netdev - Re: [PATCH] bonding: added 802.3ad round-robin hashing policy for single TCP session balancing

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Date:	Tue, 18 Jan 2011 18:28:48 +0300
From:	"Oleg V. Ukhno" <olegu@...dex-team.ru>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
CC:	John Fastabend <john.r.fastabend@...el.com>,
	Jay Vosburgh <fubar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Sébastien Barré <sebastien.barre@...ouvain.be>,
	Christophe Paasch <christoph.paasch@...ouvain.be>
Subject: Re: [PATCH] bonding: added 802.3ad round-robin hashing policy for
 single TCP session balancing

On 01/18/2011 05:54 PM, Nicolas de Pesloüan wrote:
> Le 18/01/2011 13:40, Oleg V. Ukhno a écrit :
>
> The fact that there exist many situations where it simply doesn't work,
> should not cause the idea of Oleg to be rejected.
>
> In Documentation/networking/bonding.txt, tuning tcp_reordering on
> receiving side is already documented as a possible workaround for out of
> order delivery due to load balancing of a single TCP session, using
> mode=balance-rr.
>
> This might work reasonably well in a pure LAN topology, without any
> router between both ends of the TCP session, even if this is limited to
> Linux hosts. The uses are not uncommon and not limited to iSCSI:
> - between an application server and a database server,
> - between members of a cluster, for replication purpose,
> - between a server and a backup system,
> - ...
Nicolas, thank you for your opinion - this is exactly what I mean - 
iSCSI is just one particular use case, but there are many cases where 
this load balancing method will be useful
>
> Of course, for longer paths, with routers and variable RTT, we would
> need something different (possibly MultiPathTCP:
> http://datatracker.ietf.org/wg/mptcp/).
>
> I remember a topology (described by Jay, for as far as I remember),
> where two hosts were connected through two distinct VLANs. In such
> topology:
> - it is possible to detect path failure using arp monitoring instead of
> miimon.
> - changing the destination MAC address of egress packets are not
> necessary, because egress path selection force ingress path selection
> due to the VLAN.

In case with two VLANs - yes, this shouldn't be necessary(but needs to 
be tested, I am not sure), but within one - it is essential for correct 
rx load striping.
>
> I think the only point is whether we need a new xmit_hash_policy for
> mode=802.3ad or whether mode=balance-rr could be enough.
May by, but it seems to me fair enough not to restrict this feature only 
to non-LACP aggregate links; dynamic aggregation may be useful(it helps 
to avoid switch misconfiguration(misconfigured slaves on switch side) 
sometimes without loss of service).
>
> Oleg, would you mind trying the above "two VLAN" topology" with
> mode=balance-rr and report any results ? For high-availability purpose,
> it's obviously necessary to setup those VLAN on distinct switches.
I'll do it, but it will take some time to setup test environment, 
several days may be.
You mean following topology:
           switch 1
        /           \
host A                host B
        \  switch 2 /

(i'm sure it will work as desired if each host is connected to each 
switch with only one slave link, if there are more slaves in each switch 
- unsure)?
>
> Nicolas
>
>
>


-- 
Best regards,
Oleg Ukhno.
ITO Team Lead,
Yandex LLC.



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