On Tue 2016-01-12 08:20:21, Jacob Pan wrote:

On Tue, 12 Jan 2016 11:11:29 +0100
Petr Mladek [off-list ref] wrote:

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BTW: I wonder if the original code correctly handle freezing after
the schedule_timeout(). It does not call try_to_freeze()
there and the forced idle states might block freezing.
I think that the small overhead of kthread works is worth
solving such bugs. It makes it easier to maintain these
sleeping states.  

it is in a while loop, so try_to_freeze() gets called. Am I missing
something?  

But it might take some time until try_to_freeze() is called.
If I get it correctly. try_to_freeze_tasks() wakes freezable
tasks to get them into the fridge. If clamp_thread() is waken
from that schedule_timeout_interruptible(), it still might inject
the idle state before calling try_to_freeze(). It means that freezer
needs to wait "quite" some time until the kthread ends up in the
fridge.

Hmm, even my conversion does not solve this entirely. We might
need to call freezing(current) in the

   while (time_before(jiffies, target_jiffies)) {

cycle. And break injecting the idle state when freezing is requested.

The injection time for each period is very short, default 6ms. While on
the other side the default freeze timeout is 20 sec. So I think task
freeze can wait :)
i.e.
unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;

You are right. And it does not make sense to add an extra
freezer-specific code if not really necessary.

Otherwise, I will keep the conversion into the kthread worker as is
for now. Please, let me know if you are strongly against the split
into the two works.


Best Regards,
Petr