Re: [PATCH 0/2] io_uring: add a CQ ring flag to enable/disable eventfd notification

[Stefano Garzarella <sgarzare@redhat.com>]

On Fri, May 15, 2020 at 08:24:58AM -0600, Jens Axboe wrote:
> On 5/15/20 4:54 AM, Stefano Garzarella wrote:
> > The first patch adds the new 'cq_flags' field for the CQ ring. It
> > should be written by the application and read by the kernel.
> > 
> > The second patch adds a new IORING_CQ_NEED_WAKEUP flag that can be
> > used by the application to enable/disable eventfd notifications.
> > 
> > I'm not sure the name is the best one, an alternative could be
> > IORING_CQ_NEED_EVENT.
> > 
> > This feature can be useful if the application are using eventfd to be
> > notified when requests are completed, but they don't want a notification
> > for every request.
> > Of course the application can already remove the eventfd from the event
> > loop, but as soon as it adds the eventfd again, it will be notified,
> > even if it has already handled all the completed requests.
> > 
> > The most important use case is when the registered eventfd is used to
> > notify a KVM guest through irqfd and we want a mechanism to
> > enable/disable interrupts.
> > 
> > I also extended liburing API and added a test case here:
> > https://github.com/stefano-garzarella/liburing/tree/eventfd-disable
> 
> Don't mind the feature, and I think the patches look fine. But the name
> is really horrible, I'd have no idea what that flag does without looking
> at the code or a man page. Why not call it IORING_CQ_EVENTFD_ENABLED or
> something like that? Or maybe IORING_CQ_EVENTFD_DISABLED, and then you
> don't have to muck with the default value either. The app would set the
> flag to disable eventfd, temporarily, and clear it again when it wants
> notifications again.

You're clearly right! :-) The name was horrible.

I agree that IORING_CQ_EVENTFD_DISABLED should be the best.
I'll send a v2 changing the name and removing the default value.

Thanks,
Stefano