On Wed, Mar 18, 2020 at 02:36:35PM +0200, Yishai Hadas wrote: > On 3/18/2020 1:43 PM, Jason Gunthorpe wrote: > > On Wed, Mar 18, 2020 at 09:52:27AM +0200, Yishai Hadas wrote: > > > > > We can really consider extending the functionality of a parent domain that > > > was just added for CQ in case it holds a thread domain for this purpose. > > > However, current code enforces creating a dedicated BF as part of thread > > > domain unless we extend ibv_alloc_td() to ask only for marking the single > > > thread functionality. > > > > Doesn't the CQ need a BF too? > > Not really, it uses a per-allocated device one for writing 8 bytes for > doorbell, applicable only in the arm/events mode. But this also wastes a BF, if the app is only running a single lockless TD then the CQ could use the BF from the TD, shared with the QP and not allocate another one > > > The existing alternative is or to use the legacy ENV that mentioned above or > > > to use the ibv_cq_ex functionality which upon its creation gets an explicit > > > flag for single threaded one (i.e. IBV_CREATE_CQ_ATTR_SINGLE_THREADED). > > > > An apps that don't want the BF can always use > > IBV_CREATE_CQ_ATTR_SINGLE_THREADED > > > > This requires moving to the new polling mechanism where this option is > really applicable (see a3a31e8dc6a3fbf577dd8b12742d0c70cf63bd29). cq_ex is pollable the normal way if converted with ibv_cq_ex_to_cq() It is also a bug if the old env driven lock elimination doesn't trigger for normal CQ poll if IBV_CREATE_CQ_ATTR_SINGLE_THREADED is specified. Jason
