From: Chris Friesen <chris.friesen@genband•com>
To: Jay Vosburgh <fubar@us•ibm.com>
Cc: Jiri Bohac <jbohac@suse•cz>, Andy Gospodarek <andy@greyhouse•net>,
netdev@vger•kernel.org, Petr Tesarik <ptesarik@suse•cz>
Subject: Re: bonding: time limits too tight in bond_ab_arp_inspect
Date: Wed, 22 Aug 2012 12:58:24 -0600 [thread overview]
Message-ID: <50352BD0.3060409@genband.com> (raw)
In-Reply-To: <24655.1345660922@death.nxdomain>
On 08/22/2012 12:42 PM, Jay Vosburgh wrote:
> Chris Friesen<chris.friesen@genband•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?
>
>> <snip>
>>
>>> Should they perhaps all be increased by, say, delta_in_ticks/2, to make this
>>> less dependent on the current scheduling latencies?
>>
>> We have been using a patch that tracks the arpmon requested sleep time vs
>> the actual sleep time and adds any scheduling latency to the allowed
>> delta. That way if we sleep too long due to scheduling latency it doesn't
>> affect the calculation.
>
> How much scheduling latency do you see?
>
> Is that really better than just permitting a bit more slack in
> the timing window?
We hit enough latency that it triggered arpmon to falsely mark multiple
links as lost. This triggered our system maintenance code to go into a
"oh no we can't talk to the outside world" secenario, which does fairly
intrusive things to try and bring connectivity back up. Basically a bad
thing to happen just because of a random scheduler latency spike.
I should note that we added this some time back and are still running
older kernels so I have no idea what latency on modern kernels is like.
Chris
next prev parent reply other threads:[~2012-08-22 19:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-22 17:45 bonding: time limits too tight in bond_ab_arp_inspect Jiri Bohac
2012-08-22 17:54 ` Chris Friesen
2012-08-22 18:42 ` Jay Vosburgh
2012-08-22 18:58 ` Chris Friesen [this message]
2012-08-23 7:34 ` Petr Tesarik
2012-08-30 22:02 ` [PATCH] bonding: add some slack to arp monitoring time limits Jiri Bohac
2012-08-31 20:37 ` David Miller
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