netdev - Re: [PATCH 0/4] Fix routing metrics

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Message-ID: <20120209124411.GJ23142@secunet.com>
Date:	Thu, 9 Feb 2012 13:44:11 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	David Miller <davem@...emloft.net>
Cc:	timo.teras@....fi, netdev@...r.kernel.org
Subject: Re: [PATCH 0/4] Fix routing metrics

On Wed, Feb 08, 2012 at 03:18:37PM -0500, David Miller wrote:
> From: Steffen Klassert <steffen.klassert@...unet.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.

Hm, I still don't get your point. Could you specify this please?

When a route cache entry is created and the peer_genid does not match
the genid on the inetpeer, fresh inetpeer metrics are allocated  and
then published. After that, the new metrics are in proper state and
ready to use.
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