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Date: Mon, 08 Feb 2010 11:00:45 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: highguy@...il.com
Cc: mingo@...e.hu, linux-kernel@...r.kernel.org,
torvalds@...ux-foundation.org, efault@....de, andrea@...e.de,
tglx@...utronix.de, akpm@...ux-foundation.org,
Tejun Heo <tj@...nel.org>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH] PERF_COUNT_SW_RUNNABLE_TASKS: measure and act
upon parallellism
On Sun, 2010-02-07 at 12:30 +0100, highguy@...il.com wrote:
> Here's an initial RFC patch for the parallallism
> events for perf_events.
OK, so you managed to rub me totally the wrong way with posting this
yesterday:
- you send me each patch twice
- you used the horrible git sendmail default of --chain-reply-to
(some day I'll write a script that will detect and auto-bounce
series sent to me like that)
- you failed to provide a changelog for any of the patches
- some subjects were long enough to be a changelog
Please don't do that again ;-)
Anyway, it did get me thinking, how about something like the below?
(compile tested only, we probably want a different name than CLONE_SEM,
but I failed at coming up with anything better, CLONE_FRED?)
---
include/linux/sched.h | 11 ++++++++++
kernel/exit.c | 5 ++++
kernel/fork.c | 24 ++++++++++++++++++++++
kernel/sched.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++-
4 files changed, 92 insertions(+), 1 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b1b8d84..580c623 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -9,6 +9,7 @@
#define CLONE_FS 0x00000200 /* set if fs info shared between processes */
#define CLONE_FILES 0x00000400 /* set if open files shared between processes */
#define CLONE_SIGHAND 0x00000800 /* set if signal handlers and blocked signals shared */
+#define CLONE_SEM 0x00001000 /* set if */
#define CLONE_PTRACE 0x00002000 /* set if we want to let tracing continue on the child too */
#define CLONE_VFORK 0x00004000 /* set if the parent wants the child to wake it up on mm_release */
#define CLONE_PARENT 0x00008000 /* set if we want to have the same parent as the cloner */
@@ -1214,6 +1215,13 @@ struct sched_rt_entity {
struct rcu_node;
+struct task_sem {
+ raw_spinlock_t lock;
+ unsigned int count;
+ struct list_head wait_list;
+ atomic_t ref;
+};
+
struct task_struct {
volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */
void *stack;
@@ -1235,6 +1243,9 @@ struct task_struct {
struct sched_entity se;
struct sched_rt_entity rt;
+ struct task_sem *sem;
+ struct list_head sem_waiter;
+
#ifdef CONFIG_PREEMPT_NOTIFIERS
/* list of struct preempt_notifier: */
struct hlist_head preempt_notifiers;
diff --git a/kernel/exit.c b/kernel/exit.c
index 546774a..f8b9ab3 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -991,6 +991,11 @@ NORET_TYPE void do_exit(long code)
*/
perf_event_exit_task(tsk);
+ if (unlikely(tsk->sem) && atomic_dec_and_test(&tsk->sem->ref)) {
+ kfree(tsk->sem);
+ tsk->sem = NULL;
+ }
+
exit_notify(tsk, group_dead);
#ifdef CONFIG_NUMA
mpol_put(tsk->mempolicy);
diff --git a/kernel/fork.c b/kernel/fork.c
index f88bd98..cea102c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -989,6 +989,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
+ if ((clone_flags & (CLONE_VFORK|CLONE_SEM)) == (CLONE_VFORK|CLONE_SEM))
+ return ERR_PTR(-EINVAL);
+
/*
* Thread groups must share signals as well, and detached threads
* can only be started up within the thread group.
@@ -1023,6 +1026,27 @@ static struct task_struct *copy_process(unsigned long clone_flags,
if (!p)
goto fork_out;
+ if (clone_flags & CLONE_SEM) {
+ INIT_LIST_HEAD(&p->sem_waiter);
+ if (!current->sem) {
+ struct task_sem *sem =
+ kmalloc(sizeof(struct task_sem), GFP_KERNEL);
+
+ if (!sem)
+ goto bad_fork_free;
+
+ raw_spin_lock_init(&sem->lock);
+ sem->count = 0; /* current is running */
+ INIT_LIST_HEAD(&sem->wait_list);
+ atomic_set(&sem->ref, 2);
+
+ current->sem = sem;
+ p->sem = sem;
+ } else
+ atomic_inc(¤t->sem->ref);
+ } else if (current->sem)
+ p->sem = NULL;
+
ftrace_graph_init_task(p);
rt_mutex_init_task(p);
diff --git a/kernel/sched.c b/kernel/sched.c
index de9f9d4..9cd6144 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2247,6 +2247,48 @@ void task_oncpu_function_call(struct task_struct *p,
preempt_enable();
}
+static void task_up(struct rq *rq, struct task_struct *p)
+{
+ struct task_struct *waiter = NULL;
+ struct task_sem *sem = p->sem;
+
+ raw_spin_lock(&sem->lock);
+ sem->count++;
+ if (sem->count > 0 && !list_empty(&sem->wait_list)) {
+ waiter = list_first_entry(&sem->wait_list,
+ struct task_struct, sem_waiter);
+
+ list_del_init(&waiter->sem_waiter);
+ }
+ raw_spin_unlock(&sem->lock);
+
+ if (waiter) {
+ raw_spin_unlock(&rq->lock);
+ wake_up_process(waiter);
+ raw_spin_lock(&rq->lock);
+ }
+}
+
+static int task_down(struct task_struct *p)
+{
+ struct task_sem *sem = p->sem;
+ int ret = 0;
+
+ raw_spin_lock(&sem->lock);
+ if (sem->count > 0) {
+ sem->count--;
+ } else {
+ WARN_ON_ONCE(!list_empty(&p->sem_waiter));
+
+ list_add_tail(&p->sem_waiter, &sem->wait_list);
+ __set_task_state(p, TASK_UNINTERRUPTIBLE);
+ ret = 1;
+ }
+ raw_spin_unlock(&sem->lock);
+
+ return ret;
+}
+
#ifdef CONFIG_SMP
static int select_fallback_rq(int cpu, struct task_struct *p)
{
@@ -2357,7 +2399,12 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
#ifdef CONFIG_SMP
if (unlikely(task_running(rq, p)))
goto out_activate;
+#endif
+ if (unlikely(p->sem) && task_down(p))
+ goto out;
+
+#ifdef CONFIG_SMP
/*
* In order to handle concurrent wakeups and release the rq->lock
* we put the task in TASK_WAKING state.
@@ -3671,8 +3718,12 @@ need_resched_nonpreemptible:
if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
if (unlikely(signal_pending_state(prev->state, prev)))
prev->state = TASK_RUNNING;
- else
+ else {
deactivate_task(rq, prev, 1);
+
+ if (unlikely(prev->sem))
+ task_up(rq, prev);
+ }
switch_count = &prev->nvcsw;
}
--
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