netdev - Re: [net-next,1/2] net: Set sk_txhash from a random number

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Message-ID: <1449580559.7632.10.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 08 Dec 2015 05:15:59 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Drozdov <al.drozdov@...il.com>
Cc:	Tom Herbert <tom@...bertland.com>, davem@...emloft.net,
	netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [net-next,1/2] net: Set sk_txhash from a random number

On Tue, 2015-12-08 at 11:33 +0300, Alexander Drozdov wrote:
> 29.07.2015 02:02, Tom Herbert wrote:
> > This patch creates sk_set_txhash and eliminates protocol specific
> > inet_set_txhash and ip6_set_txhash. sk_set_txhash simply sets a
> > random number instead of performing flow dissection. sk_set_txash
> > is also allowed to be called multiple times for the same socket,
> > we'll need this when redoing the hash for negative routing advice.
> It seems that this patch and some previous txhash-related
> ones break af_packet hash features for outgoing packets:
> - PACKET_FANOUT_HASH
> - TP_FT_REQ_FILL_RXHASH
> 
> af_packet now thinks that hashes for for incoming and outgoing
> packets of the same TCP stream differ. That is true for TCP
> sessions initiated by the host.

There never has been such guarantee. Even rx hashes for a single TCP
flow can differ, if packets are received on two different NIC with
different RSSS keys.



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