags);
return;
}
- wake_up(&__get_cpu_var(rcu_cpu_wq));
+ wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
local_irq_restore(flags);
}
@@ -1598,14 +1597,12 @@ static int rcu_cpu_kthread(void *arg)
unsigned long flags;
int spincnt = 0;
unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
- wait_queue_head_t *wqp = &per_cpu(rcu_cpu_wq, cpu);
char work;
char *workp = &per_cpu(rcu_cpu_has_work, cpu);
for (;;) {
*statusp = RCU_KTHREAD_WAITING;
- wait_event_interruptible(*wqp,
- *workp != 0 || kthread_should_stop());
+ rcu_wait(*workp != 0 || kthread_should_stop());
local_bh_disable();
if (rcu_cpu_kthread_should_stop(cpu)) {
local_bh_enable();
@@ -1656,7 +1653,6 @@ static int __cpuinit rcu_spawn_one_cpu_k
per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
per_cpu(rcu_cpu_kthread_task, cpu) = t;
- wake_up_process(t);
sp.sched_priority = RCU_KTHREAD_PRIO;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
return 0;
@@ -1679,7 +1675,7 @@ static int rcu_node_kthread(void *arg)
for (;;) {
rnp->node_kthread_status = RCU_KTHREAD_WAITING;
- wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0);
+ rcu_wait(rnp->wakemask != 0);
rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
raw_spin_lock_irqsave(&rnp->lock, flags);
mask = rnp->wakemask;
@@ -1764,7 +1760,6 @@ static int __cpuinit rcu_spawn_one_node_
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->node_kthread_task = t;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
- wake_up_process(t);
sp.sched_priority = 99;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
}
@@ -1781,21 +1776,16 @@ static int __init rcu_spawn_kthreads(voi
rcu_kthreads_spawnable = 1;
for_each_possible_cpu(cpu) {
- init_waitqueue_head(&per_cpu(rcu_cpu_wq, cpu));
per_cpu(rcu_cpu_has_work, cpu) = 0;
if (cpu_online(cpu))
(void)rcu_spawn_one_cpu_kthread(cpu);
}
rnp = rcu_get_root(rcu_state);
- init_waitqueue_head(&rnp->node_wq);
- rcu_init_boost_waitqueue(rnp);
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
- if (NUM_RCU_NODES > 1)
- rcu_for_each_leaf_node(rcu_state, rnp) {
- init_waitqueue_head(&rnp->node_wq);
- rcu_init_boost_waitqueue(rnp);
+ if (NUM_RCU_NODES > 1) {
+ rcu_for_each_leaf_node(rcu_state, rnp)
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
- }
+ }
return 0;
}
early_initcall(rcu_spawn_kthreads);
Index: linux-2.6/kernel/rcutree.h
===================================================================
--- linux-2.6.orig/kernel/rcutree.h
+++ linux-2.6/kernel/rcutree.h
@@ -28,6 +28,17 @@
#include <linux/cpumask.h>
#include <linux/seqlock.h>
+#define rcu_wait(cond) \
+do { \
+ for (;;) { \
+ set_current_state(TASK_INTERRUPTIBLE); \
+ if (cond) \
+ break; \
+ schedule(); \
+ } \
+ __set_current_state(TASK_RUNNING); \
+} while (0)
+
/*
* Define shape of hierarchy based on NR_CPUS and CONFIG_RCU_FANOUT.
* In theory, it should be possible to add more levels straightforwardly.
@@ -157,9 +168,6 @@ struct rcu_node {
struct task_struct *boost_kthread_task;
/* kthread that takes care of priority */
/* boosting for this rcu_node structure. */
- wait_queue_head_t boost_wq;
- /* Wait queue on which to park the boost */
- /* kthread. */
unsigned int boost_kthread_status;
/* State of boost_kthread_task for tracing. */
unsigned long n_tasks_boosted;
@@ -186,9 +194,6 @@ struct rcu_node {
/* kthread that takes care of this rcu_node */
/* structure, for example, awakening the */
/* per-CPU kthreads as needed. */
- wait_queue_head_t node_wq;
- /* Wait queue on which to park the per-node */
- /* kthread. */
unsigned int node_kthread_status;
/* State of node_kthread_task for tracing. */
} ____cacheline_internodealigned_in_smp;
@@ -443,7 +448,6 @@ static void __cpuinit rcu_preempt_init_p
static void rcu_preempt_send_cbs_to_online(void);
static void __init __rcu_init_preempt(void);
static void rcu_needs_cpu_flush(void);
-static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
cpumask_var_t cm);
Index: linux-2.6/kernel/rcutree_plugin.h
===================================================================
--- linux-2.6.orig/kernel/rcutree_plugin.h
+++ linux-2.6/kernel/rcutree_plugin.h
@@ -1196,8 +1196,7 @@ static int rcu_boost_kthread(void *arg)
for (;;) {
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
- wait_event_interruptible(rnp->boost_wq, rnp->boost_tasks ||
- rnp->exp_tasks);
+ rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
more2boost = rcu_boost(rnp);
if (more2boost)
@@ -1275,14 +1274,6 @@ static void rcu_preempt_boost_start_gp(s
}
/*
- * Initialize the RCU-boost waitqueue.
- */
-static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp)
-{
- init_waitqueue_head(&rnp->boost_wq);
-}
-
-/*
* Create an RCU-boost kthread for the specified node if one does not
* already exist. We only create this kthread for preemptible RCU.
* Returns zero if all is well, a negated errno otherwise.
@@ -1306,7 +1297,6 @@ static int __cpuinit rcu_spawn_one_boost
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->boost_kthread_task = t;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
- wake_up_process(t);
sp.sched_priority = RCU_KTHREAD_PRIO;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
return 0;
@@ -1328,10 +1318,6 @@ static void rcu_preempt_boost_start_gp(s
{
}
-static void __init rcu_init_boost_waitqueue(struct rcu_node *rnp)
-{
-}
-
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp,
int rnp_index)
--
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