Date:	Wed, 02 Feb 2011 09:57:33 -0800
From:	Jay Vosburgh <fubar@...ibm.com>
To:	=?UTF-8?B?Tmljb2xhcyBkZSBQZXNsb8O8YW4=?= 
	<nicolas.2p.debian@...il.com>
cc:	"Oleg V. Ukhno" <olegu@...dex-team.ru>,
	John Fastabend <john.r.fastabend@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] bonding: added 802.3ad round-robin hashing policy for single TCP session balancing

Nicolas de Pesloüan <nicolas.2p.debian@...il.com> wrote:

>Le 29/01/2011 03:28, Jay Vosburgh a écrit :
>> 	I've thought about this whole thing, and here's what I view as
>> the proper way to do this.
>>
>> 	In my mind, this proposal is two separate pieces:
>>
>> 	First, a piece to make round-robin a selectable hash for
>> xmit_hash_policy.  The documentation for this should follow the pattern
>> of the "layer3+4" hash policy, in particular noting that the new
>> algorithm violates the 802.3ad standard in exciting ways, will result in
>> out of order delivery, and that other 802.3ad implementations may or may
>> not tolerate this.
>>
>> 	Second, a piece to make certain transmitted packets use the
>> source MAC of the sending slave instead of the bond's MAC.  This should
>> be a separate option from the round-robin hash policy.  I'd call it
>> something like "mac_select" with two values: "default" (what we do now)
>> and "slave_src_mac" to use the slave's real MAC for certain types of
>> traffic (I'm open to better names; that's just what I came up with while
>> writing this).  I believe that "certain types" means "everything but
>> ARP," but might be "only IP and IPv6."  Structuring the option in this
>> manner leaves the option open for additional selections in the future,
>> which a simple "on/off" option wouldn't.  This option should probably
>> only affect a subset of modes; I'm thinking anything except balance-tlb
>> or -alb (because they do funky MAC things already) and active-backup (it
>> doesn't balance traffic, and already uses fail_over_mac to control
>> this).  I think this option also needs a whole new section down in the
>> bottom explaining how to exploit it (the "pick special MACs on slaves to
>> trick switch hash" business).
>>
>> 	Comments?
>
>Looks really sensible to me.
>
>I just propose the following option and option values : "src_mac_select"
>(instead of mac_select), with "default" and "slave_mac" (instead of
>slave_src_mac) as possible values. In the future, we might need a
>"dst_mac_select" option... :-)

	I originally thought of using the nomenclature you propose; my
thinking for doing it the way I ended up with is to minimize the number
of tunable knobs that bonding has (so, the dst_mac would be a setting
for mac_select).  That works as long as there aren't a lot of settings
that would be turned on simultaneously, since each combination would
have to be a separate option, or the options parser would have to handle
multiple settings (e.g., mac_select=src+dst or something like that).

	Anyway, after thinking about it some more, in the long run it's
probably safer to separate these two, so, Oleg, use the above naming
("src_mac_select" with "default" and "slave_mac").

>Also, are there any risks that this kind of session load-balancing won't
>properly cooperate with multiqueue (as explained in "Overriding
>Configuration for Special Cases" in Documentation/networking/bonding.txt)?
>I think it is important to ensure we keep the ability to fine tune the
>egress path selection

	I think the logic for the mac_select (or src_mac_select or
whatever) just has to be done last, after the slave selection is done by
the multiqueue stuff.  That's probably a good tidbit to put in the
documentation as well.

	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
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