On Fri, Nov 16, 2012 at 1:00 PM, Kyle Mestery (kmestery) <kmest...@cisco.com> wrote: > On Nov 15, 2012, at 3:32 PM, Kyle Mestery (kmestery) <kmest...@cisco.com> > wrote: >> On Nov 15, 2012, at 3:13 PM, Kyle Mestery (kmestery) <kmest...@cisco.com> >> wrote: >>> On Nov 15, 2012, at 1:03 PM, Kyle Mestery (kmestery) <kmest...@cisco.com> >>> wrote: >>>> Jesse: >>>> >>>> I modified the source port hashing for the VXLAN patch I submitted a few >>>> days ago, >>>> but I've noticed when using the upstream source port hashing routine, >>>> performance >>>> drops off by 3.5 times when using iperf between two VMs. From what I can >>>> tell, it >>>> has to be that all skbuffs coming into the VXLAN tunnel have not already >>>> had their >>>> rxhash set, and this function is what's killing performance. Let me share >>>> the details: >>>> >>> I think I figured this out. The upstream source port selection algorithm is >>> exploding flows >>> in the fast path. Here are iperf runs with both and subsequent "ovs-dpctl >>> dump-flows" >>> commands for comparison. The first one is with the upstream version, the >>> second is >>> with the one in my patch. Note that I just piped "ovs-dpctl dump-flows" >>> into wc to >>> summarize the flow count. >>> >>> Upstream verison: >>> [root@linux-br ~]# iperf -c 10.1.2.14 && ovs-dpctl dump-flows | wc >> >> >> Figured this out, fixing it now, will repost the patch with only this change >> soon. >> > > So after looking at this, the upstream source port selection function will > cause an explosion > of fast path flows due to an ever changing skbuff->rxhash. By using the > flow->hash, we > don't see this problem. Jesse, any comments on this particular issue? I think > using the > upstream function will allow for greater spreading across links depending on > the hashing > algorithm used on upstream switches, but will cause this flow explosion on > the host itself.
Generally speaking, the OVS flow extraction pulls out more fields than are usually used by skb_get_rxhash() so I'm surprised that it would have this effect (of course, neither is supposed to be so fine grained that it breaks down a single 'real' flow). It sounds to me like there is a bug that is pulling in random data that's not supposed to be part of the flow if it changes on a per packet basis. Do you know if you are getting a value from skb_get_rxhash() or is it falling back to the Ethernet headers? _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
