[dpdk-dev] Rx-errors with testpmd (only 75% line rate)

[Dmitry Vyal]

On 01/28/2014 12:00 AM, Michael Quicquaro wrote:
> Dmitry,
> I cannot thank you enough for this information.  This too was my main 
> problem.  I put a "small" unmeasured delay before the call to 
> rte_eth_rx_burst() and suddenly it starts returning bursts of 512 
> packets vs. 4!!
> Best Regards,
> Mike
>

Thanks for confirming my guesses! By the way, make sure the number of 
packets you receive in a single burst is less than configured queue 
size. Or you will lose packets too. Maybe your "small" delay in not so 
small :) For my own purposes I use a delay of about 150usecs.

P.S. I wonder why this issue is not mentioned in documentation. Is it 
evident for everyone doing network programming?


>
> On Wed, Jan 22, 2014 at 9:52 AM, Dmitry Vyal <dmitryvyal at gmail.com 
> <mailto:dmitryvyal at gmail.com>> wrote:
>
>     Hello MIchael,
>
>     I suggest you to check average burst sizes on receive queues.
>     Looks like I stumbled upon a similar issue several times. If you
>     are calling rte_eth_rx_burst too frequently, NIC begins losing
>     packets no matter how many CPU horse power you have (more you
>     have, more it loses, actually). In my case this situation occured
>     when average burst size is less than 20 packets or so. I'm not
>     sure what's the reason for this behavior, but I observed it on
>     several applications on Intel 82599 10Gb cards.
>
>     Regards, Dmitry
>
>
>
>     On 01/09/2014 11:28 PM, Michael Quicquaro wrote:
>
>         Hello,
>         My hardware is a Dell PowerEdge R820:
>         4x Intel Xeon E5-4620 2.20GHz 8 core
>         16GB RDIMM 1333 MHz Dual Rank, x4 - Quantity 16
>         Intel X520 DP 10Gb DA/SFP+
>
>         So in summary 32 cores @ 2.20GHz and 256GB RAM
>
>         ... plenty of horsepower.
>
>         I've reserved 16 1GB Hugepages
>
>         I am configuring only one interface and using testpmd in
>         rx_only mode to
>         first see if I can receive at line rate.
>
>         I am generating traffic on a different system which is running
>         the netmap
>         pkt-gen program - generating 64 byte packets at close to line
>         rate.
>
>         I am only able to receive approx. 75% of line rate and I see
>         the Rx-errors
>         in the port stats going up proportionally.
>         I have verified that all receive queues are being used, but
>         strangely
>         enough, it doesn't matter how many queues more than 2 that I
>         use, the
>         throughput is the same.  I have verified with 'mpstat -P ALL'
>         that all
>         specified cores are used.  The utilization of each core is
>         only roughly 25%.
>
>         Here is my command line:
>         testpmd -c 0xffffffff -n 4 -- --nb-ports=1 --coremask=0xfffffffe
>         --nb-cores=8 --rxd=2048 --txd=2048 --mbcache=512 --burst=512
>         --rxq=8
>         --txq=8 --interactive
>
>         What can I do to trace down this problem?  It seems very
>         similar to a
>         thread on this list back in May titled "Best example for showing
>         throughput?" where no resolution was ever mentioned in the thread.
>
>         Thanks for any help.
>         - Michael
>
>
>