Sleeping in workqueues

[Arun Sudhilal]

Hello Tobias,

On Sun, Feb 12, 2017 at 7:15 PM, Tobias FItschen
<tobias.fitschen at campus.tu-berlin.de> wrote:
> Hello people,
>
> I have a question regarding workqueues. I know it's possible to sleep in
> workqueue routines. Does that mean I can use:

What it means is that you are safe to use any sub routines which may
sleep or which will sleep.

>
> 1. "set_current_state(TASK_INTERRUPTIBLE);" get the the task with
> "current" and pass it to a other task and then call "schedule();" in a
> workqueue routine and at a different place (perhaps another workqueue
> routine) use wake_up_process(task)" ?
>
> 2. initialize completions in a workqueue routine and call complete() in
> a different workqueue routine?
>
> I tried it in a simple example setup and both worked. I just want to

completion variables are written to hide the complexity of using
set_current_state and related functions to make a thread sleep. It
basically enables driver authors to reuse the same code for
sleep/wake.
At the heart of it, its all the same. My recommendation is to use completion.

> make sure that was not just by accident. As I understand it a work item
> is executed on a worker, which is a unique process, but I also know that
> there are exceptions, e.g. I can not copy to or from user space in a
> workqueue routine. Also I don't know if a worker "sticks" with the
> current work item until it is completed or can execute multiple work
> items at the "same" time.

Yes a kworker sticks with current work item until it is completed. If
a work item currently executed by a worker met with a sleep, another
kworkers are used to process the other pending work items.

Regards,
Arun

>
> 3. In case completions and schedule()/wakeup() work, I would also like
> to know, which has the better performance.
>
> Thanks a lot already!
>
> Tobias
>
>
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