Hi,
I'm looking for clarification of the behavior of queue_work(). From
the header description, I'm not sure if I need additional complexity
for re-queuing work.
I want to ensure the following cases all occur when calling queue_work().
1) work_struct not queued -> work_struct queued
2) work_struct queued -> work_struct queued (no change)
3) work_struct running -> work_struct queued (so it will run again)
1 & 2 look supported from workqueue.h. Is the 3rd case true and
guaranteed? Is it okay to re-use the same work_struct in that case
while it's being executed? A work_struct function can re-queue
itself, so I hope #3 is supported.
The virtual device I'm working on has a single interrupt shared for
multiple rings. So whenever an interrupt occurs, I need to re-queue
the single work_struct on the workqueue to ensure we don't miss an
event. That is, we need to re-iterate all the rings if the interrupt
comes halfway through processing the list of rings. If multiple
interrupts come through while running, we only need to re-queue a
single work item for all of them.
Below is what I hope works for the code to give something tangible.
Thank you,
Jason
DECLARE_WORK(argo_work, argo_work_fn);
static struct workqueue_struct *argo_wq = alloc_workqueue("argo_wq",
WQ_UNBOUND | WQ_HIGHPRI | WQ_CPU_INTENSIVE | WQ_SYSFS, 1);
static void argo_work_fn(struct work_struct *work)
{
argo_interrupt_rx(); /* iterates multiple "rings" */
argo_notify();
}
static irqreturn_t argo_interrupt(int irq, void *dev_id)
{
queue_work(argo_wq, &argo_work);
return IRQ_HANDLED;
}
Hello, Jason.
On Thu, May 20, 2021 at 08:39:56AM -0400, Jason Andryuk wrote:
> 1 & 2 look supported from workqueue.h. Is the 3rd case true and
> guaranteed? Is it okay to re-use the same work_struct in that case
Yes.
> while it's being executed? A work_struct function can re-queue
Yes.
> itself, so I hope #3 is supported.
Yes.
> DECLARE_WORK(argo_work, argo_work_fn);
> static struct workqueue_struct *argo_wq = alloc_workqueue("argo_wq",
> WQ_UNBOUND | WQ_HIGHPRI | WQ_CPU_INTENSIVE | WQ_SYSFS, 1);
I don't know what the device is but does it need both HIGHPRI and
CPU_INTENSIVE?
> static void argo_work_fn(struct work_struct *work)
> {
> argo_interrupt_rx(); /* iterates multiple "rings" */
> argo_notify();
> }
>
> static irqreturn_t argo_interrupt(int irq, void *dev_id)
> {
> queue_work(argo_wq, &argo_work);
>
> return IRQ_HANDLED;
> }
Yeah, the above will guarantee that the work function would run at least
once since the last invocation of argo_interrupt().
Thanks.
--
tejun
Hello, Tejun.
On Thu, May 20, 2021 at 1:01 PM Tejun Heo <[email protected]> wrote:
>
> Hello, Jason.
>
> On Thu, May 20, 2021 at 08:39:56AM -0400, Jason Andryuk wrote:
> > 1 & 2 look supported from workqueue.h. Is the 3rd case true and
> > guaranteed? Is it okay to re-use the same work_struct in that case
>
> Yes.
>
> > while it's being executed? A work_struct function can re-queue
>
> Yes.
>
> > itself, so I hope #3 is supported.
>
> Yes.
>
> > DECLARE_WORK(argo_work, argo_work_fn);
> > static struct workqueue_struct *argo_wq = alloc_workqueue("argo_wq",
> > WQ_UNBOUND | WQ_HIGHPRI | WQ_CPU_INTENSIVE | WQ_SYSFS, 1);
>
> I don't know what the device is but does it need both HIGHPRI and
> CPU_INTENSIVE?
argo is a Xen inter-vm communication mechanism, so networking-ish. I
wanted HIGHPRI to ensure it is run promptly. I wasn't sure about
CPU_INTENSIVE, but high data rates could potentially copy a fair
amount of data. HIGHPRI alone may be sufficient.
> > static void argo_work_fn(struct work_struct *work)
> > {
> > argo_interrupt_rx(); /* iterates multiple "rings" */
> > argo_notify();
> > }
> >
> > static irqreturn_t argo_interrupt(int irq, void *dev_id)
> > {
> > queue_work(argo_wq, &argo_work);
> >
> > return IRQ_HANDLED;
> > }
>
> Yeah, the above will guarantee that the work function would run at least
> once since the last invocation of argo_interrupt().
Awesome. Thank you, Tejun.
Regards,
Jason