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

Alexander Lobakin
2024-06-26T08:54:39Z

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
> <aleksander.lobakin@intel.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()

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