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[MX] line-rate frame size throughput is not 100% at 64/100 byte

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Article ID: KB33477 KB Last Updated: 29 Jun 2019Version: 2.0
Summary:

On summit MX204 and MX10003 platforms, the line rate frame size is 119 byte for 10/40GbE port and 95 byte for 100GbE port.

Symptoms:

When different frame size performance is tested on summit MX204 and MX10003 platforms with bi-directional single stream Ipv4 traffic between two 10GE interfaces, the throughput is 100% at 256/1514/9100 byte as expected. However, the throughput is not 100% at 64/100 byte.

Solution:

This is a known design limitation of EA chip on summit MX platforms. The design of the EA ASIC’s WO (WAN Output) block uses a design technique called TDM (Time Division Multiplexing) to reduce the amount of logic and SRAM needed for the implementation. 

The line rate frame size for 10GE port is 119 byte on summit MX platforms. They are not good at transferring short frames.

We do not recognize any significant performance delta between Hyper-mode and normal-mode in this scenario.

The following table summarizes the line rate frame size supported by summit MX platforms:

Port speed      Minimum L2 Line Rate frame size supported
---------------------------------------------------------
10GbE           119Byte
40GbE           119Byte
100GbE           95Byte

From Junos 19.1R1, we support "High-performance mode" to enable WAN Output block resource allocation. In this mode, better throughput is achieved at line-rate traffic for small sized packets.

The following indicates that High-performance mode is supported on PFE0 and PFE1 of fpc 5:

Configuration:

set chassis fpc <slot_no> pic <pic_slot> pic-mode<pic_mode>
set chassis fpc <slot_no> pic <pic_slot> number-of-ports<port_count>

Commands:

mx10003> show chassis fpc 5 detail
Slot 5 information:
State                               Online
Temperature                      35 degrees C / 95 degrees F
Total CPU DRAM                 2048 MB
Total RLDRAM                    331 MB
Total DDR DRAM                 1536 MB
FIPS Capable                        False
FIPS Mode                           False
Start time                          2018-08-16 00:17:00 PDT
Uptime                              7 hours, 25 minutes, 20 seconds
Max power consumption            227 Watts
High-Performance mode support       True
PFEs in High-Performance mode       PFE0, PFE1

Modification History:

2019-06-29: Updated solution.

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