Re: [PATCH 0/4] Fix routing metrics

[David Miller <davem@davemloft.net>]

From: Steffen Klassert <steffen.klassert@secunet.com>
Date: Wed, 8 Feb 2012 08:30:37 +0100

> On Mon, Feb 06, 2012 at 03:29:16PM -0500, David Miller wrote:
>> 
>> Thinking about this, it seems overkill to check this on every metric
>> access.
>> 
>> You have an opportunity to validate metrics when the peer is bound to
>> the route.
>> 
>> This is because any change to the FIB metrics, is in turn a change
>> to the FIB, which therefore invalidates the entire routing cache.
>> 
>> So you can be sure that a new route cache entry will be created, and
>> at that creation time you can ensure that we'll respect the updated
>> FIB metrics if encessary.
> 
> Not sure if I get you right here, but that's what this patchset
> does. It invalidates the metrics on the peer by incrementing
> peer_genid in rt_cache_invalidate() which is invoked on every FIB
> change. Then, on slowpath route lookup it checks in rt_init_metrics()
> whether the peer_genid changed. If it changed, it exchanges the
> invalidated merics with new ones and copies the informations from
> the FIB into it.

If the routing cache is invalided, you'll "see" this updated inetpeer
because every single routing cache entry will get rebuilt.