[dpdk-users] Packet losses using DPDK

[Wiles, Keith]

> On May 12, 2017, at 10:45 AM, dfernandes at toulouse.viveris.com wrote:
> 
> Hi !
> 
> I am working with MoonGen which is a fully scriptable packet generator build on DPDK.
> (→ https://github.com/emmericp/MoonGen)
> 
> The system on which I perform tests has the following characteristics :
> 
> CPU : Intel Core i3-⁠⁠6100 (3.70 GHz, 2 cores, 2 threads/⁠⁠core)
> NIC : X540-⁠⁠AT2 with 2x10Gbe ports
> OS : Linux Ubuntu Server 16.04 (kernel 4.4)
> 
> I coded a MoonGen script which requests DPDK to transmit packets from one physical port and to receive them at the second physical port. The 2 physical ports are directly connected with an RJ-45 cat6 cable.
> 
> The issue is that I perform the same test with exactly the same script and the same parameters several times and the results show a random behavior. For most of the tests there is no losses but for some of them I observe packet losses. The percentage of lost packets is very variable. It happens even when the packet rate is very low.
> 
> Some examples of random failed tests :
> 
> # 1,000,000 packets sent (packets size = 124 bytes, rate = 76 Mbps) → 10170 lost packets
> 
> # 3,000,000 packets sent (packets size = 450 bytes, rate = 460 Mbps) → ALL packets lost
> 
> 
> I tested the following system modifications without success :
> 
> # BIOS parameters :
> 
>    Hyperthreading : enable (because the machine has only 2 cores)
>    Multi-⁠⁠⁠processor : enable
>    Virtualization Technology (VTx) : disable
>    Virtualization Technology for Directed I/⁠⁠⁠O (VTd) : disable
>    Allow PCIe/⁠⁠⁠PCI SERR# Interrupt (=PCIe System Errors) : disable
>    NUMA unavailable
> 
> # use of isolcpus in order to isolate the cores which are in charge of transmission and reception
> 
> # hugepages size = 1048576 kB
> 
> # size of buffer descriptors : tried with Tx = 512 descriptors and Rx = 128 descriptors and also with  Tx = 4096 descriptors and Rx = 4096  descriptors
> 
> # Tested with 2 different X540-⁠⁠T2 NICs units
> 
> # I tested all with a Dell FC430 which has a CPU Intel Xeon E5-2660 v3 @ 2.6GHz with 10 Cores and 2threads/Core (tested with and without hyper-threading)
>    → same results and even worse
> 
> 
> Remark concerning the NIC stats :
>     I used the rte_eth_stats struct in order to get more information about the losses and I observed that in some cases, when there is packet losses,  ierrors value is > 0 and also ierrors + imissed + ipackets < opackets. In other cases I get ierrors = 0 and  imissed + ipackets = opackets which has more sense.
> 
> What could be the origin of that erroneous packets counting?
> 
> Do you have any explanation about that behaviour ?

Not knowing MoonGen at all other then a brief look at the source I may not be much help, but I have a few ideas to help locate the problem.

Try using testpmd in tx-only mode or try Pktgen to see if you get the same problem. I hope this would narrow down the problem to a specific area. As we know DPDK works if correctly coded and testpmd/pktgen work.

> 
> Thanks in advance.
> 
> David

Regards,
Keith