[ovs-dev] 答复: 答复: [PATCH] userspace: fix bad UDP performance issue of?veth

Flavio Leitner fbl at sysclose.org
Wed Sep 2 17:31:45 UTC 2020


On Mon, Aug 31, 2020 at 12:38:16AM +0000, Yi Yang (杨燚)-云服务集团 wrote:
> Flavio, per my test, it also improved TCP performance, you can use
> run-iperf.sh script  I sent to have a try. Actually, iperf3 did
> the same thing by using -w option. 

I believe that the results improve with lab tests on a controlled
environment. The kernel auto-tune buffer and the backlogging happens
when the system is busy with something else and you have multiple
devices and TCP streams going on.  For instance, the bufferbloat
problem as Aaron already mentioned.

So, I agree with Aaron that this needs a config knob for cases where
using the maximum is not a good idea. For instance, I know that some
software solutions out there recommends to pump those defaults to
huge numbers, which might be ok for that solution, but it may cause
OVS issues under load.

Does that make sense?

fbl

> 
> -----邮件原件-----
> 发件人: Flavio Leitner [mailto:fbl at sysclose.org] 
> 发送时间: 2020年8月27日 21:28
> 收件人: Yi Yang (杨燚)-云服务集团 <yangyi01 at inspur.com>
> 抄送: aconole at redhat.com; yang_y_yi at 163.com; ovs-dev at openvswitch.org; i.maximets at ovn.org
> 主题: Re: [ovs-dev] 答复: [PATCH] userspace: fix bad UDP performance issue of?veth
> 
> 
> Hi,
> 
> 
> On Wed, Aug 26, 2020 at 12:47:43AM +0000, Yi Yang (杨燚)-云服务集团 wrote:
> > Aaron, thank for your comments, actually final value depends on 
> > /proc/sys/net/core/rmem_max and /proc/sys/net/core/wmem_max, so it is 
> > still configurable. setsockopt(...) will set it to minimum one among 
> > of
> > 1073741823 and w/rmem_max.
> > 
> > -----邮件原件-----
> > 发件人: dev [mailto:ovs-dev-bounces at openvswitch.org] 代表 Aaron Conole
> > 发送时间: 2020年8月25日 23:26
> > 收件人: yang_y_yi at 163.com
> > 抄送: ovs-dev at openvswitch.org; i.maximets at ovn.org; fbl at sysclose.org
> > 主题: Re: [ovs-dev] [PATCH] userspace: fix bad UDP performance issue of 
> > veth
> > 
> > yang_y_yi at 163.com writes:
> > 
> > > From: Yi Yang <yangyi01 at inspur.com>
> > >
> > > iperf3 UDP performance of veth to veth case is very very bad because 
> > > of too many packet loss, the root cause is rmem_default and 
> > > wmem_default are just 212992, but iperf3 UDP test used 8K UDP size 
> > > which resulted in many UDP fragment in case that MTU size is 1500, 
> > > one 8K UDP send would enqueue 6 UDP fragments to socket receive 
> > > queue, the default small socket buffer size can't cache so many 
> > > packets that many packets are lost.
> > >
> > > This commit fixed packet loss issue, it set socket receive and send 
> > > buffer to maximum possible value, therefore there will not be packet 
> > > loss forever, this also helps improve TCP performance because of no 
> > > retransmit.
> > >
> > > By the way, big socket buffer doesn't mean it will allocate big 
> > > buffer on creating socket, actually it won't alocate any extra 
> > > buffer compared to default socket buffer size, it just means more 
> > > skbuffs can be enqueued to socket receive queue and send queue, 
> > > therefore there will not be packet loss.
> > >
> > > The below is for your reference.
> > >
> > > The result before apply this commit
> > > ===================================
> > > $ ip netns exec ns02 iperf3 -t 5 -i 1 -u -b 100M -c 10.15.2.6 
> > > --get-server-output -A 5 Connecting to host 10.15.2.6, port 5201 [  
> > > 4] local 10.15.2.2 port 59053 connected to 10.15.2.6 port 5201
> > > [ ID] Interval           Transfer     Bandwidth       Total Datagrams
> > > [  4]   0.00-1.00   sec  10.8 MBytes  90.3 Mbits/sec  1378
> > > [  4]   1.00-2.00   sec  11.9 MBytes   100 Mbits/sec  1526
> > > [  4]   2.00-3.00   sec  11.9 MBytes   100 Mbits/sec  1526
> > > [  4]   3.00-4.00   sec  11.9 MBytes   100 Mbits/sec  1526
> > > [  4]   4.00-5.00   sec  11.9 MBytes   100 Mbits/sec  1526
> > > - - - - - - - - - - - - - - - - - - - - - - - - -
> > > [ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
> > > [  4]   0.00-5.00   sec  58.5 MBytes  98.1 Mbits/sec  0.047 ms  357/531 (67%)
> > > [  4] Sent 531 datagrams
> > >
> > > Server output:
> > > -----------------------------------------------------------
> > > Accepted connection from 10.15.2.2, port 60314 [  5] local 10.15.2.6 
> > > port 5201 connected to 10.15.2.2 port 59053
> > > [ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
> > > [  5]   0.00-1.00   sec  1.36 MBytes  11.4 Mbits/sec  0.047 ms  357/531 (67%)
> > > [  5]   1.00-2.00   sec  0.00 Bytes  0.00 bits/sec  0.047 ms  0/0 (-nan%)
> > > [  5]   2.00-3.00   sec  0.00 Bytes  0.00 bits/sec  0.047 ms  0/0 (-nan%)
> > > [  5]   3.00-4.00   sec  0.00 Bytes  0.00 bits/sec  0.047 ms  0/0 (-nan%)
> > > [  5]   4.00-5.00   sec  0.00 Bytes  0.00 bits/sec  0.047 ms  0/0 (-nan%)
> > >
> > > iperf Done.
> > >
> > > The result after apply this commit
> > > ===================================
> > > $ sudo ip netns exec ns02 iperf3 -t 5 -i 1 -u -b 4G -c 10.15.2.6 
> > > --get-server-output -A 5 Connecting to host 10.15.2.6, port 5201 [  
> > > 4] local 10.15.2.2 port 48547 connected to 10.15.2.6 port 5201
> > > [ ID] Interval           Transfer     Bandwidth       Total Datagrams
> > > [  4]   0.00-1.00   sec   440 MBytes  3.69 Gbits/sec  56276
> > > [  4]   1.00-2.00   sec   481 MBytes  4.04 Gbits/sec  61579
> > > [  4]   2.00-3.00   sec   474 MBytes  3.98 Gbits/sec  60678
> > > [  4]   3.00-4.00   sec   480 MBytes  4.03 Gbits/sec  61452
> > > [  4]   4.00-5.00   sec   480 MBytes  4.03 Gbits/sec  61441
> > > - - - - - - - - - - - - - - - - - - - - - - - - -
> > > [ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
> > > [  4]   0.00-5.00   sec  2.30 GBytes  3.95 Gbits/sec  0.024 ms  0/301426 (0%)
> > > [  4] Sent 301426 datagrams
> > >
> > > Server output:
> > > -----------------------------------------------------------
> > > Accepted connection from 10.15.2.2, port 60320 [  5] local 10.15.2.6 
> > > port 5201 connected to 10.15.2.2 port 48547
> > > [ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
> > > [  5]   0.00-1.00   sec   209 MBytes  1.75 Gbits/sec  0.021 ms  0/26704 (0%)
> > > [  5]   1.00-2.00   sec   258 MBytes  2.16 Gbits/sec  0.025 ms  0/32967 (0%)
> > > [  5]   2.00-3.00   sec   258 MBytes  2.16 Gbits/sec  0.022 ms  0/32987 (0%)
> > > [  5]   3.00-4.00   sec   257 MBytes  2.16 Gbits/sec  0.023 ms  0/32954 (0%)
> > > [  5]   4.00-5.00   sec   257 MBytes  2.16 Gbits/sec  0.021 ms  0/32937 (0%)
> > > [  5]   5.00-6.00   sec   255 MBytes  2.14 Gbits/sec  0.026 ms  0/32685 (0%)
> > > [  5]   6.00-7.00   sec   254 MBytes  2.13 Gbits/sec  0.025 ms  0/32453 (0%)
> > > [  5]   7.00-8.00   sec   255 MBytes  2.14 Gbits/sec  0.026 ms  0/32679 (0%)
> > > [  5]   8.00-9.00   sec   255 MBytes  2.14 Gbits/sec  0.022 ms  0/32669 (0%)
> > >
> > > iperf Done.
> > >
> > > Signed-off-by: Yi Yang <yangyi01 at inspur.com>
> > > ---
> > 
> > I think we should make it configurable.  Each RXQ will potentially allow a huge number of skbuffs to be enqueued after this.  That might, ironically, lead to worse performance (since there could be some kind of buffer bloat effect at higher rmem values as documented at https://serverfault.com/questions/410230/higher-rmem-max-value-leading-to-more-packet-loss).
> > 
> > I think it should be a decision that the operator can take.  Currently, they could modify it anyway via procfs, so we shouldn't break that.
> > Instead, I think there could be a config knob (or maybe reuse the
> > 'n_{r,t}xq_desc'?) that when set would be used, and otherwise could just be from default.
> 
> If my memory serves me right, calling setsockopt(SO_RCVBUF) disables kernel's auto-tune buffer which very often hurts TCP performance, especially under load. 
> 
> --
> fbl
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-- 
fbl


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