> Subject: RE: [PATCH net] net: mana: Fix doorbell out of order violation and avoid
> unnecessary doorbell rings
>
> > From: longli@xxxxxxxxxxxxxxxxx <longli@xxxxxxxxxxxxxxxxx>
> > Sent: Monday, August 5, 2024 4:38 PM
> > [...]
> > After napi_complete_done() is called, another NAPI may be running on
> > another CPU and ring the doorbell before the current CPU does. When
>
> Can you please share more details about "another NAPI"? Is it about busy_poll?
>
> > combined with unnecessary rings when there is no need to ARM the CQ,
> > this triggers error paths in the hardware.
> >
> > Fix this by always ring the doorbell in sequence and avoid unnecessary
> > rings.
>
> I'm not sure what "error paths in the hardware" means. It's better to describe the
> user-visible consequence.
>
> Maybe this is clearer:
>
> When there is no need to arm the CQ from NAPI's perspective, the driver must
> not combine "too many" arming operations due to a MANA hardware
> requirement:
> the driver must ring the doorbell at least once within every 8 wraparounds of the
> CQ, otherwise "XXX" would happen. //Dexuan: I don't know what the "XXX" is
>
> Add a per-CQ counter cq->work_done_since_doorbell, and make sure the CQ is
> armed within 4 wraparounds of the CQ. //Dexuan: why not 8 or 7?
I'm sending v2 to address the details in the comments.
>
>
> > + if (w < cq->budget) {
> > + mana_gd_ring_cq(gdma_queue, SET_ARM_BIT);
> > + cq->work_done_since_doorbell = 0;
> > + napi_complete_done(&cq->napi, w);
> > + } else if (cq->work_done_since_doorbell >
> > + cq->gdma_cq->queue_size / COMP_ENTRY_SIZE * 4) {
> > + /* MANA hardware requires at least one doorbell ring every 8
> s/ring every 8/arming within every 8/ ?
>
> > + * wraparounds of CQ even there is no need to ARM. This
> > driver
>
> s/ARM/arming/ ?
> s/even/even if/ ?
Will fix this in v2.
Thanks,
Long
