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

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Message-ID: <20250126103952.00005556@gmail.com>
Date: Sun, 26 Jan 2025 10:39:52 +0800
From: Furong Xu <0x1207@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Ido Schimmel <idosch@...sch.org>, Brad Griffis <bgriffis@...dia.com>,
 Jon Hunter <jonathanh@...dia.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Alexander Lobakin <aleksander.lobakin@...el.com>, Joe Damato
 <jdamato@...tly.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Maxime
 Coquelin <mcoquelin.stm32@...il.com>, xfr@...look.com,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH net-next v3 1/4] net: stmmac: Switch to zero-copy in
 non-XDP RX path

On Sat, 25 Jan 2025 20:08:12 +0100, Andrew Lunn <andrew@...n.ch> 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@gmail.com/

> Are there other use cases where SPH is needed?

https://patchwork.kernel.org/project/netdevbpf/cover/20240910171458.219195-1-almasrymina@google.com/
https://patchwork.kernel.org/project/netdevbpf/cover/20250116231704.2402455-1-dw@davidwei.uk/

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