Low TX rate with 512B frames

[alialnu]

Starting from TRex v2.80, there is a ~50% drop in TX rate with 512B frames.

The issue can be reproduced with stl/bench.py.

To reproduce, start TRex:
$ ./t-rex-64 -i -c 14

Then start traffic and monitor stats:
> start -p 0 1 -m 100% -f stl/bench.py -t size=512,vm=cached

This was caused by dbb64b2, and the last good version is v2.79.

NIC: ConnectX-5.
Reproduces with multiple versions of MLNX_OFED (4.6-1.0.1.1, 5.2-2.2.0.0 and 5.3-1.0.0.1).

[hhaim]

@alialnu This is a mlx5 driver/ofed issue. trex code is the same. could you check with latest DPDK version v2.89 and latest ofed?

[alialnu]

@alialnu This is a mlx5 driver/ofed issue. trex code is the same. could you check with latest DPDK version v2.89 and latest ofed?

I can also reproduce with v2.89.

[hhaim]

@alialnu it means that this is a dpdk mlx5 driver issue. try to figure out what was change betwean the DPDK. You can try to to git bisect to find the driver change that intruduce this.

[aleks-kozyrev]

@hhaim could you please try adding "dpdk_devargs : ['txq_inline_min=1','txq_inline_max=700']" to your trex_cfg.yaml file.
This should restore the performance for 512 bytes traffic generation.

[alialnu]

@hhaim could you please try adding "dpdk_devargs : ['txq_inline_min=1','txq_inline_max=700']" to your trex_cfg.yaml file.
This should restore the performance for 512 bytes traffic generation.

Thanks for the suggestion @aleks-kozyrev. I'll try it Do you have an example of how to add this modification to the file?

[alialnu]

@hhaim could you please try adding "dpdk_devargs : ['txq_inline_min=1','txq_inline_max=700']" to your trex_cfg.yaml file.
This should restore the performance for 512 bytes traffic generation.

Thanks for the suggestion @aleks-kozyrev. I'll try it Do you have an example of how to add this modification to the file?

Setting the devargs improves the rate with 512B frames, but degrades it with lower frame sizes.

[hhaim]

v2.91 solves this