On 2020/7/31 上午10:56, Jens Axboe wrote: > On 7/30/20 8:12 PM, Jiufei Xue wrote: >> >> >> 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. > > Right, and I feel like I'm missing something here, what's the issue with > that? As far as the application is concerned, a different mechanism may be > used to achieve the timeout, but it should work in the same way. > > So please explain this as clearly as you can, as I'm probably missing > something... > I am sorry for the confusion. Here is an example below: io_uring_get_sqe io_uring_prep_nop io_uring_wait_cqe_timeout If an existing application call io_uring_wait_cqe_timeout() after preparing some sqes, the older APIs will submit the requests. However, If we reuse the existing APIs and found the feature is supported, we will not submit the requests. I think we should not change the behaviors for existing APIs. Thanks, Jiufei >>>> 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? > > I think so, also a good time to think about other cases where that might be > useful. > > But I think we need to flesh out the API first, as that might impact things. >
