linux-kernel - Re: [PATCH net-next 3/5] netdev_features: convert NETIF_F

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Message-ID: <CANn89iK-=36NV2xmTqY3Zge1+oHnrOfTXGY0yrH=jiRWvKAzkg@mail.gmail.com>
Date: Tue, 25 Jun 2024 16:00:51 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Andrew Lunn <andrew@...n.ch>, 
	nex.sw.ncis.osdt.itp.upstreaming@...el.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 3/5] netdev_features: convert NETIF_F_LLTX to dev->lltx

On Tue, Jun 25, 2024 at 1:50 PM Alexander Lobakin
<aleksander.lobakin@...el.com> wrote:
>
> NETIF_F_LLTX can't be changed via Ethtool and is not a feature,
> rather an attribute, very similar to IFF_NO_QUEUE (and hot).
> Free one netdev_features_t bit and make it a private flag.

> Now the LLTX bit sits in the first ("Tx read-mostly") cacheline
> next to netdev_ops, so that the start_xmit locking code will
> potentially read 1 cacheline less, nice.

Are you sure ?

I certainly appreciate the data locality effort but
dev->features is read anyway in TX fast path from netif_skb_features()

Thanks.