No, he means the physical interface needs a larger MTU than the logical one. The physical one has to transport the packets your logical interface accepts plus the header data for GRE. If there isn't enough headroom then it must split the packet in two and reassemble at the far end - a slow process.
Chris. > -----Original Message----- > From: discuss-boun...@openvswitch.org [mailto:discuss- > boun...@openvswitch.org] On Behalf Of Li, Chen > Sent: Monday, January 06, 2014 22:23 > To: Jesse Gross > Cc: discuss@openvswitch.org > Subject: Re: [ovs-discuss] low bandwidth for gre > > Sorry, I'm really new to network area. > > So, you mean I should keep the sender under the low MTU, while the > receiver with higher MTU size ?? > > But, how I can make sure the sender is always the sender ???? > > Thanks. > -chen > > -----Original Message----- > From: Jesse Gross [mailto:je...@nicira.com] > Sent: Tuesday, January 07, 2014 11:20 AM > To: Li, Chen > Cc: discuss@openvswitch.org > Subject: Re: [ovs-discuss] low bandwidth for gre > > If you change the MTU of both interfaces then it will still result in > fragmentation. > > On Mon, Jan 6, 2014 at 9:50 PM, Li, Chen <chen...@intel.com> wrote: > > Yes, fragmentation do affect the bandwidth. > > > > I run command to change interfaces' MTU size to test if fragmentation > makes a difference. > > ifconfig eth4 mtu ${mtu_size} > > ifconfig br-int mtu ${mtu_size} > > > > The default MTU = 1500 => 122 Kbits/sec > > MTU = 3000 => 419 Kbits/sec > > MTU = 6000 => 780 Kbits/sec > > MTU = 9000 => 1.14 Mbits/sec > > > > > > But, what I don’t understand is, I didn’t see really high CPU%. > > > > Also, there is no other way to improve the bandwidth ? > > Even under MTU=9000, 1.14 Mb/s vs. 10 Gb/s, the gap between the test > result we can get and the physical NIC is unacceptable!! > > > > > > Thanks. > > -chen > > > > > > -----Original Message----- > > From: Jesse Gross [mailto:je...@nicira.com] > > Sent: Tuesday, January 07, 2014 10:32 AM > > To: Li, Chen > > Cc: discuss@openvswitch.org > > Subject: Re: [ovs-discuss] low bandwidth for gre > > > > Well did you at least see if fragmentation makes a difference? > > > > On Mon, Jan 6, 2014 at 8:14 PM, Li, Chen <chen...@intel.com> wrote: > >> But 122 Kbits/s vs. 9.41Gb/s ?? > >> > >> Is this correct ??? > >> > >> How can I improve it ?? > >> > >> > >> Thanks. > >> -chen > >> > >> > >> -----Original Message----- > >> From: Jesse Gross [mailto:je...@nicira.com] > >> Sent: Tuesday, January 07, 2014 12:24 AM > >> To: Li, Chen > >> Cc: discuss@openvswitch.org > >> Subject: Re: [ovs-discuss] low bandwidth for gre > >> > >> On Sun, Jan 5, 2014 at 11:58 PM, Li, Chen <chen...@intel.com> wrote: > >>> Hi list, > >>> > >>> > >>> > >>> I’m working under CentOS, so the kernel is > >>> 2.6.32-358.123.2.openstack.el6.x86_64. > >>> > >>> openvswitch.x86_64 1.11.0_8ce28d-1.el6ost > >>> > >>> > >>> > >>> I have two physical machine in the test, each of them have a 10 Gb NIC > card. > >>> > >>> The bandwidth between the two machine using iperf can achieve > 9.41Gb/s. > >>> > >>> > >>> > >>> After enable gre follow guide > >>> http://networkstatic.net/configuring-vxlan-and-gre-tunnels-on-openvs > >>> w > >>> i > >>> tch/#!prettyPhoto > >>> > >>> The bandwitdth between the two nodes are really low. > >>> > >>> Only 122 Kbits/s !!!! > >> > >> At a minimum, fragmentation is presumably occurring. > _______________________________________________ > discuss mailing list > discuss@openvswitch.org > http://openvswitch.org/mailman/listinfo/discuss _______________________________________________ discuss mailing list discuss@openvswitch.org http://openvswitch.org/mailman/listinfo/discuss
