netdev - Re: bonding: time limits too tight in bond_ab_arp

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Message-Id: <201208230934.18652.ptesarik@suse.cz>
Date:	Thu, 23 Aug 2012 09:34:18 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	Jay Vosburgh <fubar@...ibm.com>
Cc:	Chris Friesen <chris.friesen@...band.com>,
	Jiri Bohac <jbohac@...e.cz>,
	Andy Gospodarek <andy@...yhouse.net>, netdev@...r.kernel.org
Subject: Re: bonding: time limits too tight in bond_ab_arp_inspect

Dne St 22. srpna 2012 20:42:02 Jay Vosburgh napsal(a):
> Chris Friesen <chris.friesen@...band.com> wrote:
> >On 08/22/2012 11:45 AM, Jiri Bohac wrote:
> >> This code is run from bond_activebackup_arp_mon() about
> >> delta_in_ticks jiffies after the previous ARP probe has been
> >> sent. If the delayed work gets executed exactly in delta_in_ticks
> >> jiffies, there is a chance the slave will be brought up.  If the
> >> delayed work runs one jiffy later, the slave will stay down.
> 
> 	Presumably the ARP reply is coming back in less than one jiffy,
> then, so the slave_last_rx() value is the same jiffy as when the
> _inspect was previously called?

Yes, that's what happens. Keep in mind that the backup slave validates the 
original ARP query, so on a fast network, you get it more or less immediately 
(for my case, I can see a delay of ~70us).

Anyway, why do we have to wait until the next ARP send? Couldn't we simply 
kick the work queue when we receive a valid packet on a down interface?

Petr Tesarik
SUSE Linux
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