netdev - RE: [PATCH v3 net-next 3/6] net: Add SW fallback infrastructure for offloaded sockets

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Date:   Tue, 19 Dec 2017 07:51:02 +0000
From:   Ilya Lesokhin <ilyal@...lanox.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "davejwatson@...com" <davejwatson@...com>,
        "tom@...bertland.com" <tom@...bertland.com>,
        "hannes@...essinduktion.org" <hannes@...essinduktion.org>,
        Boris Pismenny <borisp@...lanox.com>,
        "Aviad Yehezkel" <aviadye@...lanox.com>,
        Liran Liss <liranl@...lanox.com>,
        "Steffen Klassert" <steffen.klassert@...unet.com>
Subject: RE: [PATCH v3 net-next 3/6] net: Add SW fallback infrastructure for
 offloaded sockets

On Monday, December 18, 2017 9:18 PM, Marcelo Ricardo Leitner wrote:

> > +
> > +	if (sk && sk_fullsock(sk) && sk->sk_offload_check)
> 
> Isn't this going to hurt the fast path, checking for sk fields here?
> 

We do add code to the fast path but it seems unavoidable if you want to have SW fallback.
The XFRM device offload also does that
http://elixir.free-electrons.com/linux/v4.14.7/source/net/core/dev.c#L3058

The check can be optimized but I didn't want to do that before I saw that it's an issue.
I'm also not sure what the correct solution is.
I don't like that fact that each "stateful protocol" we offload requires its own check. 
We need to think if we can find a generic way of doing it.

Perhaps we can hold the expected netdev somewhere in the SKB and only if we don't
Go out of the expected netdev go to a slow path that does a check for each protocol.

Thanks,
Ilya