Re: [PATCH net-next v3 1/4] net: stmmac: Switch to zero-copy in non-XDP RX path

[Furong Xu]

On Sat, 25 Jan 2025 20:08:12 +0100, Andrew Lunn <andrew@xxxxxxx> wrote:

> > It is recommended to disable the "SPH feature" by default unless
> > some certain cases depend on it. Like Ido said, two large buffers
> > being allocated from the same page pool for each packet, this is a
> > huge waste of memory, and brings performance drops for most of
> > general cases.  
> 
> I don't know this driver, but it looks like SPH is required for
> NETIF_F_GRO? Can you add this flag to hw_features, but not
> wanted_features and leave SPH disabled until ethtool is used to enable
> GRO?

SPH has its own ethtool command, stmmac driver does not implement yet.
see:
https://patchwork.kernel.org/project/netdevbpf/cover/20250114142852.3364986-1-ap420073@xxxxxxxxx/

> Are there other use cases where SPH is needed?

https://patchwork.kernel.org/project/netdevbpf/cover/20240910171458.219195-1-almasrymina@xxxxxxxxxx/
https://patchwork.kernel.org/project/netdevbpf/cover/20250116231704.2402455-1-dw@xxxxxxxxxxx/

The stmmac driver does not support both of them, but it will someday :)