L27 - Additional Reference ECS 154B Computer Architecture...

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1 ECS 154B Computer Architecture II Winter 2008 Multiprocessor Synchronization Adapted from slides by Mary Jane Irwin, Penn State 2 Additional Reference • Some information and more details provided in Parallel Computer Architecture by David Culler, Jaswinder Pal Singh, and Anoop Gupta • Sections 5.3, 5.5, 6.3 • Available in library reserves 3 Process Synchronization • Processes must coordinate when working on a common task Mutual Exclusion (semaphores) • Provides access to only one process • Binary value • For example, access to a shared resource Barrier or Event Synchronization • Ensures all processes reach the same point before proceeding • Possibly multiple values • For example, compute partial sums before continuing • Provided through hardware support and variables 4 Main Actions for Synchronization • Acquire: how to obtain a synchronization element – Bus provides serialization of access attempts – Hardware must provide some atomic operations (actions that are guaranteed to complete before subsequent operations occur) • Wait: how a process waits for the signal to continue – Polling or busy waiting: process continually checks for access – Blocking: process stalls until signaled to continue • Release: how processes know to continue – Notify one process explicitly – Notify many processes implicitly
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2 5 Mutual Exclusion • Hardware locks possible – Only a limited number possible in hardware • Require bus signal lines • Can’t be changed after system is built – Not flexible to process workload requirements • Waste for workloads that don’t need as many locks • Insufficient for workloads than need many locks; have to use software locks anyway
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L27 - Additional Reference ECS 154B Computer Architecture...

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