bird under heavy cpu load

[Alexander V. Chernikov]

On 12.03.2012 19:22, Oleg wrote:
> On Mon, Mar 12, 2012 at 02:27:23PM +0400, Alexander V. Chernikov wrote:
>> On 12.03.2012 13:25, Oleg wrote:
>>> Hi, all.
>>>
>>> I have some experience with bird under heavy cpu load. I had a
>>> situation when bird do frequent updates of kernel table, because
>>> of bgp-session frequent down/up (because of cpu and/or net load).
>>> I waited about 5-10 minutes for birdc started, when i wanted to
>>> reconfigure bird with configure soft command from birdc(ssh and
>>> other interactive programs works well). After i changed bird.conf
>>> in such a way that i get from upstream 0.0.0.0/0 instead of full view
>>> birdc worked fine and bird cpu load lowered(before, bird load cpu about
>>> 30-89%).
>>> What can i do in such situtation in future for birdc normal work?
>> Adding/removing kernel routes is a complex task, results in main
>> process waiting for system call is completed.
>>
>> It is very costy and one (developer) possibility is to add
>> additional thread which does kernel interaction.
>
>    I think that a separate thread can solve this nuisance.
>
>> We workaround this by installing IGP routes only (which does not
>> help for border router)
>
>    Unfortunately, this is a border router.
>
>> You can try to reduce MAX_RX_STEPS to 1 in sysdep/unix/io.c, this
>> will help a bit for new route installation (2 minutes instead of 5),
>
>    Thanks! I'll try it.
>
>> but at the moment answer seems to be "don't export all routes to
>> kernel". You can filter all that is>=/20, for example, to provide
>> reasonable load balancing with much less routes in OS kernel.
>
>    In simple configuration with one upstream this works fine, but what in more
> complex configurations? Can i lose some networks? Or can i get poor ping,
> because of /24 prefix, for example, is better than /20 that contain it?
You should leave default route from one (or both) your uplinks, so no 
connectivity should be lost. You still achieve some kind of load 
balancing for outgoing traffic, however it may not follow suboptimal path.

>
>>> And additional two questions:
>>> Does bird immediately push routes info in kernel table, if it receive routes
>>> updates from bgp-peer or it wait for the next kernel table scan?
>> Kernel protocol (just as any other protocol) receives route updates
>> immediately after they are announced to the routing table by BGP
>> protocol instance. In the came callback kernel update (for the
>> single route) is prepared and called.
>
>    So, in a such situation a simply increasing of a scan time value doesn't
> help as i understand.
>