On Sat 15-03-14 13:22:53, dbasehore . wrote:

Resurrecting this for further discussion about the root of the problem.

mod_delayed_work_if_later addresses the problem one way, but the
problem is still there for mod_delayed_work.

  But flusher works care about only that one way, don't they? We always
want the flushing work to execute at min(timer so far, new time target). So
for that mod_delayed_work_if_later() works just fine.

I think we could take
another approach that doesn't modify the API, but still addresses
(most of) the problem.

mod_delayed_work currently removes a work item from a workqueue if it
is on it. Correct me if I'm wrong, but I don't think that this is
necessarily required for mod_delayed_work to have the current
behavior. We should be able to set the timer while a delayed_work is
currently on a workqueue. If the delayed_work is still on the
workqueue when the timer goes off, everything is fine. If it has left
the workqueue, we can queue it again.

  But here you are relying on the fact that flusher works always want the
work to be executed immediately (i.e., they will be queued), or after some
fixed time T. So I agree what you suggest will work but changing the API as
Tejun described seems cleaner to me.

								Honza

On Wed, Feb 19, 2014 at 11:01 AM, Tejun Heo [off-list ref] wrote:

quoted

Hello, Jan.

On Wed, Feb 19, 2014 at 10:27:31AM +0100, Jan Kara wrote:

quoted

  You are the workqueue expert so you may know better ;) But the way I
understand it is that queue_delayed_work() does nothing if the timer is
already running. Since we queue flusher work to run either immediately or
after dirty_writeback_interval we are safe to run queue_delayed_work()
whenever we want it to run after dirty_writeback_interval and
mod_delayed_work() whenever we want to run it immediately.

Ah, okay, so it's always mod on immediate and queue on delayed.  Yeah,
that should work.

quoted

But it's subtle and some interface where we could say queue delayed work
after no later than X would be easier to grasp.

Yeah, I think it'd be better if we had something like
mod_delayed_work_if_later().  Hmm...

Thanks.

--
tejun

-- 
Jan Kara [off-list ref]
SUSE Labs, CR

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