178. Power Lib Empty Poll Test

178.1. Inband Policy Control

For packet processing workloads such as DPDK polling is continuous. This means CPU cores always show 100% busy independent of how much work those cores are doing. It is critical to accurately determine how busy a core is hugely important for the following reasons:

  • No indication of overload conditions
  • User do not know how much real load is on a system meaning resulted in wasted energy as no power management is utilized

Tried and failed schemes include calculating the cycles required from the load on the core, in other words the busyness. For example, how many cycles it costs to handle each packet and determining the frequency cost per core. Due to the varying nature of traffic, types of frames and cost in cycles to process, this mechanism becomes complex quickly where a simple scheme is required to solve the problems.

For all polling mechanism, the proposed solution focus on how many times empty poll executed instead of calculating how many cycles it cost to handle each packet. The less empty poll number means current core is busy with processing workload, therefore, the higher frequency is needed. The high empty poll number indicate current core has lots spare time, therefore, we can lower the frequency.

2.1 Power state definition:

LOW: the frequency is used for purge mode.

MED: the frequency is used to process modest traffic workload.

HIGH: the frequency is used to process busy traffic workload.

2.2 There are two phases to establish the power management system:

a.Initialization/Training phase. There is no traffic pass-through, the system will test average empty poll numbers with LOW/MED/HIGH power state. Those average empty poll numbers will be the baseline for the normal phase. The system will collect all core’s counter every 100ms. The Training phase will take 5 seconds.

b.Normal phase. When the real traffic pass-though, the system will compare run-time empty poll moving average value with base line then make decision to move to HIGH power state of MED power state. The system will collect all core’s counter every 10ms.

training_flag
: optional, enable/disable training mode. Default value is 0.
If the training_flag is set as 1(true), then the application will start in training mode and print out the trained threshold values. If the training_flag is set as 0(false), the application will start in normal mode, and will use either the default thresholds or those supplied on the command line. The trained threshold values are specific to the user’s system, may give a better power profile when compared to the default threshold values.

med_threshold : optional, sets the empty poll threshold of a modestly busy system state. If this is not supplied, the application will apply the default value of 350000.

high_threshold : optional, sets the empty poll threshold of a busy system state. If this is not supplied, the application will apply the default value of 580000.

178.2. Preparation Work for Settings

BIOS setting:

1. Turn on Speedstep option in BIOS
2. Turn on Turbo in BIOS
3. Turn off Hyper Threading

Linux setting:

1. Use intel_pstate driver for CPU frequency control
2. modprobe msr

sys_min=/sys/devices/system/cpu/cpu{}/cpufreq/cpuinfo_min_freq sys_max=/sys/devices/system/cpu/cpu{}/cpufreq/cpuinfo_max_freq no_turbo_max=$(rdmsr -p 1 0x0CE -f 15:8 -d)00000

cur_min=/sys/devices/system/cpu/cpu{}/cpufreq/scaling_min_freq cur_max=/sys/devices/system/cpu/cpu{}/cpufreq/scaling_max_freq

178.3. Test Case1 : Basic Training mode test based on one NIC with l3fwd-power

Step 1. Bind One NIC to DPDK driver, launch l3fwd-power with empty-poll enabled

./l3fwd-power -l 1-2 -n 4 – -p 0x1 -P –config=”(0,0,2)” –empty-poll=”1,0,0” -l 10 -m 6 -h 1

Step 2. Check the log also when changing the inject packet rate as following:

Injected Rate(1024B, dst_ip=1.1.1.1): 10G -> 0.1G -> 10G -> 0.1G -> 10G -> 0.1G The frequency will be set to MED when we inject 0.1G and return to HGH when inject 10G Rate, check the frequency of the forwarding core(core 2) When traffic is 10G: cur_min=cur_max=no_turbo_max When traffic is 0.1G: cur_min=cur_max=[no_turbo_max-500000]

178.4. Test Case2: No-Training mode test based on one NIC with l3fwd-power

Step 1. Bind One NIC to DPDK driver, launch l3fwd-power with empty-poll enabled

./l3fwd-power -l 1-2 -n 4 – -p 0x1 -P –config=”(0,0,2)” –empty-poll=”0,350000,500000” -l 10 -m 6 -h 1

Step 2. Check no training steps are executed in sample’s launch log.