netdev - Re: [PATCH RFC net-next 01/13] net: bridge: add control of bum flooding to bridge itself

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Date:   Wed, 13 Apr 2022 12:58:31 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Joachim Wiberg <troglobit@...il.com>,
        Roopa Prabhu <roopa@...dia.com>
Cc:     netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH RFC net-next 01/13] net: bridge: add control of bum
 flooding to bridge itself

On 13/04/2022 12:51, Joachim Wiberg wrote:
> On Tue, Apr 12, 2022 at 21:27, Nikolay Aleksandrov <razor@...ckwall.org> wrote:
>> On 11/04/2022 16:38, Joachim Wiberg wrote:
>>> @@ -526,6 +526,10 @@ void br_dev_setup(struct net_device *dev)
>>>  	br->bridge_ageing_time = br->ageing_time = BR_DEFAULT_AGEING_TIME;
>>>  	dev->max_mtu = ETH_MAX_MTU;
>>> +	br_opt_toggle(br, BROPT_UNICAST_FLOOD, 1);
>> This one must be false by default. It changes current default behaviour.
>> Unknown unicast is not currently passed up to the bridge if the port is
>> not in promisc mode, this will change it. You'll have to make it consistent
>> with promisc (e.g. one way would be for promisc always to enable unicast flood
>> and it won't be possible to be disabled while promisc).
> 
> Ouch, my bad!  Will look into how to let this have as little impact as
> possible.  I like your semantics there, promisc should always win.
> 
>>> +	br_opt_toggle(br, BROPT_MCAST_FLOOD, 1);
>>> +	br_opt_toggle(br, BROPT_BCAST_FLOOD, 1);
>>
>> s/1/true/ for consistency
> 
> Of course, thanks!
> 
>>> @@ -118,7 +118,8 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
>>>  		/* by definition the broadcast is also a multicast address */
>>>  		if (is_broadcast_ether_addr(eth_hdr(skb)->h_dest)) {
>>>  			pkt_type = BR_PKT_BROADCAST;
>>> -			local_rcv = true;
>>> +			if (br_opt_get(br, BROPT_BCAST_FLOOD))
>>> +				local_rcv = true;
>>>  		} else {
>>>  			pkt_type = BR_PKT_MULTICAST;
>>>  			if (br_multicast_rcv(&brmctx, &pmctx, vlan, skb, vid))
>>> @@ -161,12 +162,16 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
>>>  			}
>>>  			mcast_hit = true;
>>>  		} else {
>>> -			local_rcv = true;
>>> -			br->dev->stats.multicast++;
>>> +			if (br_opt_get(br, BROPT_MCAST_FLOOD)) {
>>> +				local_rcv = true;
>>> +				br->dev->stats.multicast++;
>>> +			}
>>>  		}
>>>  		break;
>>>  	case BR_PKT_UNICAST:
>>>  		dst = br_fdb_find_rcu(br, eth_hdr(skb)->h_dest, vid);
>>> +		if (!dst && br_opt_get(br, BROPT_UNICAST_FLOOD))
>>> +			local_rcv = true;
>>>  		break;
>>
>> This adds new tests for all fast paths for host traffic, especially
>> the port - port communication which is the most critical one.  Please
>> at least move the unicast test to the "else" block of "if (dst)"
>> later.
> 
> OK, will fix!
> 
>> The other tests can be moved to host only code too, but would require
>> bigger changes.  Please try to keep the impact on the fast-path at
>> minimum.
> 
> Interesting, you mean by speculatively setting local_rcv = true and
> postpone the decsion to br_pass_frame_up(), right?  Yeah that would
> indeed be a bit more work.

Yes, I was thinking maybe local_rcv can become an enum with an exact reason for the
local_rcv, so if it's > 0 do the local_rcv and br_pass_frame_up() then
can make a proper decision without passing all of the vars. I haven't tried it,
so not sure if it's feasible. :)