netdev - Re: [PATCH v2 net-next] vlan: Add GRO support for non hardware accelerated vlan

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Message-ID: <556C8244.1090400@gmail.com>
Date:	Tue, 02 Jun 2015 01:03:16 +0900
From:	Toshiaki Makita <toshiaki.makita1@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
CC:	"David S . Miller" <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next] vlan: Add GRO support for non hardware accelerated
 vlan

On 15/06/01 (月) 23:12, Eric Dumazet wrote:
> On Mon, 2015-06-01 at 21:55 +0900, Toshiaki Makita wrote:
>
>> @@ -668,6 +753,9 @@ static int __init vlan_proto_init(void)
>>   	if (err < 0)
>>   		goto err5;
>>
>> +	for (i = 0; i < ARRAY_SIZE(vlan_packet_offloads); i++)
>> +		dev_add_offload(&vlan_packet_offloads[i]);
>> +
>>   	vlan_ioctl_set(vlan_ioctl_handler);
>>   	return 0;
>
> My concern about this is :
>
> This might slow down GRO stack for other traffic, if dev_add_offload()
> for vlan offloads is called after
> dev_add_offload(&ip_packet_offload) /
> dev_add_offload(&ipv6_packet_offload)

I didn't have that concern because there are already other similar 
offloads (eth, mpls_uc, mpls_mc). But indeed, they and this could slow 
down GRO stack.

>
>
> This is because list_add_rcu is used and this inserts in front of the
> offload_base list.
>
> void dev_add_offload(struct packet_offload *po)
> {
>          struct list_head *head = &offload_base;
>
>          spin_lock(&offload_lock);
>          list_add_rcu(&po->list, head);
>          spin_unlock(&offload_lock);
> }
>
> Can we ensure offload_base contains a sensible order of expected types ?

Add priority to packet_offload like nf_hook_ops?
Or have dev_add_offload() prioritize IP > IPV6 > others?

Toshiaki Makita
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