netdev - Re: [PATCH net-next 1/4] nexthop: Factor out hash threshold fdb nexthop selection

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Date: Wed, 19 Jul 2023 13:54:40 +0000
From: Benjamin Poirier <bpoirier@...dia.com>
To: David Ahern <dsahern@...nel.org>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Shuah Khan
	<shuah@...nel.org>, "linux-kselftest@...r.kernel.org"
	<linux-kselftest@...r.kernel.org>, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 1/4] nexthop: Factor out hash threshold fdb
 nexthop selection

On 2023-05-30 08:57 -0600, David Ahern wrote:
> On 5/29/23 2:19 PM, Benjamin Poirier wrote:
> > diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> > index f95142e56da0..27089dea0ed0 100644
> > --- a/net/ipv4/nexthop.c
> > +++ b/net/ipv4/nexthop.c
> > @@ -1152,11 +1152,31 @@ static bool ipv4_good_nh(const struct fib_nh *nh)
> >  	return !!(state & NUD_VALID);
> >  }
> >  
> > +static struct nexthop *nexthop_select_path_fdb(struct nh_group *nhg, int hash)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < nhg->num_nh; i++) {
> > +		struct nh_grp_entry *nhge = &nhg->nh_entries[i];
> > +
> > +		if (hash > atomic_read(&nhge->hthr.upper_bound))
> > +			continue;
> > +
> > +		return nhge->nh;
> > +	}
> > +
> > +	WARN_ON_ONCE(1);
> 
> I do not see how the stack is going to provide useful information; it
> should always be vxlan_xmit ... nexthop_select_path_fdb, right?

Not always, it is also possible to have a resilient nhg with fdb
nexthops. In that case, nexthop_select_path_fdb() is not called. In
practice, I tried such a configuration and it does not work well. I have
prepared a fix that I'll send after the current series has been dealt
with.

Sorry for the long delay before my reply.