Scaling problem with a lot of AF_PACKET sockets on different interfaces

["Vitaly V. Bursov" <vitalyb@telenet.dn.ua>]

Hello,

I have a Linux router with a lot of interfaces (hundreds or
thousands of VLANs) and an application that creates AF_PACKET
socket per interface and bind()s sockets to interfaces.

Each socket has attached BPF filter too.

The problem is observed on linux-3.8.13, but as far I can see
from the source the latest version has alike behavior.

I noticed that box has strange performance problems with
most of the CPU time spent in __netif_receive_skb:
  86.15%  [k] __netif_receive_skb
   1.41%  [k] _raw_spin_lock
   1.09%  [k] fib_table_lookup
   0.99%  [k] local_bh_enable_ip

and this the assembly with the "hot spot":
        │       shr    $0x8,%r15w
        │       and    $0xf,%r15d
   0.00 │       shl    $0x4,%r15
        │       add    $0xffffffff8165ec80,%r15
        │       mov    (%r15),%rax
   0.09 │       mov    %rax,0x28(%rsp)
        │       mov    0x28(%rsp),%rbp
   0.01 │       sub    $0x28,%rbp
        │       jmp    5c7
   1.72 │5b0:   mov    0x28(%rbp),%rax
   0.05 │       mov    0x18(%rsp),%rbx
   0.00 │       mov    %rax,0x28(%rsp)
   0.03 │       mov    0x28(%rsp),%rbp
   5.67 │       sub    $0x28,%rbp
   1.71 │5c7:   lea    0x28(%rbp),%rax
   1.73 │       cmp    %r15,%rax
        │       je     640
   1.74 │       cmp    %r14w,0x0(%rbp)
        │       jne    5b0
  81.36 │       mov    0x8(%rbp),%rax
   2.74 │       cmp    %rax,%r8
        │       je     5eb
   1.37 │       cmp    0x20(%rbx),%rax
        │       je     5eb
   1.39 │       cmp    %r13,%rax
        │       jne    5b0
   0.04 │5eb:   test   %r12,%r12
   0.04 │       je     6f4
        │       mov    0xc0(%rbx),%eax
        │       mov    0xc8(%rbx),%rdx
        │       testb  $0x8,0x1(%rdx,%rax,1)
        │       jne    6d5

This corresponds to:

net/core/dev.c:
         type = skb->protocol;
         list_for_each_entry_rcu(ptype,
                         &ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {
                 if (ptype->type == type &&
                     (ptype->dev == null_or_dev || ptype->dev == skb->dev ||
                      ptype->dev == orig_dev)) {
                         if (pt_prev)
                                 ret = deliver_skb(skb, pt_prev, orig_dev);
                         pt_prev = ptype;
                 }
         }

Which works perfectly OK until there are a lot of AF_PACKET sockets, since
the socket adds a protocol to ptype list:

# cat /proc/net/ptype
Type Device      Function
0800 eth2.1989 packet_rcv+0x0/0x400
0800 eth2.1987 packet_rcv+0x0/0x400
0800 eth2.1986 packet_rcv+0x0/0x400
0800 eth2.1990 packet_rcv+0x0/0x400
0800 eth2.1995 packet_rcv+0x0/0x400
0800 eth2.1997 packet_rcv+0x0/0x400
.......
0800 eth2.1004 packet_rcv+0x0/0x400
0800          ip_rcv+0x0/0x310
0011          llc_rcv+0x0/0x3a0
0004          llc_rcv+0x0/0x3a0
0806          arp_rcv+0x0/0x150

And this obviously results in a huge performance penalty.

ptype_all, by the looks, should be the same.

Probably one way to fix this it to perform interface name matching in
af_packet handler, but there could be other cases, other protocols.

Ideas are welcome :)

-- 
Thanks
Vitaly