[dpdk-dev] Rx_missed_errors drops with larger packet size

[Bruce Richardson]

On Fri, May 20, 2016 at 02:09:02AM -0700, SwamZ wrote:
> Hi,
> 
> 
> While doing performance testing with larger packet size (like 4000 bytes),
> we are seeing rx_missed_errors on the interface. This issue is not seen
> with packet size less than 2000. There were questions asked in this forum
> on rx_missed_error, but there was not any conclusion. Please let me know
> what could be the reason for these drops.
> 
> 
> I tried the following without any luck:
> 
> 1) Tried different burst size like 16, 32 an 64
> 
> 2) Tried different number of the rx descriptors like 512, 1024, 2048 and
> 4096.
> 
> 
> Setup and testing details:
> 
> CPU Speed : 2.6 GHz
> 
> NIC           : 82599ES 10-Gigabit
> 
> IO Virtualization: SR-IOV
> 
> IO and packet processing cores are in the same NUMA.
> 
> Packet size : 4000 bytes
> 
> Traffic rate: 80 % line rate. If the traffic rate is < ~80% then drops are
> not seen.
> 
> Application: This is a sample application developed using L3fwd example app.
> 
> DPDK version: 1.7

Hi,

Couple of follow up questions:
1. Can you confirm that you are using the standard ~2k buffer size, implying
that you are using the slower scattered RX/TX code paths for the 4k packet size
case? If so, can you try increasing your buffer size to 5k and see what happens?
2. Does the issue still occur on the latest DPDK 16.04 release, or on the latest
code on dpdk.org. Release 1.7 is very old at this stage.

Regards,
/Bruce