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From: Jiufei Xue <[email protected]>
To: Jens Axboe <[email protected]>
Cc: [email protected]
Subject: Re: [PATCH liburing 1/2] io_uring_enter: add timeout support
Date: Fri, 31 Jul 2020 10:12:59 +0800	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>



On 2020/7/30 下午11:28, Jens Axboe wrote:
> On 7/29/20 8:32 PM, Jiufei Xue wrote:
>> Hi Jens,
>>
>> On 2020/7/30 上午1:51, Jens Axboe wrote:
>>> On 7/29/20 4:10 AM, Jiufei Xue wrote:
>>>> Kernel can handle timeout when feature IORING_FEAT_GETEVENTS_TIMEOUT
>>>> supported. Add two new interfaces: io_uring_wait_cqes2(),
>>>> io_uring_wait_cqe_timeout2() for applications to use this feature.
>>>
>>> Why add new new interfaces, when the old ones already pass in the
>>> timeout? Surely they could just use this new feature, instead of the
>>> internal timeout, if it's available?
>>>
>> Applications use the old one may not call io_uring_submit() because
>> io_uring_wait_cqes() will do it. So I considered to add a new one.
> 
> Not sure I see how that's a problem - previously, you could not do that
> either, if you were doing separate submit/complete threads. So this
> doesn't really add any new restrictions. The app can check for the
> feature flag to see if it's safe to do so now.
>Yes, new applications can check for the feature flag. What about the existing
apps? The existing applications which do not separate submit/complete
threads may use io_uring_wait_cqes() or io_uring_wait_cqe_timeout() without
submiting the requests. No one will do that now when the feature is supported.


>>>> diff --git a/src/include/liburing.h b/src/include/liburing.h
>>>> index 0505a4f..6176a63 100644
>>>> --- a/src/include/liburing.h
>>>> +++ b/src/include/liburing.h
>>>> @@ -56,6 +56,7 @@ struct io_uring {
>>>>  	struct io_uring_sq sq;
>>>>  	struct io_uring_cq cq;
>>>>  	unsigned flags;
>>>> +	unsigned features;
>>>>  	int ring_fd;
>>>>  };
>>>
>>> This breaks the API, as it changes the size of the ring...
>>>
>> Oh, yes, I haven't considering that before. So could I add this feature
>> bit to io_uring.flags. Any suggestion?
> 
> Either that, or we add this (and add pad that we can use later) and just
> say that for the next release you have to re-compile against the lib.
> That will break existing applications, unless they are recompiled... But
> it might not be a bad idea to do so, just so we can pad io_uring out a
> little bit to provide for future flexibility.
>
Agree about that. So should we increase the major version after adding the
feature flag and some pad?

Thanks,
Jiufei

  reply	other threads:[~2020-07-31  2:13 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-29 10:10 [PATCH liburing 0/2] add two interfaces for new timeout feature Jiufei Xue
2020-07-29 10:10 ` [PATCH liburing 1/2] io_uring_enter: add timeout support Jiufei Xue
2020-07-29 17:51   ` Jens Axboe
2020-07-30  2:32     ` Jiufei Xue
2020-07-30 15:28       ` Jens Axboe
2020-07-31  2:12         ` Jiufei Xue [this message]
2020-07-31  2:56           ` Jens Axboe
2020-07-31  3:16             ` Jiufei Xue
2020-07-31  3:57               ` Jens Axboe
2020-08-03  3:16                 ` Jiufei Xue
2020-08-03 16:41                   ` Jens Axboe
2020-08-03 19:16                     ` Stefan Metzmacher
2020-08-04  1:29                     ` Jiufei Xue
2020-08-04  4:50                       ` Jens Axboe
2020-08-04  5:04                         ` Jiufei Xue
2020-08-04  5:19                           ` Jens Axboe
2020-07-29 10:10 ` [PATCH liburing 2/2] test/timeout: add testcase for new timeout interface Jiufei Xue

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