From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: [PATCH -mm 2/3] Freezer: Use wait queue instead of busy looping Date: Wed, 1 Aug 2007 23:32:48 +0200 Message-ID: <200708012332.48798.rjw@sisk.pl> References: <200708012328.23939.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-2" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <200708012328.23939.rjw@sisk.pl> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: Andrew Morton Cc: pm list , Nigel Cunningham , LKML , Pavel Machek , Oleg Nesterov List-Id: linux-pm@vger.kernel.org From: Rafael J. Wysocki Use the observation that try_to_freeze_tasks() need not loop while waitin= g 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 freezable try_to_freeze_tasks() can go to sleep and wait until at least o= ne task enters the refrigerator. =A0The first task that does it wakes up try_to_freeze_tasks() and the procedure is repeated. =A0If the refrigerat= or 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 freezing tasks are waiting for I/O to complete. Signed-off-by: Rafael J. Wysocki Acked-by: Pavel Machek --- kernel/power/process.c | 34 +++++++++++++++++++++++++++++++++- 1 file changed, 33 insertions(+), 1 deletion(-) Index: linux-2.6.23-rc1/kernel/power/process.c =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --- linux-2.6.23-rc1.orig/kernel/power/process.c 2007-07-31 21:58:32.0000= 00000 +0200 +++ linux-2.6.23-rc1/kernel/power/process.c 2007-07-31 23:00:43.000000000= +0200 @@ -19,6 +19,12 @@ */ #define TIMEOUT (20 * HZ) =20 +/* + * Time to wait until one or more tasks enter the refrigerator after sen= ding + * freeze requests to them. + */ +#define WAIT_TIME (HZ / 5) + #define FREEZER_KERNEL_THREADS 0 #define FREEZER_USER_SPACE 1 =20 @@ -43,6 +49,18 @@ static inline void frozen_process(void) clear_freeze_flag(current); } =20 +/* + * Wait queue head used by try_to_freeze_tasks() to wait for tasks to en= ter the + * refrigerator. + */ +static DECLARE_WAIT_QUEUE_HEAD(refrigerator_waitq); + +/* + * Used to notify try_to_freeze_tasks() that the refrigerator has been e= ntered + * by a task. + */ +static int refrigerator_called; + /* Refrigerator is place where frozen processes are stored :-). */ void refrigerator(void) { @@ -58,6 +76,10 @@ void refrigerator(void) task_unlock(current); return; } + + refrigerator_called =3D 1; + wake_up(&refrigerator_waitq); + save =3D current->state; pr_debug("%s entered refrigerator\n", current->comm); =20 @@ -170,6 +192,7 @@ static int try_to_freeze_tasks(int freez unsigned int todo; =20 end_time =3D jiffies + TIMEOUT; + refrigerator_called =3D 0; do { todo =3D 0; read_lock(&tasklist_lock); @@ -189,7 +212,16 @@ static int try_to_freeze_tasks(int freez todo++; } while_each_thread(g, p); read_unlock(&tasklist_lock); - yield(); /* Yield is okay here */ + + if (todo) { + unsigned long ret; + + ret =3D wait_event_timeout(refrigerator_waitq, + refrigerator_called, WAIT_TIME); + if (ret) + refrigerator_called =3D 0; + } + if (time_after(jiffies, end_time)) break; } while (todo);