On 2/13/20 12:48 PM, Flavio Leitner wrote:
> On Thu, Feb 13, 2020 at 09:18:38AM +0000, Yi Yang (杨燚)-云服务集团 wrote:
>> Hi, all
>> We find ovs has serious performance issue, we only launch one VM in one 
>> compute, and do iperf small udp pps performance test between these two VMs, 
>> we can see about 180000 pps (packets per second, -l 16), but
>> 1) if we add 100 veth ports in br-int bridge, respectively, then the pps 
>> performance will be about 50000 pps.
>> 2) If we launch one more VM in every compute node, but don’t run any 
>> workload, the pps performance will be about 90000 pps. (note, no above veth 
>> ports in this test)
>> 3) If we launch two more VMs in every compute node (totally 3 VMs every 
>> compute nodes), but don’t run any workload , the pps performance will be 
>> about 50000 pps (note, no above veth ports in this test)
>> Anybody can help explain why it is so? Is there any known way to optimized 
>> this? I really think ovs performance is bad (we can draw such conclusion 
>> from our test result at least), I don’t want to defame ovs ☺
>> BTW, we used ovs kernel datapath and vhost, we can see every port has a 
>> vhost kernel thread, it is running with 100% cpu utilization if we run iperf 
>> in VM, bu for those idle VMs, the corresponding vhost still has about 30% 
>> cpu utilization, I don’t understand why.
>> In addition, we find udp performance is also very bad for small UDP packet 
>> for physical NIC. But it can reach 260000 pps for –l 80 which enough covers 
>> vxlan header (8 bytes) + inner eth header (14) + ipudp header (28) + 16 = 
>> 66, if we consider performance overhead ovs bridge introduces, pps 
>> performance between VMs should be able to reach 200000 pps at least, other 
>> VMs and ports shouldn’t have so big hurt against it because they are idle, 
>> no any workload there.
> What do you have in the flow table?  It sounds like the traffic is
> being broadcast to all ports. Check the FDB to see if OvS is
> learning the mac addresses.
> It's been a while since I don't run performance tests with kernel
> datapath, but it should be no different than Linux bridge with 
> just action NORMAL in the flow table.

I agree that if your performance heavily depends on the number of
ports than you're most likely just flooding all the packets to
all the ports.  Since you're using UDP traffic, please, be sure
that you're sending some packets in backward direction, so OVS
and all other switches (if any) will learn/not forget to which
port packets should be sent.  Also, check if your IP addresses
are correct.  If for some reason it's not possible for OVS to
learn MAC addresses correctly, avoid using action:NORMAL.

Best regards, Ilya Maximets.
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