netdev - Re: [PATCH net-next V6 02/14] bridge: Add vlan filtering infrastructure

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Message-ID: <CAHXqBFKg6Vp5=dprDYKON2LmshhX+nSPF7KRHiQmOS68PrQq-A@mail.gmail.com>
Date:	Fri, 18 Jan 2013 02:57:14 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	Vlad Yasevich <vyasevic@...hat.com>
Cc:	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
	davem@...emloft.net, shemminger@...tta.com, mst@...hat.com,
	shmulik.ladkani@...il.com
Subject: Re: [PATCH net-next V6 02/14] bridge: Add vlan filtering infrastructure

2013/1/16 Vlad Yasevich <vyasevic@...hat.com>:
[...]
> --- /dev/null
> +++ b/net/bridge/br_vlan.c
[...]
> +struct net_port_vlan *nbp_vlan_find(const struct net_port_vlans *v, u16 vid)
> +{
> +       struct net_port_vlan *pve;
> +
> +       /* Must be done either in rcu critical section or with RTNL held */
> +       WARN_ON_ONCE(!rcu_read_lock_held() && !rtnl_is_locked());
> +
> +       list_for_each_entry_rcu(pve, &v->vlan_list, list) {
> +               if (pve->vid == vid)
> +                       return pve;
> +       }
> +
> +       return NULL;
> +}

This looks expensive - it's O(n) with n = number of configured VLANs on a port.
And this is called for every packet. The bridge already has a hash of VLAN
structures found by br_vlan_find(). You could add a second bitmap there
(eg. ingres_ports[]) and check port's bit instead of walking the list.
You would use a bit more memory (64 bytes minus the removed list-head)
per configured VLAN but save some cycles in hot path.

Best Regards,
Michał Mirosław
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