[PATCH] net/i40e: Fast release optimizations

[Morten Brørup]

> From: Morten Brørup [mailto:mb at smartsharesystems.com]
> Sent: Tuesday, 24 June 2025 08.13
> 
> When fast releasing mbufs, the mbufs are not accessed, so do not prefetch
> them.
> This saves a mbuf load operation for each fast released TX mbuf.
> 
> When fast release of mbufs is enabled for a TX queue, cache the mbuf
> mempool pointer in the TX queue structure.
> This saves one mbuf load operation for each burst of fast released TX
> mbufs.
> 
> The txep->mbuf pointer is not used after the mbuf has been freed, so do
> not reset the pointer.
> This saves a txep store operation for each TX mbuf freed.
> 
> Signed-off-by: Morten Brørup <mb at smartsharesystems.com>
> ---

After further consideration, I think this patch should be split in two:
1. Remove superfluous code: prefetching mbufs and resetting txep->mbuf pointers.
2. Cache the mbuf mempool pointer for FAST_FREE.

-Morten