lkml.org 
[lkml]   [2008]   [Feb]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] simplify cpu_hotplug_begin()/put_online_cpus()
cpu_hotplug_begin() must be always called under cpu_add_remove_lock, this means
that only one process can be cpu_hotplug.active_writer. So we don't need the
cpu_hotplug.writer_queue, we can wake up the ->active_writer directly.

Also, fix the comment.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 25/kernel/cpu.c~1_CPU_HP_LOCK 2008-02-15 16:59:17.000000000 +0300
+++ 25/kernel/cpu.c 2008-02-16 18:36:37.000000000 +0300
@@ -33,17 +33,13 @@ static struct {
* an ongoing cpu hotplug operation.
*/
int refcount;
- wait_queue_head_t writer_queue;
} cpu_hotplug;

-#define writer_exists() (cpu_hotplug.active_writer != NULL)
-
void __init cpu_hotplug_init(void)
{
cpu_hotplug.active_writer = NULL;
mutex_init(&cpu_hotplug.lock);
cpu_hotplug.refcount = 0;
- init_waitqueue_head(&cpu_hotplug.writer_queue);
}

#ifdef CONFIG_HOTPLUG_CPU
@@ -65,11 +61,8 @@ void put_online_cpus(void)
if (cpu_hotplug.active_writer == current)
return;
mutex_lock(&cpu_hotplug.lock);
- cpu_hotplug.refcount--;
-
- if (unlikely(writer_exists()) && !cpu_hotplug.refcount)
- wake_up(&cpu_hotplug.writer_queue);
-
+ if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
+ wake_up_process(cpu_hotplug.active_writer);
mutex_unlock(&cpu_hotplug.lock);

}
@@ -98,8 +91,8 @@ void cpu_maps_update_done(void)
* Note that during a cpu-hotplug operation, the new readers, if any,
* will be blocked by the cpu_hotplug.lock
*
- * Since cpu_maps_update_begin is always called after invoking
- * cpu_maps_update_begin, we can be sure that only one writer is active.
+ * Since cpu_hotplug_begin() is always called after invoking
+ * cpu_maps_update_begin(), we can be sure that only one writer is active.
*
* Note that theoretically, there is a possibility of a livelock:
* - Refcount goes to zero, last reader wakes up the sleeping
@@ -115,19 +108,16 @@ void cpu_maps_update_done(void)
*/
static void cpu_hotplug_begin(void)
{
- DECLARE_WAITQUEUE(wait, current);
-
- mutex_lock(&cpu_hotplug.lock);
-
cpu_hotplug.active_writer = current;
- add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait);
- while (cpu_hotplug.refcount) {
- set_current_state(TASK_UNINTERRUPTIBLE);
+
+ for (;;) {
+ mutex_lock(&cpu_hotplug.lock);
+ if (likely(!cpu_hotplug.refcount))
+ break;
+ __set_current_state(TASK_UNINTERRUPTIBLE);
mutex_unlock(&cpu_hotplug.lock);
schedule();
- mutex_lock(&cpu_hotplug.lock);
}
- remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);
}

static void cpu_hotplug_done(void)


\
 
 \ /
  Last update: 2008-02-16 18:23    [W:0.043 / U:0.388 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site