1. Computers
  2. Display Drivers
  3. Graphics Cards
  4. Memory
  5. Motherboards
  6. Processors
  7. Software
  8. Storage
  9. Operating Systems


Facebook RSS Twitter Twitter Google Plus


Phoronix Test Suite

OpenBenchmarking.org

Intel Developer Proposes A New Linux CPU Load Metric

Intel

Published on 25 April 2014 01:22 AM EDT
Written by Michael Larabel in Intel
1 Comment

A Linux developer at Intel has proposed a new CPU load metric for power-efficient scheduling by the Linux kernel.

The new metric is called CPU ConCurrency. Using this metric for power-efficient scheduling, Intel developers implemented a workload consolidation patch for two mobile Intel platforms. The work contains the load and load balancing to two cores when the aggregated CPU ConCurrency is low while when it's high all four CPU cores are used for scheduling. This change led to increased power-savings while no significant performance regessions were spotted.

Intel Developer Proposes A New Linux CPU Load Metric


Intel's Yuyang Du explained CPU ConCurrency on the kernel mailing list. Here's the full explanation:
The current scheduler’s load balancing is completely work-conserving. In some workload, generally low CPU utilization but immersed with CPU bursts of transient tasks, migrating task to engage all available CPUs for work-conserving can lead to significant overhead: cache locality loss, idle/active HW state transitional latency and power, shallower idle state, etc, which are both power and performance inefficient especially for today’s low power processors in mobile.

This RFC introduces a sense of idleness-conserving into work-conserving (by all means, we really don’t want to be overwhelming in only one way). But to what extent the idleness-conserving should be, bearing in mind that we don’t want to sacrifice performance? We first need a load/idleness indicator to that end.

Thanks to CFS’s "model an ideal, precise multi-tasking CPU", tasks can be seen as concurrently running (the tasks in the runqueue). So it is natural to use task concurrency as load indicator. Having said that, we do two things:

1) Divide continuous time into periods of time, and average task concurrency in period, for tolerating the transient bursts: a = sum(concurrency * time) / period
2) Exponentially decay past periods, and synthesize them all, for hysteresis to load drops or resilience to load rises (let f be decaying factor, and a_x the xth period average since period 0): s = a_n + f^1 * a_n-1 + f^2 * a_n-2 +, …..,+ f^(n-1) * a_1 + f^n * a_0

We name this load indicator as CPU ConCurrency (CC): task concurrency determines how many CPUs are needed to be running concurrently.

To track CC, we intercept the scheduler in 1) enqueue, 2) dequeue, 3) scheduler tick, and 4) enter/exit idle.

By CC, we implemented a Workload Consolidation patch on two Intel mobile platforms (a quad-core composed of two dual-core modules): contain load and load balancing in the first dual-core when aggregated CC low, and if not in the full quad-core. Results show that we got power savings and no substantial performance regression (even gains for some).

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
Latest Linux Hardware Reviews
  1. A Walkthrough Of The New 32 System Open-Source Linux Benchmarking Test Farm
  2. Habey MITX-6771: Mini-ITX Board With Quad-Core J1900 Bay Trail
  3. OCZ Vector 150 SSD On Linux
  4. Noctua i4 CPU Cooler: Great For Cooling High-End LGA-2011v3 CPUs
Latest Linux Articles
  1. 17-Way Linux Graphics Card Comparison With Civilization Beyond Earth
  2. AMD Kaveri: Open-Source Radeon Gallium3D vs. Catalyst 14.12 Omega Driver
  3. 12-Way AMD Catalyst 14.12 vs. NVIDIA 346 Series Linux GPU Comparison
  4. AMD Catalyst 14.12 Omega Driver Brings Mixed Results For Linux Users
Latest Linux News
  1. Server-Side XCB Is Being Discussed For The X.Org Server
  2. Adreno A4xx Rendering With Freedreno Takes Shape
  3. Linux 3.19-rc1 Kernel Released Ahead Of Schedule
  4. Civilization: Beyond Earth Linux GPU/Driver Benchmarks
  5. X.Org Server 1.16.3 Released To Fix Security Issues
  6. Linux 3.19 Merge Window Closes Ahead Of Schedule
  7. MIPS R6 Architecture Now Supported By GCC
  8. LowRISC To Feature Tagged Memory & Minion Cores
  9. Intel Skylake Audio Support For Linux 3.19
  10. After 10+ Years, NetworkManager Reaches v1.0
Latest Forum Discussions
  1. Speeding up systemd networking service
  2. Need some hand holding with upgrading xserver
  3. FPS capped on Linux (AMD fglrx drivers)
  4. Are there an app using HSA ?
  5. The New SuperTuxKart Looks Better, But Can Cause GPU/Driver Problems
  6. XLennart: A Game For Systemd Haters With Nothing Better To Do
  7. Updated and Optimized Ubuntu Free Graphics Drivers
  8. Debian init discussion in Phoenix Wright format