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

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Message-ID: <CALx6S36u4=1f2WAPhgG_t9oxZSK75uR_hK28=HR_2FibUN9amQ@mail.gmail.com>
Date:	Tue, 8 Dec 2015 08:33:17 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Alexander Drozdov <al.drozdov@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Kernel Team <kernel-team@...com>
Subject: Re: [net-next,1/2] net: Set sk_txhash from a random number

On Tue, Dec 8, 2015 at 5:15 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 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.
>
+1, it is a salient property that hashes can differ in each direction
for a flow and that the hash for a flow can change over time.

>
>
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