netdev - Re: [PATCH net-next v3 2/3] net/macsec: Add MACsec skb extension Rx Data path support

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Date:   Tue, 21 Jun 2022 12:26:41 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lior Nahmanson <liorna@...dia.com>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Raed Salem <raeds@...dia.com>, Jiri Pirko <jiri@...dia.com>,
        Ben Ben Ishay <benishay@...dia.com>
Subject: Re: [PATCH net-next v3 2/3] net/macsec: Add MACsec skb extension Rx
 Data path support

On Tue, 21 Jun 2022 12:39:23 +0000 Lior Nahmanson wrote:
> > Shooting from the hip a little bit, but macsec being a tightly bound L2 upper
> > maybe metadata dst is a workable solution for carrying the sci and offload
> > status between upper and lower? The range of values should be well known
> > and limited.  
> 
> Under the assumption that by skb_metadata you meant metadata_dst,

Can you show me in my email where I said skb_metadata?

> I think there are few reasons why i think is better to use skb extensions:
> 
> 1. Unlike skb extension, the metadata_dst deallaction is handled directly by the allocator.
> Since the sci and offloaded fields are shared between the MACsec driver and the offload driver
> (in our case mlx5 driver), for Rx, the metadata_dst allocation is done in the mlx5 driver,
> while the dealloction should be done in the MACsec driver.
> This is undesired behavior.

You allocate metadata skb once and then attach it to the skbs.

> 2. medadata_dst is attached to the skb using skb_dst_set(), which set the slow_gro bit.
> So there is no gain regarding slow_gro flow.
> 
> 3. metadata_dst allocation require much more memory than needed for MACsec use case
> (mainly because struct dst_entry which seems redundant for this case).