RE: ipgre rss is broken since gro

-----Original Message-----
From: Eric Dumazet [mailto:edumazet@google.com]
Sent: Monday, December 10, 2012 1:27 AM
To: Dmitry Kravkov
Cc: netdev@vger.kernel.org
Subject: Re: ipgre rss is broken since gro

On Sun, Dec 9, 2012 at 12:49 PM, Dmitry Kravkov [off-list ref]
wrote:

quoted

for this item: drop_watch does not show any drops (i've disable all
other interfaces for clear env)
I will explain a little bit more the setup:
bnx2x device (under testing) is configured for RSS for IPGRE packets.
Sending multiple (3) TCP_STREAM causes ip_gre interface to disappear
packets (even ICMP).
This is not happening with single TCP_STREAM, or before gro_cell
introduction.

I dont know, I tried a bnx2x setup, and 100 tcp flows, no special problem.

Current bnx2x do not apply RSS for GRE, non GRE RSS is working w/o problem.

If you receive a lot of packets on a single RX queue, they might be
dropped because cpu cant cope with the load
(This has nothing to do with GRE or GRO )

CPU is not loaded at all 

cat /proc/net/softnet_stat

Please find attached.

For gre interface RX and DROP statistics are advancing simultaneously (by one each ICMP request):

[root@ ~]# ifconfig gre
gre       Link encap:UNSPEC  HWaddr C0-A8-0A-40-73-72-83-D2-00-00-00-00-00-00-00-00
          inet addr:8.0.0.1  P-t-P:8.0.0.1  Mask:255.255.255.0
          inet6 addr: fe80::5efe:c0a8:a40/64 Scope:Link
          UP POINTOPOINT RUNNING NOARP  MTU:1476  Metric:1
          RX packets:1646824 errors:0 dropped:51610 overruns:0 frame:0
          TX packets:140519 errors:1 dropped:0 overruns:0 carrier:1
          collisions:0 txqueuelen:0
          RX bytes:2357650904 (2.1 GiB)  TX bytes:7309072 (6.9 MiB)

[root@ ~]# ifconfig gre
gre       Link encap:UNSPEC  HWaddr C0-A8-0A-40-73-72-83-82-00-00-00-00-00-00-00-00
          inet addr:8.0.0.1  P-t-P:8.0.0.1  Mask:255.255.255.0
          inet6 addr: fe80::5efe:c0a8:a40/64 Scope:Link
          UP POINTOPOINT RUNNING NOARP  MTU:1476  Metric:1
          RX packets:1646826 errors:0 dropped:51612 overruns:0 frame:0
          TX packets:140519 errors:1 dropped:0 overruns:0 carrier:1
          collisions:0 txqueuelen:0
          RX bytes:2357651072 (2.1 GiB)  TX bytes:7309072 (6.9 MiB) 

[root@ ~]# tcpdump -i gre
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on gre, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel
2 packets dropped by interface