[dpdk-users] Query on handling packets

Wiles, Keith keith.wiles at intel.com
Tue Feb 5 15:12:43 CET 2019



> On Feb 5, 2019, at 8:00 AM, Harsh Patel <thadodaharsh10 at gmail.com> wrote:
> 
> Hi, 
> One of the mistake was as following. ns-3 frees the packet buffer just as it writes to the socket and thus we thought that we should also do the same. But dpdk while writing places the packet buffer to the tx descriptor ring and perform the transmission after that on its own. And we were freeing early so sometimes the packets were lost i.e. freed before transmission. 
> 
> Another thing was that as you suggested earlier we compiled the whole ns-3 in optimized mode. That improved the performance. 
> 
> These 2 things combined got us the desired results. 

Excellent thanks
> 
> Regards, 
> Harsh & Hrishikesh 
> 
> On Tue, Feb 5, 2019, 18:33 Wiles, Keith <keith.wiles at intel.com> wrote:
> 
> 
> > On Feb 5, 2019, at 12:37 AM, Harsh Patel <thadodaharsh10 at gmail.com> wrote:
> > 
> > Hi, 
> > 
> > We would like to inform you that our code is working as expected and we are able to obtain 95-98 Mbps data rate for a 100Mbps application rate. We are now working on the testing of the code. Thanks a lot, especially to Keith for all the help you provided.
> > 
> > We have 2 main queries :-
> > 1) We wanted to calculate Backlog at the NIC Tx Descriptors but were not able to find anything in the documentation. Can you help us in how to calculate the backlog?
> > 2) We searched on how to use Byte Queue Limit (BQL) on the NIC queue but couldn't find anything like that in DPDK. Does DPDK support BQL? If so, can you help us on how to use it for our project?
> 
> what was the last set of problems if I may ask?
> > 
> > Thanks & Regards
> > Harsh & Hrishikesh
> > 
> > On Thu, 31 Jan 2019 at 22:28, Wiles, Keith <keith.wiles at intel.com> wrote:
> > 
> > 
> > Sent from my iPhone
> > 
> > On Jan 30, 2019, at 5:36 PM, Harsh Patel <thadodaharsh10 at gmail.com> wrote:
> > 
> >> Hello, 
> >> 
> >> This mail is to inform you that the integration of DPDK is working with ns-3 on a basic level. The model is running. 
> >> For UDP traffic we are getting throughput same or better than raw socket. (Around 100Mbps)
> >> But unfortunately for TCP, there are burst packet losses due to which the throughput is drastically affected after some point of time. The bandwidth of the link used was 100Mbps. 
> >> We have obtained cwnd and ssthresh graphs which show that once the flow gets out from Slow Start mode, there are so many packet losses that the congestion window & the slow start threshold is not able to go above 4-5 packets. 
> > 
> > Can you determine where the packets are being dropped?
> >> We have attached the graphs with this mail.
> >> 
> > 
> > I do not see the graphs attached but that’s OK. 
> >> We would like to know if there is any reason to this or how can we fix this. 
> > 
> > I think we have to find out where the packets are being dropped this is the only reason for the case to your referring to. 
> >> 
> >> Thanks & Regards
> >> Harsh & Hrishikesh
> >> 
> >> On Wed, 16 Jan 2019 at 19:25, Harsh Patel <thadodaharsh10 at gmail.com> wrote:
> >> Hi
> >> 
> >> We were able to optimise the DPDK version. There were couple of things we needed to do.
> >> 
> >> We were using tx timeout as 1s/2048, which we found out to be very less. Then we increased the timeout, but we were getting lot of retransmissions.
> >> 
> >> So we removed the timeout and sent single packet as soon as we get it. This increased the throughput.
> >> 
> >> Then we used DPDK feature to launch function on core, and gave a dedicated core for Rx. This increased the throughput further.
> >> 
> >> The code is working really well for low bandwidth (<~50Mbps) and is outperforming raw socket version.
> >> But for high bandwidth, we are getting packet length mismatches for some reason. We are investigating it.
> >> 
> >> We really thank you for the suggestions given by you and also for keeping the patience for last couple of months. 
> >> 
> >> Thank you
> >> 
> >> Regards, 
> >> Harsh & Hrishikesh 
> >> 
> >> On Fri, Jan 4, 2019, 11:27 Harsh Patel <thadodaharsh10 at gmail.com> wrote:
> >> Yes that would be helpful. 
> >> It'd be ok for now to use the same dpdk version to overcome the build issues. 
> >> We will look into updating the code for latest versions once we get past this problem. 
> >> 
> >> Thank you very much. 
> >> 
> >> Regards, 
> >> Harsh & Hrishikesh
> >> 
> >> On Fri, Jan 4, 2019, 04:13 Wiles, Keith <keith.wiles at intel.com> wrote:
> >> 
> >> 
> >> > On Jan 3, 2019, at 12:12 PM, Harsh Patel <thadodaharsh10 at gmail.com> wrote:
> >> > 
> >> > Hi
> >> > 
> >> > We applied your suggestion of removing the `IsLinkUp()` call. But the performace is even worse. We could only get around 340kbits/s.
> >> > 
> >> > The Top Hotspots are:
> >> > 
> >> > Function    Module    CPU Time
> >> > eth_em_recv_pkts    librte_pmd_e1000.so    15.106s
> >> > rte_delay_us_block    librte_eal.so.6.1    7.372s
> >> > ns3::DpdkNetDevice::Read    libns3.28.1-fd-net-device-debug.so    5.080s
> >> > rte_eth_rx_burst    libns3.28.1-fd-net-device-debug.so    3.558s
> >> > ns3::DpdkNetDeviceReader::DoRead    libns3.28.1-fd-net-device-debug.so    3.364s
> >> > [Others]        4.760s
> >> 
> >> Performance reduced by removing that link status check, that is weird.
> >> > 
> >> > Upon checking the callers of `rte_delay_us_block`, we got to know that most of the time (92%) spent in this function is during initialization.
> >> > This does not waste our processing time during communication. So, it's a good start to our optimization.
> >> > 
> >> > Callers    CPU Time: Total    CPU Time: Self
> >> > rte_delay_us_block    100.0%    7.372s
> >> >   e1000_enable_ulp_lpt_lp    92.3%    6.804s
> >> >   e1000_write_phy_reg_mdic    1.8%    0.136s
> >> >   e1000_reset_hw_ich8lan    1.7%    0.128s
> >> >   e1000_read_phy_reg_mdic    1.4%    0.104s
> >> >   eth_em_link_update    1.4%    0.100s
> >> >   e1000_get_cfg_done_generic    0.7%    0.052s
> >> >   e1000_post_phy_reset_ich8lan.part.18    0.7%    0.048s
> >> 
> >> I guess you are having vTune start your application and that is why you have init time items in your log. I normally start my application and then attach vtune to the application. One of the options in configuration of vtune for that project is to attach to the application. Maybe it would help hear.
> >> 
> >> Looking at the data you provided it was ok. The problem is it would not load the source files as I did not have the same build or executable. I tried to build the code, but it failed to build and I did not go further. I guess I would need to see the full source tree and the executable you used to really look at the problem. I have limited time, but I can try if you like. 
> >> > 
> >> > 
> >> > Effective CPU Utilization:    21.4% (0.856 out of 4)
> >> > 
> >> > Here is the link to vtune profiling results. https://drive.google.com/open?id=1M6g2iRZq2JGPoDVPwZCxWBo7qzUhvWi5
> >> > 
> >> > Thank you
> >> > 
> >> > Regards
> >> > 
> >> > On Sun, Dec 30, 2018, 06:00 Wiles, Keith <keith.wiles at intel.com> wrote:
> >> > 
> >> > 
> >> > > On Dec 29, 2018, at 4:03 PM, Harsh Patel <thadodaharsh10 at gmail.com> wrote:
> >> > > 
> >> > > Hello,
> >> > > As suggested, we tried profiling the application using Intel VTune Amplifier. We aren't sure how to use these results, so we are attaching them to this email.
> >> > > 
> >> > > The things we understood were 'Top Hotspots' and 'Effective CPU utilization'. Following are some of our understandings:
> >> > > 
> >> > > Top Hotspots
> >> > > 
> >> > > Function        Module  CPU Time
> >> > > rte_delay_us_block      librte_eal.so.6.1       15.042s
> >> > > eth_em_recv_pkts        librte_pmd_e1000.so     9.544s
> >> > > ns3::DpdkNetDevice::Read        libns3.28.1-fd-net-device-debug.so      3.522s
> >> > > ns3::DpdkNetDeviceReader::DoRead        libns3.28.1-fd-net-device-debug.so      2.470s
> >> > > rte_eth_rx_burst        libns3.28.1-fd-net-device-debug.so      2.456s
> >> > > [Others]                6.656s
> >> > > 
> >> > > We knew about other methods except `rte_delay_us_block`. So we investigated the callers of this method:
> >> > > 
> >> > > Callers Effective Time  Spin Time       Overhead Time   Effective Time  Spin Time       Overhead Time   Wait Time: Total        Wait Time: Self
> >> > > e1000_enable_ulp_lpt_lp 45.6%   0.0%    0.0%    6.860s  0usec   0usec
> >> > > e1000_write_phy_reg_mdic        32.7%   0.0%    0.0%    4.916s  0usec   0usec
> >> > > e1000_read_phy_reg_mdic 19.4%   0.0%    0.0%    2.922s  0usec   0usec
> >> > > e1000_reset_hw_ich8lan  1.0%    0.0%    0.0%    0.143s  0usec   0usec
> >> > > eth_em_link_update      0.7%    0.0%    0.0%    0.100s  0usec   0usec
> >> > > e1000_post_phy_reset_ich8lan.part.18    0.4%    0.0%    0.0%    0.064s  0usec   0usec
> >> > > e1000_get_cfg_done_generic      0.2%    0.0%    0.0%    0.037s  0usec   0usec
> >> > > 
> >> > > We lack sufficient knowledge to investigate more than this.
> >> > > 
> >> > > Effective CPU utilization
> >> > > 
> >> > > Interestingly, the effective CPU utilization was 20.8% (0.832 out of 4 logical CPUs). We thought this is less. So we compared this with the raw-socket version of the code, which was even less, 8.0% (0.318 out of 4 logical CPUs), and even then it is performing way better.
> >> > > 
> >> > > It would be helpful if you give us insights on how to use these results or point us to some resources to do so. 
> >> > > 
> >> > > Thank you 
> >> > > 
> >> > 
> >> > BTW, I was able to build ns3 with DPDK 18.11 it required a couple changes in the DPDK init code in ns3 plus one hack in rte_mbuf.h file.
> >> > 
> >> > I did have a problem including rte_mbuf.h file into your code. It appears the g++ compiler did not like referencing the struct rte_mbuf_sched inside the rte_mbuf structure. The rte_mbuf_sched was inside the big union as a hack I moved the struct outside of the rte_mbuf structure and replaced the struct in the union with ’struct rte_mbuf_sched sched;', but I am guessing you are missing some compiler options in your build system as DPDK builds just fine without that hack.
> >> > 
> >> > The next place was the rxmode and the txq_flags. The rxmode structure has changed and I commented out the inits in ns3 and then commented out the txq_flags init code as these are now the defaults.
> >> > 
> >> > Regards,
> >> > Keith
> >> > 
> >> 
> >> Regards,
> >> Keith
> >> 
> >> <Ssthresh.png>
> >> <Cwnd.png>
> 
> Regards,
> Keith
> 

Regards,
Keith



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