Dr. Dobb's Journal - September 2008 - (Page 50)

d09levent_p3db 7/14/08 10:00 AM Page 50 State of the Art MANAGING APPLICATION THREAD USE response request governor request response 100 CPU Idle Time 80 70 50 40 int_thread_count Update Interval Loadi set_thread_count Governor: • Periodically monitor CPU idle and system times • Update number of available processors based on the idle time threshold • If there is request from a load, return number of available processors Figure 1: Block diagrams showing the framework (loads are the applications). Loads: • Get initial thread count from the governor (int_thread_count) • Periodically check with governor and get number of processors available • Set number of threads (set_thread_count) continued from page 48 Update available processor periodically signal Governor daemon waits for update requests accordingly. The communication takes place via sockets over TCP/IP. All applications set the number of threads to use for parallel regions (in the OpenMP sense), based on the feedback received from the governor, rather than setting the number of threads as the number of processors physically available or as they wish. Also, applications only increase their thread count, but can’t set it more than the physical number of cores. This makes the initial thread count with which the application starts worth mentioning. Refresh Interval Read number of processors available Update Stats Applications The Load Governor The load governor (Figure 2) uses a basic metric—processor idle time—to compute system utilization. Based on the idle time, the governor identifies available cores and returns the number of available cores to the requesting applications. For example, if the idle threshold is set to 5, the governor marks all cores that are idle 5 percent or more of their time as available (95 percent or less utilized) at the time of the snapshot. The processor statistics (system time, idle time, and so on) are collected from /proc/stats periodically (with Linux); this period can be adjusted as a parameter to the governor. Evaluate number of available cores Figure 2: Block diagram showing the internals of the load governor. 50 Dr. Dobb’s Journal l www.ddj.com l September 2008 http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - September 2008

Dr. Dobb's Journal - September 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Developer’s Notebook A Conversation With Erik Demaine Application Lifecycle Management Meets Model-Driven Development Building a Robust Development Environment Real Users Really Matter Matching Wildcards: An Algorithm The Android Mobile Phone Platform Managing Application Thread Use Signalling Integer Overflows in Java .NET Development & the IBM WebSphere Portal Server The Agile Edge Effective Concurrency Swaine’s Flames

Dr. Dobb's Journal - September 2008

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