[dpdk-users] Query on handling packets

Harsh Patel thadodaharsh10 at gmail.com
Tue Feb 5 15:33:14 CET 2019


Cool. Thanks a lot. We'll do that.

On Tue, Feb 5, 2019, 19:57 Wiles, Keith <keith.wiles at intel.com> wrote:

>
>
> > On Feb 5, 2019, at 8:22 AM, Harsh Patel <thadodaharsh10 at gmail.com>
> wrote:
> >
> > Can you help us with those questions we asked you? We need them as
> parameters for our testing.
>
> i would love to but i do not know much about what you are asking, sorry.
>
> i hope someone else steps in, maybe the pmd maintainer could help. look in
> the maintainers file and message him directly.
> >
> > Thanks,
> > Harsh & Hrishikesh
> >
> > On Tue, Feb 5, 2019, 19:42 Wiles, Keith <keith.wiles at intel.com> wrote:
> >
> >
> > > 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
> >
>
> Regards,
> Keith
>
>


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