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

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Date:   Fri, 15 May 2020 09:13:33 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 0/2] io_uring: add a CQ ring flag to enable/disable
 eventfd notification

On 5/15/20 8:34 AM, Stefano Garzarella wrote:
> 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.

Sometimes you go down that path on naming and just can't think of
the right one. I think we've all been there.

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

Great thanks, and please do queue a pull for the liburing side too.

-- 
Jens Axboe