From: Rafael J. Wysocki From: Rafael J. Wysocki Use the observation that try_to_freeze_tasks() need not loop while waiting for the freezing tasks to enter the refrigerator and make it use a wait queue. The idea is that after sending freeze requests to the tasks regarded as From: Rafael J. Wysocki freezable try_to_freeze_tasks() can go to sleep and wait until at least one task enters the refrigerator.  The first task that does it wakes up try_to_freeze_tasks() and the procedure is repeated.  If the refrigerator is not entered by any tasks before TIMEOUT expires, the freezing of tasks fails. This way, try_to_freeze_tasks() doesn't occupy the CPU unnecessarily when some From: Rafael J. Wysocki freezing tasks are waiting for I/O to complete. Signed-off-by: Rafael J. Wysocki Cc: Pavel Machek Signed-off-by: Andrew Morton --- kernel/power/process.c | 26 +++++++++++++++++++++++++- 1 files changed, 25 insertions(+), 1 deletion(-) diff -puN kernel/power/process.c~freezer-use-wait-queue-instead-of-busy-looping kernel/power/process.c --- a/kernel/power/process.c~freezer-use-wait-queue-instead-of-busy-looping +++ a/kernel/power/process.c @@ -19,6 +19,12 @@ */ #define TIMEOUT (20 * HZ) +/* + * Time to wait until one or more tasks enter the refrigerator after sending + * freeze requests to them. + */ +#define WAIT_TIME (HZ / 5) + #define FREEZER_KERNEL_THREADS 0 #define FREEZER_USER_SPACE 1 @@ -43,6 +49,12 @@ static inline void frozen_process(void) clear_freeze_flag(current); } +/* + * Wait queue head used by try_to_freeze_tasks() to wait for tasks to enter the + * refrigerator. + */ +static DECLARE_WAIT_QUEUE_HEAD(refrigerator_waitq); + /* Refrigerator is place where frozen processes are stored :-). */ void refrigerator(void) { @@ -58,6 +70,9 @@ void refrigerator(void) task_unlock(current); return; } + + wake_up(&refrigerator_waitq); + save = current->state; pr_debug("%s entered refrigerator\n", current->comm); @@ -171,6 +186,10 @@ static int try_to_freeze_tasks(int freez end_time = jiffies + TIMEOUT; do { + DEFINE_WAIT(wait); + + add_wait_queue(&refrigerator_waitq, &wait); + todo = 0; read_lock(&tasklist_lock); do_each_thread(g, p) { @@ -189,7 +208,12 @@ static int try_to_freeze_tasks(int freez todo++; } while_each_thread(g, p); read_unlock(&tasklist_lock); - yield(); /* Yield is okay here */ + + set_current_state(TASK_UNINTERRUPTIBLE); + if (todo && !list_empty_careful(&wait.task_list)) + schedule_timeout(WAIT_TIME); + finish_wait(&refrigerator_waitq, &wait); + if (time_after(jiffies, end_time)) break; } while (todo); _