IntroductionIntroduction

Ways To Enhance Performance- 

1.Increase in clock rate

oBy reducing clock cycle time

oPerformance increased by increasing number of instructions executed per second

o H/w limitations limit this feature

IntroductionIntroduction

Ways To Enhance Performance- 

2.Cache hierarchies

oBy using cache memories

oFrequently used data is put in caches

oReduces average accesses time

IntroductionIntroduction

Ways To Enhance Performance- 

3.Pipelining

oMultiple instructions are overlapped in execution

oLimited by the dependencies between instructions

oBasis for multi-threading.

Instruction Level Instruction Level ParallelismParallelism

o To increase the number of instructions executed in each clock cycle.

o It should be possible to simultaneously execute instructions.

Thread level parallelism

Chip Multi Processing

o Two or more processors

o Each has full set of execution and architectural

resources,.

o Are put together in a single die.

Thread level parallelism

Time Slice Multi Threading

o Only one processor

o Multiple threads executed by switching

Thread level parallelism

Switch on Event Multi Threading

o Switch threads on long latency events such as

cache misses

Hyper-Threading Hyper-Threading TechnologyTechnology

Hyper-Threading Technology first invented by

Intel Corp.

Brings the simultaneous multi-threading

approach to the Intel architecture.

A single physical processor appears like two or

more logical processors

Hyper-Threading Hyper-Threading TechnologyTechnology

Provides thread-level-parallelism (TLP) on each

processor

TLP results in increased utilization of processor

and execution resources.

Each logical processor maintain one copy of

the architecture state

Processor Execution Resources

Processor Execution Resources

Arch State Arch State Arch State

Processor with out Hyper-Threading Technology

Processor with Hyper-Threading Technology

Hyper-Threading Technology Architecture

Sharing of ResourcesSharing of Resources

       Major Sharing Schemes are-

o Partitiono Thresholdo Full Sharing

Partition

     Each logical processor uses half the resources

     Simple and low in complexity      Ensures fairness and progress      Good for major pipeline queues

Partitioned Queue ExamplePartitioned Queue Example

Yellow thread – It is faster threadGreen thread – It is slower thread

ThresholdThreshold

  Puts a threshold on number of resource entries a

logical processor can use.

Limits maximum resource usage

For small structures where resource utilization in burst and time of utilization is short, uniform and predictable

  E g - Processor Scheduler

Full Sharing Full Sharing   

  Most flexible mechanism for resource sharing, do not limit the maximum uses for resource usage for a logical processor

 Good for large structures in which working set sizes are variable and there is no fear of starvation

  E g : All Processor caches are shared

Single-Task & Multi-Task ModesSingle-Task & Multi-Task Modes

SINGLE-TASK AND MULTI-TASK MODESSINGLE-TASK AND MULTI-TASK MODES

Operating systemOperating system For best performance, the operating system

should implement two optimizations.

◦ The first is to use the HALT instruction if one logical processor is active and the other is not. HALT will allow the processor to transition MT mode to either the ST0- or ST1-mode.

◦ The second optimization is in scheduling software threads to logical processors. The operating system should schedule threads to logical processors on different physical processors before scheduling two threads to the same physical processor.

Business Benefits of Hyper-Threading Business Benefits of Hyper-Threading TechnologyTechnology

Higher transaction rates for e-Businesses

Improved reaction and response times for end-users and customers.

Increased number of users that a server system can support

Handle increased server workloads

Compatibility with existing server applications and operating systems

LimitationsLimitations

Hyper-Threading technology cannot beat dual processors in terms of performance.

Performance to cost ratio is much higher. Hyper-Threading does not get 2x faster, but

neither do dual CPU systems

ConclusionConclusion

• Intel’s Hyper-Threading Technology brings the concept of simultaneous multi-threading to the Intel Architecture.

• It will become increasingly important going forward as it adds a new technique for obtaining additional performance for lower transistor and power costs.

• The goal was to implement the technology at minimum cost while ensuring forward progress on logical processors, even if the other is stalled, and to deliver full performance even when there is only one active logical processor.

ReferencesReferences

“HYPER-THREADING TECHNOLOGY ARCHITECTURE AND

MICROARCHITECTURE” by Deborah T. Marr, Frank Binns, David L. Hill,

Glenn Hinton,David A. Koufaty, J. Alan Miller, Michael Upton, intel Technology

Journal, Volume 06 Issue 01, Published February 14, 2002. Pages: 4 –15.

“:HYPERTHREADING TECHNOLOGY IN THE NETBURST

MICROARCHITECTURE” by David Koufaty,Deborah T. Marr, IEEE

Micro, Vol. 23, Issue 2, March–April 2003. Pages: 56 – 65.

http://cache-www.intel.com/cd/00/00/22/09/220943_220943.pdf

http://www.cs.washington.edu/research/smt/papers/tlp2ilp.final.pdf

http://mos.stanford.edu/papers/mj_thesis.pdf