From: Guillaume Nault <gna...@redhat.com>
Date: Fri, 2 Aug 2019 17:15:03 +0200
> Before commit d4289fcc9b16 ("net: IP6 defrag: use rbtrees for IPv6
> defrag"), a netperf UDP_STREAM test[0] using big IPv6 datagrams (thus
> generating many fragments) and running over an IPsec tunnel, reported
> more than 6Gbps throughput. After that patch, the same test gets only
> 9Mbps when receiving on a be2net nic (driver can make a big difference
> here, for example, ixgbe doesn't seem to be affected).
>
> By reusing the IPv4 defragmentation code, IPv6 lost fragment coalescing
> (IPv4 fragment coalescing was dropped by commit 14fe22e33462 ("Revert
> "ipv4: use skb coalescing in defragmentation"")).
...
> Re-introducing fragment coalescing is enough to get the initial
> performances again (6.6Gbps with be2net): driver doesn't drop frames
> anymore (no more rx_drops_no_frags errors) and the reassembly engine
> works at full speed.
>
> This patch is quite conservative and only coalesces skbs for local
> IPv4 and IPv6 delivery (in order to avoid changing skb geometry when
> forwarding). Coalescing could be extended in the future if need be, as
> more scenarios would probably benefit from it.
Eric and Florian, please review.
