Ordering / preemption of work in a workqueue preempt?

[anish singh]

On Fri, Nov 15, 2013 at 5:01 PM, Rajat Sharma <fs.rajat at gmail.com> wrote:
> Hi Rajat,
>
>
> On Fri, Nov 15, 2013 at 7:16 AM, Rajat Jain <rajatjain at juniper.net> 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.
>>
>> 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?
use alloc_ordered_workqueue: only one workqueue will be active at a time
and it will execute in the queued sequence.
>
>
> It is unlikely as workqueue would have internal queing of tasks.
>
>>
>>
>> 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?
>>
>
> Do you mean the system has just one CPU, then there would be just one worker
> thread in the workqueue which will pick up requests one by one. Do you see
> multiple threads?
>
>>
>> Please note that I understand that my worker function can preempted by
>> other processes, my doubts are related to the same workqueue.
>>
>> Thanks,
>>
>> Rajat
>>
>>
>
> Rajat
>
>>
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