On 11/12, Peter Zijlstra wrote:
>
> On Tue, Nov 12, 2013 at 02:21:39PM -0000, David Laight wrote:
> > Shame there isn't a process flag to indicate that the process
> > will sleep uninterruptibly and that it doesn't matter.
> > So don't count to the load average and don't emit a warning
> > if it has been sleeping for a long time.
>
> A process flag wouldn't work, because the task could block waiting for
> actual work to complete in other sleeps.
>
> However, we could do something like the below; which would allow us
> writing things like:
>
> (void)___wait_event(*sk_sleep(sk),
> sock_writeable(sk) || kthread_should_stop(),
> TASK_UNINTERRUPTIBLE | TASK_IDLE, 0, 0,
> schedule());
>
> Marking the one wait-for-more-work as TASK_IDLE such that it doesn't
> contribute to the load avg.
Agreed, I thought about additional bit too.
> static const char * const task_state_array[] = {
> - "R (running)", /* 0 */
> - "S (sleeping)", /* 1 */
> - "D (disk sleep)", /* 2 */
> - "T (stopped)", /* 4 */
> - "t (tracing stop)", /* 8 */
> - "Z (zombie)", /* 16 */
> - "X (dead)", /* 32 */
> - "x (dead)", /* 64 */
> - "K (wakekill)", /* 128 */
> - "W (waking)", /* 256 */
> - "P (parked)", /* 512 */
> + "R (running)", /* 0 */
> + "S (sleeping)", /* 1 */
> + "D (disk sleep)", /* 2 */
> + "T (stopped)", /* 4 */
> + "t (tracing stop)", /* 8 */
> + "Z (zombie)", /* 16 */
> + "X (dead)", /* 32 */
> + "x (dead)", /* 64 */
> + "K (wakekill)", /* 128 */
> + "W (waking)", /* 256 */
> + "P (parked)", /* 512 */
> + "I (idle)", /* 1024 */
> };
but I am not sure about what /proc/ should report in this case...
> #define task_contributes_to_load(task) \
> ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
> - (task->flags & PF_FROZEN) == 0)
> + (task->flags & PF_FROZEN) == 0 && \
> + (task->state & TASK_IDLE) == 0)
perhaps
(task->state & (TASK_UNINTERRUPTIBLE | TASK_IDLE)) ==
TASK_UNINTERRUPTIBLE
can save an insn.
I am also wondering if it makes any sense to turn PF_FROZEN into
TASK_FROZEN, something like (incomplete, probably racy) patch below.
Note that it actually adds the new state, not the the qualifier.
Oleg.
--- x/include/linux/freezer.h
+++ x/include/linux/freezer.h
@@ -23,7 +23,7 @@ extern unsigned int freeze_timeout_msecs
*/
static inline bool frozen(struct task_struct *p)
{
- return p->flags & PF_FROZEN;
+ return p->state & TASK_FROZEN;
}
extern bool freezing_slow_path(struct task_struct *p);
--- x/kernel/freezer.c
+++ x/kernel/freezer.c
@@ -57,16 +57,13 @@ bool __refrigerator(bool check_kthr_stop
pr_debug("%s entered refrigerator\n", current->comm);
for (;;) {
- set_current_state(TASK_UNINTERRUPTIBLE);
-
spin_lock_irq(&freezer_lock);
- current->flags |= PF_FROZEN;
- if (!freezing(current) ||
- (check_kthr_stop && kthread_should_stop()))
- current->flags &= ~PF_FROZEN;
+ if (freezing(current) &&
+ !(check_kthr_stop && kthread_should_stop()))
+ set_current_state(TASK_FROZEN);
spin_unlock_irq(&freezer_lock);
- if (!(current->flags & PF_FROZEN))
+ if (!(current->state & TASK_FROZEN))
break;
was_frozen = true;
schedule();
@@ -148,8 +145,7 @@ void __thaw_task(struct task_struct *p)
* refrigerator.
*/
spin_lock_irqsave(&freezer_lock, flags);
- if (frozen(p))
- wake_up_process(p);
+ try_to_wake_up(p, TASK_FROZEN, 0);
spin_unlock_irqrestore(&freezer_lock, flags);
}
--
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