netdev - Re: Get rxhash fixes and RFS support in tun

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Message-Id: <20131120.215025.590189385589840672.davem@davemloft.net>
Date:	Wed, 20 Nov 2013 21:50:25 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	therbert@...gle.com
Cc:	netdev@...r.kernel.org, edumazet@...gle.com, hkchu@...gle.com
Subject: Re: Get rxhash fixes and RFS support in tun

From: Tom Herbert <therbert@...gle.com>
Date: Wed, 20 Nov 2013 18:42:48 -0800

> We need the rxhash to be the value seen at the point of RPS (to do RFS
> correctly), which I think probably means we don't ever want to change
> it after the first calculation! (clearing at tunnel decap wouldn't be
> correct either)  For ESP or AH, I believe it's appropriate to use SPI
> as a substitute for ports.

But that means that all connections going over the same IPSEC path
hash to the same value.

I really think that xfrm_input() should zap the rxhash near the
existing nf_reset() call.

The same argument goes for tunnels, that is why ip_tunnel_core.c does
what it does with the rxhash clearing right now.

In both the IPSEC tunnel (not transport) and normal IP/GRE tunnel
cases, it's a completely new SKB receive, done via netif_rx(), after
decapsulation.

That leaves only IPSEC transport mode as the only case where RFS isn't
(re-)performed but we can build infrastructure to make that happen.
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