Re: [PATCH net-next 3/5] netdev_features: convert NETIF_F_LLTX to dev->lltx

From: Eric Dumazet <edumazet@google.com>
Date: Tue, 25 Jun 2024 16:00:51 +0200

On Tue, Jun 25, 2024 at 1:50 PM Alexander Lobakin
[off-list ref] wrote:

quoted

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.

quoted

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()

Ah, right. I though netif_skb_features() happens a bit later than locking.
Anyway, this patch is not about cachelines, but freeing 1
netdev_features_t bit. I can remove this paragraph if it may confuse people.

Thanks,
Olek