On Tue, May 20, 2025, Peter Zijlstra wrote:
> On Mon, May 19, 2025 at 11:55:10AM -0700, Sean Christopherson wrote:
> > Drop the setting of WQ_FLAG_EXCLUSIVE from add_wait_queue_priority() to
> > differentiate it from add_wait_queue_priority_exclusive(). The one and
> > only user add_wait_queue_priority(), Xen privcmd's irqfd_wakeup(),
> > unconditionally returns '0', i.e. doesn't actually operate in exclusive
> > mode.
>
> I find:
>
> drivers/hv/mshv_eventfd.c: add_wait_queue_priority(wqh, &irqfd->irqfd_wait);
> drivers/xen/privcmd.c: add_wait_queue_priority(wqh, &kirqfd->wait);
>
> I mean, it might still be true and all, but hyperv seems to also use
> this now.
Oh FFS, another "heavily inspired by KVM". I should have bribed someone to take
this series when I had the chance. *sigh*
Unfortunately, the Hyper-V code does actually operate in exclusive mode. Unless
you have a better idea, I'll tweak the series to:
1. Drop WQ_FLAG_EXCLUSIVE from add_wait_queue_priority() and have the callers
explicitly set the flag,
2. Add a patch to drop WQ_FLAG_EXCLUSIVE from Xen privcmd entirely.
3. Introduce add_wait_queue_priority_exclusive() and switch KVM to use it.
That has an added bonus of introducing the Xen change in a dedicated patch, i.e.
is probably a sequence anyways.
Alternatively, I could rewrite the Hyper-V code a la the KVM changes, but I'm not
feeling very charitable at the moment (the complete lack of documentation for
their ioctl doesn't help).
