Re: [dpdk-dev] DPDK testpmd forwarding performace degradation

["De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>]

Hi Alexander,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Alexander Belyakov
> Sent: Monday, January 26, 2015 10:18 AM
> To: dev@dpdk.org
> Subject: [dpdk-dev] DPDK testpmd forwarding performace degradation
> 
> Hello,
> 
> recently I have found a case of significant performance degradation for our
> application (built on top of DPDK, of course). Surprisingly, similar issue
> is easily reproduced with default testpmd.
> 
> To show the case we need simple IPv4 UDP flood with variable UDP payload
> size. Saying "packet length" below I mean: Eth header length (14 bytes) +
> IPv4 header length (20 bytes) + UPD header length (8 bytes) + UDP payload
> length (variable) + CRC (4 bytes). Source IP addresses and ports are selected
> randomly for each packet.
> 
> I have used DPDK with revisions 1.6.0r2 and 1.7.1. Both show the same issue.
> 
> Follow "Quick start" guide (http://dpdk.org/doc/quick-start) to build and
> run testpmd. Enable testpmd forwarding ("start" command).
> 
> Table below shows measured forwarding performance depending on packet
> length:
> 
> No. -- UDP payload length (bytes) -- Packet length (bytes) -- Forwarding
> performance (Mpps) -- Expected theoretical performance (Mpps)
> 
> 1. 0 -- 64 -- 14.8 -- 14.88
> 2. 34 -- 80 -- 12.4 -- 12.5
> 3. 35 -- 81 -- 6.2 -- 12.38 (!)
> 4. 40 -- 86 -- 6.6 -- 11.79
> 5. 49 -- 95 -- 7.6 -- 10.87
> 6. 50 -- 96 -- 10.7 -- 10.78 (!)
> 7. 60 -- 106 -- 9.4 -- 9.92
> 
> At line number 3 we have added 1 byte of UDP payload (comparing to
> previous
> line) and got forwarding performance halved! 6.2 Mpps against 12.38 Mpps
> of
> expected theoretical maximum for this packet size.
> 
> That is the issue.
> 
> Significant performance degradation exists up to 50 bytes of UDP payload
> (96 bytes packet length), where it jumps back to theoretical maximum.
> 
> What is happening between 80 and 96 bytes packet length?
> 
> This issue is stable and 100% reproducible. At this point I am not sure if
> it is DPDK or NIC issue. These tests have been performed on Intel(R) Eth
> Svr Bypass Adapter X520-LR2 (X520LR2BP).
> 
> Is anyone aware of such strange behavior?

I cannot reproduce the issue using two ports on two different 82599EB NICs, using 1.7.1 and 1.8.0.
I always get either same or better linerate as I increase the packet size.
Actually, have you tried using 1.8.0? 

Pablo
> 
> Regards,
> Alexander Belyakov