> On 31 Mar 2021, at 15:15, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > > On Wed, Mar 31, 2021 at 12:58:41PM +0000, Haakon Bugge wrote: >> >> >>> On 31 Mar 2021, at 14:00, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: >>> >>> On Wed, Mar 31, 2021 at 10:38:02AM +0000, Haakon Bugge wrote: >>>> >>>> >>>>> On 31 Mar 2021, at 01:12, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: >>>>> >>>>> On Thu, Mar 25, 2021 at 02:05:47PM +0100, Håkon Bugge wrote: >>>>>> Introduce the ability for both user-space and kernel ULPs to adjust >>>>>> the minimum RNR Retry timer. The INIT -> RTR transition executed by >>>>>> RDMA CM will be used for this adjustment. This avoids an additional >>>>>> ib_modify_qp() call. >>>>> >>>>> Can't userspace override the ibv_modify_qp() call the librdmacm wants >>>>> to make to do this? >>>> >>>> Not sure I understand. The point is, that user-land which intends to >>>> set said timer, can do so without an additional ibv_modify_qp() >>>> call. May be I should have added: >>> >>> IIRC in userspace the application has the option to call >>> ibv_modify_qp() so it can just change it before it makes the call? >> >> User-space can call ibv_modify_qp, but that call is inherently >> expensive on some HCA implementations running virtualized. > > you are not following. > > In rdmacm userspace *always* calls the ibv_modify_qp > > rdmacm has a 'helper' mode where it hides the call inside its logic in > librdmacm. > > But, IIRC, a ULP can get some event and do the ibv_modify_qp in its > logic instead of using the hidden version inside rdma cm. Though that > may only be possible if you eliminate the entire librdmacm hidden logic > > It just seems wrong to send data to the kernel just to have the kernel > copy that same data out to another system call and never use it at > all. > > Actually I bet you could do this same thing entirely in userspace by > adjusting rdma_init_qp_attr() to copy the data that would be stored in > the cm_id.. ?? This will definitely not solve the issue for kernel ULP, e.g., RDS. Further, why do we have rdma_set_option() with option RDMA_OPTION_ID_ACK_TIMEOUT ? Let me dig into what you're saying. Thxs, Håkon > > Jason
