Re: Ordering / preemption of work in a workqueue preempt?
anish singh <[email protected]>
| Newsgroups | gmane.linux.newbie,gmane.linux.kernel.kernelnewbies |
|---|---|
| Message-ID | <CAK7N6vov2dKhK3hfn6wPHc+ELQavjho_ypALVts4Ajs=J0U1WA@mail.gmail.com> |
On Mon, Nov 18, 2013 at 10:20 PM, Arun KS <[email protected]> wrote: > Hi Rajat, > > On Fri, Nov 15, 2013 at 8:46 PM, Rajat Jain <[email protected]> wrote: >> Hi, >> >> I have a single work queue, on which I have scheduled a worker function [using queue_work(wq, fn)] in interrupt context. >> >> I get the interrupt twice before the work queue gets a chance to run, and hence the same function will get queued twice (with different private context - arguments etc) which is fine and expected. > > You got it wrong here. > > bool queue_work_on(int cpu, struct workqueue_struct *wq, > struct work_struct *work) > { > bool ret = false; > unsigned long flags; > > local_irq_save(flags); > > if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) { > __queue_work(cpu, wq, work); > ret = true; > } > > local_irq_restore(flags); > return ret; > } > EXPORT_SYMBOL(queue_work_on); > > If you look at function queue_work_on, the function returns > immediately if WORK_STRUCT_PENDING_BIT was already set. > So in effect your second call to queue_work will just return. Best thing to do is just disable interrupt as soon as you receive first interrupt and re-enable it when you think you can handle it.I hope you are not writing network driver where this sequence would cause unacceptable delays. > > HTH > > Thanks, > Arun > > >> >> Questions: >> >> 1) Is it possible that the instance that was queued by 2nd interrupt, can get to run BEFORE the instance that was queued by 1st interrupt? In other words, is reordering possible? >> >> 2) Is it possible that one running instance of the function, can get preempted by second instance of the same work queue? I read through http://lwn.net/Articles/511421/ and it talks about same work queue cannot run on different CPU, but I have doubt about single CPU. If If I am writing a worker function, does my code have to be ready that it can be preempted by another instance of the same function? >> >> Please note that I understand that my worker function can preempted by other processes, my doubts are related to the same workqueue. >> >> Thanks, >> >> Rajat >> >> >> _______________________________________________ >> Kernelnewbies mailing list >> [email protected] >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > _______________________________________________ > Kernelnewbies mailing list > [email protected] > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs