> > Subject: RE: [PATCH 1/1] net/mana: add 32 bit short doorbell > > > > > > > +#ifdef RTE_ARCH_32 > > > > > + uint16_t cqe_incr = > > > > > +(uint16_t)rxq->gdma_cq.head_incr_to_short_db; > > > > > > > > How do you make sure head_incr_to_short_db doesn't overflow? > > > > > > > > > > I have checked this with hardware team. In my opinion it would be > > > easily overflown. > > > The hw team seems suggesting the hw will take care of this. > > > > > > Thanks, > > > Wei > > > > I'm not sure how HW can take care of this when it overflows. When it > > happens, the HW will miss a doorbell and CQ queue will get full. And > > eventually you'll lose completions for TX/RX. > > > > In mana_alloc_and_post_rx_wqes() and mana_rx_burst(), the code has > > check for RX/TX_WQE_SHORT_DB_THRESHOLD to make sure tail_incr doesn't > > overflow when ringing the doorbell. > > > > In gdma_poll_completion_queue(), you need to have a similar mechanism > > to not overflow tail_incr when ringing the doorbell. > > > I am not sure what can be done here. Applications could run in poll mode > without > need to ring cq doorbell, or it could take very long time before it change the > interrupt state. What we can do when cq->head_incr_to_short_db reaches 0xffff > in gdma_poll_completion_queue()? > > If it breaks out the loop and return, the next time it enters it may still > at0xffff > because it has not rung doorbell the have it reset yet. > > If just resetting the value to 0 and let it keep going in the loop, it is no > difference > than casting it to 16 bit unsigned int, which would be done in > mana_arm_cq() if it is eventually called. > > Anyway, ringing cq doorbell has not been tested as the driver doesn't support > interrupts.
If 32bit doorbell doesn't support interrupts, you can remove this feature from 32 bits. Long
