Re: [PATCH 3/3] migration/rdma: Retry control sends on full queue

[Peter Xu <peterx@redhat.com>]

On Mon, Aug 17, 2026 at 06:51:17PM +0800, Yanfei Xu wrote:
> RAM writes and control messages share the send queue.  If
> outstanding writes fill it, RDMA writes drain a completion and retry,
> but control sends fail the migration.
> 
> Drain one outstanding write and retry the control send on ENOMEM.
> 
> Signed-off-by: Yanfei Xu <yanfei.xu@bytedance.com>
> ---
>  migration/rdma.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/rdma.c b/migration/rdma.c
> index 6e8436ccc1..d1f44a5f55 100644
> --- a/migration/rdma.c
> +++ b/migration/rdma.c
> @@ -1572,9 +1572,19 @@ static int qemu_rdma_post_send_control(RDMAContext *rdma, uint8_t *buf,
>          memcpy(wr->control + sizeof(RDMAControlHeader), buf, head->len);
>      }
>  
> -
> +retry:
>      ret = ibv_post_send(rdma->qp, &send_wr, &bad_wr);
>  
> +    if (ret == ENOMEM && rdma->nb_sent) {
> +        ret = qemu_rdma_block_for_wrid(rdma, RDMA_WRID_RDMA_WRITE, NULL);
> +        if (ret < 0) {
> +            error_setg(errp, "rdma migration: failed to make room for "
> +                       "control send");
> +            return -1;
> +        }
> +        goto retry;
> +    }

Looks also correct, but two questions:

- Should we provide a helper instead of duplicating the WRITE op handling?
  I believe only WRITE wrids can be on the fly.

- Could ENOMEM be returned when nb_sent==0?  If that check applies to WRITE
  path too?

Thanks,

> +
>      if (ret > 0) {
>          error_setg(errp, "Failed to use post IB SEND for control");
>          return -1;
> -- 
> 2.20.1
> 

-- 
Peter Xu