IBM BladeCenter PS700 User Manual

Chapter 2. Architecture and technical overview 41
2.2.3 Simultaneous multithreading
An enhancement in the POWER7 processor is the addition of the SMT4 mode to enable four
instruction threads to execute simultaneously in each POWER7 processor core. Thus, the
instruction thread execution modes of the POWER7 processor are as follows:
򐂰 SMT1: single instruction execution thread per core
򐂰 SMT2: two instruction execution threads per core
򐂰 SMT4: four instruction execution threads per core
SMT4 mode enables the POWER7 processor to maximize the throughput of the processor
core by offering an increase in processor-core efficiency. SMT4 mode is the latest step in an
evolution of multithreading technologies introduced by IBM. Figure 2-3 shows the evolution of
simultaneous multithreading.
Figure 2-3 Evolution of simultaneous multithreading
The various SMT modes offered by the POWER7 processor allow flexibility, enabling users to
select the threading technology that meets an aggregation of objectives (such as
performance, throughput, energy use, and workload enablement).
Intelligent threads
The POWER7 processor features intelligent threads that can vary based on the workload
demand. The system either automatically selects (or the system administrator can manually
select) whether a workload benefits from dedicating as much capability as possible to a single
thread of work, or if the workload benefits more from having capability spread across two or
four threads of work. With more threads, the POWER7 processor can deliver more total
capacity as more tasks are accomplished in parallel. With fewer threads, workloads that need
fast individual tasks can get the performance they need for maximum benefit.
Multi-threading Evolution
Thre ad 1 Ex ecu ti ng
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1995 Single thread out of order
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1997 Hardware muti-thread
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2003 2 Way SMT
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2009 4 Way SMT
Thread 3 Executing
Thre ad 2 Ex ecu ti ng

IBM BladeCenter PS700 Specifications

General

Brand	IBM
Model	BladeCenter PS700
Category	Server
Language	English