RE: [EXTERNAL] Re: [PATCH net-next v2] net: mana: Set default number of queues to 16

[Long Li]

> On Mon, 23 Mar 2026 12:49:25 -0700 Long Li wrote:
> > Set the default number of queues per vPort to MANA_DEF_NUM_QUEUES
> > (16), as 16 queues can achieve optimal throughput for typical
> > workloads. The actual number of queues may be lower if it exceeds the
> > hardware reported limit. Users can increase the number of queues up to
> > max_queues via ethtool if needed.
> 
> Sorry we are a bit backlogged I didn't spot this in time (read: I'm planning to
> revert this unless proper explanation is provided)
> 
> Could you explain why not use netif_get_num_default_rss_queues() ?
> Having local driver innovations is a major PITA for users who deal with
> heterogeneous envs.

  Hi Jakub,

  We considered netif_get_num_default_rss_queues() but chose a fixed default based on our performance testing. On Azure VMs, typical
  workloads plateau at around 16 queues - adding more queues beyond that doesn't improve throughput but increases memory usage and
  interrupt overhead.

  netif_get_num_default_rss_queues() would return 32-64 on large VMs (64-128 vCPUs), which wastes resources without benefit.

  That said, I agree that completely ignoring the core-based heuristic isn't ideal for consistency. One option is to use
  netif_get_num_default_rss_queues() but clamp it to a maximum of MANA_DEF_NUM_QUEUES (16), so small VMs still get enough queues and
  large VMs don't over-allocate. Something like:

   apc->num_queues = min(netif_get_num_default_rss_queues(), MANA_DEF_NUM_QUEUES);
   apc->num_queues = min(apc->num_queues, gc->max_num_queues);

  For reference, it seems mlx4 does something similar - it caps at DEF_RX_RINGS (16) regardless of core count.

  Do you want me to send a v2?

  Thanks, 
  Long