On 2/13/20 2:52 PM, Yi Yang (杨燚)-云服务集团 wrote:
> Thanks Ilya, iperf3 udp should be single direction, source IP address and
> destination IP address are two VMs' IP, udp bandwidth will be 0 if they are
> wrong, but obviously UDP loss rate is 0, so it isn't the case you're saying,
> do we have way to disable MAC learning or MAC broadcast?
NORMAL action acts like an L2 learning switch. If you don't
want to use MAC learning, remove flow with NORMAL action and
add direct forwarding flow like output:<desired port>. But
I don't think that you want to do that in OpenStack setup.
>
> Is NORMAL action or MAC learning slow path process? If so, ovs-vswitchd
> daemon should have high cpu utilization.
It's not a slow path, so there will be no cpu usage by ovs-vswitchd
userspace process. To confirm that you're flooding packets, you
may dump installed datapath flows with the following command:
ovs-appctl dpctl/dump-flows
In case of flood, you will see datapath flow with big number of
output ports like this:
<...> actions:<port #1>,<port #2>,<port #3>...
>
> -----邮件原件-----
> 发件人: Ilya Maximets [mailto:i.maxim...@ovn.org]
> 发送时间: 2020年2月13日 21:23
> 收件人: Flavio Leitner <f...@sysclose.org>; Yi Yang (杨燚)-云服务集团
> <yangy...@inspur.com>
> 抄送: ovs-disc...@openvswitch.org; ovs-dev@openvswitch.org; Ilya Maximets
> <i.maxim...@ovn.org>
> 主题: Re: [ovs-dev] OVS performance issue: why small udp packet pps performance
> between VMs is highly related with number of ovs ports and number of VMs?
>
> 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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