netdev - Re: [PATCHv2 net] bonding: discard lowest hash bit for 802.3ad layer3+4

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Message-Id: <20171108.113013.2184085922808970912.davem@davemloft.net>
Date:   Wed, 08 Nov 2017 11:30:13 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     liuhangbin@...il.com
Cc:     netdev@...r.kernel.org, pabeni@...hat.com, edumazet@...gle.com
Subject: Re: [PATCHv2 net] bonding: discard lowest hash bit for 802.3ad
 layer3+4

From: Hangbin Liu <liuhangbin@...il.com>
Date: Mon,  6 Nov 2017 09:01:57 +0800

> After commit 07f4c90062f8 ("tcp/dccp: try to not exhaust ip_local_port_range
> in connect()"), we will try to use even ports for connect(). Then if an
> application (seen clearly with iperf) opens multiple streams to the same
> destination IP and port, each stream will be given an even source port.
> 
> So the bonding driver's simple xmit_hash_policy based on layer3+4 addressing
> will always hash all these streams to the same interface. And the total
> throughput will limited to a single slave.
> 
> Change the tcp code will impact the whole tcp behavior, only for bonding
> usage. Paolo Abeni suggested fix this by changing the bonding code only,
> which should be more reasonable, and less impact.
> 
> Fix this by discarding the lowest hash bit because it contains little entropy.
> After the fix we can re-balance between slaves.
> 
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>

Applied and queued up for -stable, thank you.