Enable/Disable/Tune DDIO

what is DDIO?

• please read this repo and this paper

How to Modify setting?

Each platform has its own setting policy, following is our platform

	CPU	MotherBoard	Memory
Name	Intel Xeon Silver 4214	X11DPG-OT-CPU	DDR4 2400*8

Get DDIO setting

1. install msr-tools, e.g.(debian) sudo apt install msr-tools
2. enable linux kernel module msr, e.g. sudo modprobe msr
3. use sudo rdmsr -a 0xc8b to get current setting

You will get a num like 600 and regard it as bitmask to allocate LLC ways.

Tune DDIO setting

1. use sudo wrmsr -a 0xc8b 0x600 to set, 0x600 is the value you get from rdmsr command, range from 0x600 to 0x7ff(LLC n-ways associations)

Disable DDIO

Check ddio-modify.cpp to see details

cd /path/to/repo && mkdir build && cd build && cmake .. && make
sudo ./ddio_modify --enable=false --nic_bus=0x3a

Enalbe DDIO

#same as disable, but use following command
sudo ./ddio_modify --enable=true --nic_bus=0x3a

What is --nic_bus?

According to this document , we need set proper value to PERFCTRLSTS_0 field, which belong to a root bus device. So we need set --nic_bus to the bus number of the root bus device.

As we know, PCIE is a tree structure, and the root bus device belongs to the children of root. So we can use lspci -v -t to check which root bus device is the grandparent of target NIC.

On our platform, this target root bus device is 0x3a.