On 17/06/2020 20:49, Gal Pressman wrote: > On 17/06/2020 18:36, Jason Gunthorpe wrote: >> On Tue, Jun 16, 2020 at 08:44:37PM +0300, Gal Pressman wrote: >>> On 16/06/2020 12:38, Leon Romanovsky wrote: >>>> On Tue, Jun 16, 2020 at 11:53:11AM +0300, Gal Pressman wrote: >>>>> On 16/06/2020 9:30, Leon Romanovsky wrote: >>>>>> On Mon, Jun 15, 2020 at 10:59:20AM +0300, Gal Pressman wrote: >>>>>>> Provider specific attributes which are necessary for the userspace >>>>>>> functionality should be part of the alloc ucontext response, not query >>>>>>> device. This way a userspace provider could work without issuing a query >>>>>>> device verb call. However, the fields will remain in the query device >>>>>>> ABI in order to maintain backwards compatibility. >>>>>> >>>>>> I don't really understand why "should be ..."? Device properties exposed >>>>>> here are per-device and will be equal to all ucontexts, so instead of >>>>>> doing one very fast system call, you are "punishing" every ucontext >>>>>> call. >>>>> >>>>> I talked about it with Jason in the past, the query device verb is intended to >>>>> follow the IBA verb, alloc ucontext should return driver specific data that's >>>>> required to operate the user space provider. >>>>> A query device call should not be mandatory to load the provider. >>>> >>>> Why? query_device is declared as mandatory verb for any provider, so >>>> anyway all in-the-tree RDMA drivers will have such verb. >>> >>> I don't think the concern here is if the verb exists or not, my understanding is >>> that query device should be used for IBA query device attributes, not other >>> provider specific stuff. >>> Jason, want to chime in with your thoughts? >> >> query_device should be used to implement the ibverb query_device and >> query_device_ex >> >> It should only return rdma-core defined common stuff because that is >> what that verb does - there is no reason to return driver specific >> things as there is nothing the driver can do with it. >> >> The only exception might be some provider specific query_device dv >> that needs more information. >> >> query_device should not be used as some two-part >> create_context. Information related only to create_context that is not >> already exposed to query_device should not be added to query_device >> only for create_context's use. >> >> Similarly, information in query_device should not be duplicated into >> create_context just to save a system call. > > That makes sense. > To clarify, the "duplicated" fields in this patch are moved to the ucontext > allocation, where they originally belong as all of them are necessary for the > provider's functionality. > Future fields such as these will only be added to alloc_ucontext, not both, so > there's no duplication. > > Otherwise, future extensions will either have to be added to query_device, which > is the wrong place, just to be consistent with the existing code. Or we add them > to the ucontext response, where they belong, and end up with some hybrid > solution where different fields are gathered from different places (yuck :\). > > We got it wrong the first place but it's a two way door, let's fix it. Uhh.. We can't really get rid of the query device call as the provider needs the max_qp attribute in order to allocate the QP table properly. I still think we should move the fields to keep things clean, but I can drop this change if you prefer to avoid the churn. The provider will always call query device on context initialization and gather different fields from different system calls. Thoughts?
