Hyper threading

1. MAHARANA PRATAP COLLEGE OF
TECHNOLOGY
Hyper-threading
B.E.(508)
Submitted To :- Sarika Tyagi Submitted By:- Anmol
Purohit
Depart. :- C.S. Roll No. :- 0903CS121019

2. TO BE TACKLED
• Introduction
• Hyper-Threading Concepts
• How Hyper Threading Works
• Implementing Hyper-threading
• Hyper-Threading Architecture
• Applications
• Advantages/Disadvantages
• Conclusion
• References

3. INTRODUCTION
• Hyper-Threading Technology brings the simultaneous multi-threading
approach to the Intel architecture that allows processors to work more
efficiently.
• This new technology enables the processor to execute two series, or
threads, of instructions at the same time, thereby
improving performance and system responsiveness while delivering
performance headroom for the future.
• Hyper-Threading Technology provides thread-level-parallelism (TLP) on
each processor resulting in increased utilization of processor and
execution resources.
• Hyper-Threading Technology provides two logical processors in a single
processor package.

4. HYPER-THREADING CONCEPT
• At each point of time only a part of processor resources is
used for execution of the program code.
• Unused resources can also be loaded, for example, with
parallel execution of another thread/application.
• Extremely useful in desktop and server applications where
many threads are used.
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5. HOW HYPER THREADING WORKS
• A single processor supporting Hyper-Threading Technology presents
itself to modern operating systems and applications as two virtual
processors. The processor can work on two sets of tasks
simultaneously, use resources that otherwise would sit idle, and get
more work done in the same amount of time.
• HT Technology takes advantage of the multithreading capability that's
built in to Windows XP and many advanced applications. Multithreaded
software divides its workloads into processes and threads that can be
independently scheduled and dispatched. In a multiprocessor system,
those threads execute on different processors.

7. IMPLEMENTING HYPER-THREADING
• Replicated :- Register renaming logic, instruction pointer,
ITLB, return stack predictor, Various other architectural registers
• Partitioned :- Re-order buffers, load/store buffer, various
queues :scheduling queue, uop queue
• Shared :- Caches: Trace Cache, L1,L2,L3, Micro-
Architectural registers , Execution Units

8. REPLICATED RESOURCES
 Necessary in order to maintain two fully independent contexts on
each logical processor.
 The most obvious of these is the instruction pointer (IP), which is the
pointer that helps the processor keep track of its place in the
instruction stream by pointing to the next instruction to be fetched.
 In order to run more than one process on the CPU, you need as
many IPs as there are instruction streams keep track of. Or,
equivalently, you could say that you need one IP for each logical
processor.
 Similarly, the Xeon has two register allocation tables (RATs), each of
which handles the mapping of one logical processor's eight
architectural integer registers and eight architectural floating-point
registers onto a shared pool of 128 GPRs (general purpose registers)
and 128 FPRs (floating-point registers). So the RAT is a replicated
resource that manages a shared resource (the micro architectural
register file).

9. PARTITIONED RESOURCES
 Statically partitioned queue
 Each queue is split in half
 It’s resources solely dedicated
to use of one logical processor

10. PARTITIONED RESOURCES
 Dynamically partitioned queue
 In a scheduling queue with 12
entries, instead of assigning
entries 0 through 5 to logical
processor 0 and entries 6
through 11 to logical processor
1, the queue allows any logical
processor to use any entry but
it places a limit on the number
of entries that any one logical
processor can use. So in the
case of a 12-entry scheduling
queue, each logical processor
can use no more than six of the
entries.

11. SHARED RESOURCES
• Shared resources are at the heart of hyper-threading; they're what
makes the technique worthwhile.
• The more resources that can be shared between logical processors,
the more efficient hyper-threading can be at squeezing the maximum
amount of computing power out of the minimum amount of die space.
• A class of shared resources consists of the execution units: the
integer units, floating-point units, and load-store unit.
• Hyper-threading's greatest strength--shared resources--also turns out
to be its greatest weakness, as well.
• Problems arise when one thread monopolizes a crucial resource. The
problem here is the exact same problem that we discussed with
cooperative multi-tasking: one resource hog can ruin things for
everyone else. Like a cooperative multitasking OS, the Xeon for the
most part depends on each thread to play nicely and to refrain from
monopolizing any of its shared resources.

12. HYPER-THREADING
ARCHITECTURE
• First used in Intel Xeon MP processor
• Makes a single physical processor appear as multiple
logical processors.
• Each logical processor has a copy of architecture state.
• Logical processors share a single set of physical execution
resources
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13. 13

14. APPLICATION
• The Intel Xeon processor with Hyper-Threading Technology is well-suited
for servers and high-end scientific computing workstations, as
well as demanding applications such as graphics, multimedia, and
gaming.
• Business Benefits

15. BUSINESS BENEFITS OF HYPER-THREADING
TECHNOLOGY
• 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

16. ADVANTAGES
• No performance loss if only one thread is active. Increased
performance with multiple threads
• Improved overall system performance
• Increased number of users a platform can support
• Improved throughput, because tasks run on separate threads
• Improved reaction and response time
• Increased number of transactions that can be executed
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17. DISADVANTAGES
• To take advantage of hyper-threading performance, serial
execution can not be used.
• Threads are non-deterministic and involve extra design
• Threads have increased overhead
• Shared resource conflicts
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18. CONCLUSION
• 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.

19. REFERENCES
• Intel Technology Journal. Volume 6 Issue 1. February 14,
2002
• Intel Hyper-Threading Technology Review
• www.digit-life.
com/articles/pentium4xeonhyperthreading/
• HyperThreading Threads Its Way into Application
• http://www.tomshardware.com/cpu/20021227/
• Introduction to Multithreading, Superthreading and
Hyperthreading
• http://www.arstechnica.com/paedia/h/hyperthreading/h
yperthreading-1.html
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20. Thank you