lkml.org 
[lkml]   [2011]   [Jun]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC 1/1] workqueue: Add mod_delayed_work()
Hello,

On Fri, Jun 24, 2011 at 07:27:37PM -0300, Gustavo F. Padovan wrote:
> mod_delayed_work() updates a timer if the work is pending otherwise calls
> queue_delayed_work_on() to queue the work with the specified delay.
>
> Call cancel_delayed_work_sync() and then queue_delayed_work() again to
> change a timer's delays is too expensive (and requires process context).
> Istead we call mod_delayed_work() to only modify the timer's timeout.

Yes, this part of the interface is lacking. It might be best to
modify queue_delayed_work() to adjust the timer according to the new
timeout but we would need to audit the current users to make sure
nothing breaks and I agree introducing a new function probably makes
sense.

> +int mod_delayed_work(struct workqueue_struct *wq,
> + struct delayed_work *dwork, unsigned long delay)
> +{
> + struct timer_list *timer = &dwork->timer;
> + struct work_struct *work = &dwork->work;
> +
> + if (!test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
> + return queue_delayed_work_on(-1, wq, dwork, delay);
> +
> + BUG_ON(!timer_pending(timer));
> +
> + mod_timer(timer, jiffies + delay);
> +
> + return 0;
> +}

But I think the current implementation is as it is because modifying
delayed work safely wasn't very simple. The above code is broken in
multiple ways - a delayed work could be pending without timer pending,
and timer may expire after test_bit() but before the rest of the code.

I haven't thought about it too hard but think it would require the
timer sync part of __cancel_work_timer() (sans wait_on_work()) to get
it correctly. Care to delve into it?

Thanks.

--
tejun


\
 
 \ /
  Last update: 2011-06-25 13:45    [W:0.043 / U:1.872 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site