[v2,0/2] io_uring: add a CQ ring flag to enable/disable eventfd notification

Message

Stefano Garzarella May 15, 2020, 4:38 p.m. UTC

v1 -> v2:
 - changed the flag name and behaviour from IORING_CQ_NEED_EVENT to
   IORING_CQ_EVENTFD_DISABLED [Jens]

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_EVENTFD_DISABLED flag that can be
used by the application to disable/enable eventfd notifications.

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

Stefano Garzarella (2):
  io_uring: add 'cq_flags' field for the CQ ring
  io_uring: add IORING_CQ_EVENTFD_DISABLED to the CQ ring flags

 fs/io_uring.c                 | 12 +++++++++++-
 include/uapi/linux/io_uring.h | 11 ++++++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)

Comments

Jens Axboe May 15, 2020, 6:17 p.m. UTC | #1

On 5/15/20 10:38 AM, Stefano Garzarella wrote:
> v1 -> v2:
>  - changed the flag name and behaviour from IORING_CQ_NEED_EVENT to
>    IORING_CQ_EVENTFD_DISABLED [Jens]
> 
> 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_EVENTFD_DISABLED flag that can be
> used by the application to disable/enable eventfd notifications.
> 
> 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.

Thanks, applied.