On Mon, 14 Sep 2026 13:58:08 +0300
Rita Ruvinsky <[email protected]> wrote:
> gdma_post_work_request() subtracted a unit count from an entry count:
>
> queue_free_units = queue->count - (queue->head - queue->tail);
>
> queue->count is in entries, while head and tail are in WQE alignment
> units. On a 512-entry, 128KB send queue the check saw 512 units of
> capacity instead of queue->size / GDMA_WQE_ALIGNMENT_UNIT_SIZE = 4096,
> and returned -EBUSY with the queue one eighth full. A workload that
> fills that window faster than it drains makes rte_eth_tx_burst() return
> 0 for long enough to look like a dead port.
>
> Derive the capacity from queue->size, which is also what the ring wrap
> in gdma_get_wqe_pointer() uses. Rx is unaffected: its WQEs occupy
> exactly one unit, so entries and units coincide.
>
> Fixes: 56dd45c0ce7b ("net/mana: implement hardware layer operations")
> Cc: [email protected]
>
> Signed-off-by: Rita Ruvinsky <[email protected]>
> ---
Applied to next-net
The long form AI review had some observations worth including:
On Mon, 14 Sep 2026 13:58:08 +0300
Rita Ruvinsky <[email protected]> wrote:
> gdma_post_work_request() subtracted a unit count from an entry count:
The unit analysis is right. head/tail are advanced in alignment
units (queue->head += wqe_size / GDMA_WQE_ALIGNMENT_UNIT_SIZE, and
gdma_get_wqe_pointer() multiplies head by the same constant), while
sq_count comes from rdma-core as attr->cap.max_send_wr and sq_size as
align_hw_size(max_send_wr * get_wqe_size(max_send_sge)). Deriving the
capacity from size is the only self-consistent choice, and it is what
mana_gd_wq_avail_space() in the kernel driver does.
Info:
1. The debug line in the -EBUSY path still reports queue->count:
DP_LOG(DEBUG, "WQE size %u queue count %u head %u tail %u",
wqe_size, queue->count, queue->head, queue->tail);
After this patch count no longer takes part in the decision for the
send or receive queue; only gdma_poll_completion_queue() still uses it,
for the CQ. The one line printed when a post is rejected no longer
shows what it was rejected against. Suggest:
DP_LOG(DEBUG, "WQE size %u queue size %u free %u head %u tail %u",
wqe_size, queue->size, queue_free_units,
queue->head, queue->tail);
2. The comment describes the old bug rather than the invariant:
/* head/tail count WQE alignment units, so the capacity they are
* compared against must too: queue->count is in entries and
* undercounts the queue, stalling Tx well below capacity.
*/
The stall belongs in the commit message, where it already is. In the
source the invariant is enough:
/* head and tail are in WQE alignment units, so the capacity must
* come from the queue size in bytes, not the entry count.
*/
3. Worth a sentence in the commit message that the kernel mana driver
computes the same limit in mana_gd_wq_avail_space(), in bytes:
u32 used_space = (wq->head - wq->tail) * GDMA_WQE_BU_SIZE;
return wq->queue_size - used_space;
It is independent confirmation of the unit convention and tells anyone
backporting this that the two drivers now agree.
