Re: [Intel-wired-lan] [PATCH iwl-next 0/3] iavf: defer loading netmem_desc

From: Matt Vollrath <[email protected]>
Date: Fri, 31 Jul 2026 08:41:06 -0400

> In a few places libeth and the iavf driver inspect which page pool is
> attached to a netmem_ref. This forces an immediate load of the
> netmem_desc struct for each buffer in the Rx loop.
> 
> Defer or eliminate these loads of netmem_desc from the driver fast path
> by using the page_pool ref in the first cache line of iavf_ring instead.

I was thinking of this when implementing the current design, but:

Do you have any data to prove this actually helps performance?

> 
> There are only two paths out of the Rx loop where netmem_desc needs to
> be consumed:
> * The "very rare" case of libeth_rx_sync_for_cpu calling
>   libeth_rx_recycle_slow and indicating that there was no data. This
>   could be similarly factored out, but not by this series.
> * GRO merging a frame into an existing aggregate stream. In this case,
>   the cold load of netmem_desc may overlap the payload prefetch started
>   by iavf_build_skb, which is now no longer dependent on netmem_desc to
>   start.

Thanks,
Olek