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Date: Tue, 28 Jan 2014 13:57:20 +0600
From: Rakib Mullick <rakib.mullick@...il.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>
Subject: Do we really need curr_target in signal_struct ?
I was wondering what might be the possible use of curr_target in signal_struct (atleast,
it's not doing what it's comment says). Also, I'm not seeing any real use of it except
in kernel/signal.c::complete_signal() where it's use as loop breaking condition in thread's
list traversing. As an alternative of using curr_target we can use get_nr_thread() count
to get # of threads in a group and can remove curr_target completely. This will also help
us to get rid from overhead of maintaining ->curr_target at fork()/exit() path. Below is
rough patch, I can prepare a good one if everyone agrees.
Or we really need it?
---
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 485234d..1fd65b7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -554,7 +554,7 @@ struct signal_struct {
wait_queue_head_t wait_chldexit; /* for wait4() */
/* current thread group signal load-balancing target: */
- struct task_struct *curr_target;
+ //struct task_struct *curr_target;
/* shared signal handling: */
struct sigpending shared_pending;
diff --git a/kernel/exit.c b/kernel/exit.c
index 1e77fc6..4a2cf37 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -113,8 +113,8 @@ static void __exit_signal(struct task_struct *tsk)
if (sig->notify_count > 0 && !--sig->notify_count)
wake_up_process(sig->group_exit_task);
- if (tsk == sig->curr_target)
- sig->curr_target = next_thread(tsk);
+ //if (tsk == sig->curr_target)
+ // sig->curr_target = next_thread(tsk);
/*
* Accumulate here the counters for all threads but the
* group leader as they die, so they can be added into
diff --git a/kernel/fork.c b/kernel/fork.c
index 2f11bbe..8de4928 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1041,7 +1041,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
init_waitqueue_head(&sig->wait_chldexit);
- sig->curr_target = tsk;
+ //sig->curr_target = tsk;
init_sigpending(&sig->shared_pending);
INIT_LIST_HEAD(&sig->posix_timers);
diff --git a/kernel/signal.c b/kernel/signal.c
index 940b30e..1a1280a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -945,6 +945,7 @@ static void complete_signal(int sig, struct task_struct *p, int group)
{
struct signal_struct *signal = p->signal;
struct task_struct *t;
+ int i;
/*
* Now find a thread we can wake up to take the signal off the queue.
@@ -961,21 +962,16 @@ static void complete_signal(int sig, struct task_struct *p, int group)
*/
return;
else {
- /*
- * Otherwise try to find a suitable thread.
- */
- t = signal->curr_target;
- while (!wants_signal(sig, t)) {
+ i = get_nr_threads(p);
+ t = p;
+ do {
+ --i;
t = next_thread(t);
- if (t == signal->curr_target)
- /*
- * No thread needs to be woken.
- * Any eligible threads will see
- * the signal in the queue soon.
- */
+ if (!i)
return;
- }
- signal->curr_target = t;
+ } while (!wants_signal(sig, t));
+
+ //signal->curr_target = t;
}
/*
--
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