Linux Kernel Network Subsystem Patching

[Aruna Hewapathirane]

*Bit of a read but truly helped me to understand Hyperthreading vs
Multi-threading vs Super Threading, may help others so sharing : *

Hyper-threading is using one processor but logically dividing it into two
so that it gives the user the benefit of two processors with only using the
resources equivalent to almost one.

This is achieved by sharing, partitioning and duplicating the various
resources almost into two processors. Used by the latest Pentium
processors, which are HT enabled, in layman's terms, it allows you to use
more than two applications
at the same time without slowing down processing speed.

Multi-threading is when various processes are time sliced such that it
gives the user the impression that all the programs are being run at the
same time. This is what happens on your computer regularly.

Super-threading allows threads from different processes to be executed at
the same time unlike Multi-threading where every process has a time slot
during which, thread from only one process will be executed. But every
time, if for example, there are four instructions issued to the processor.
They will all be from the same process. Hyper-threading takes it a step
further. It allows threads from different processes to be issued at the
same time, in turn, utilizing the waste cycles of the processor. You can go
to any Intel site for further info on this.

Another answer: Super-threading is a multithreading approach that weaves
together the execution of different threads on a single processor without
truly executing them at the same time. This qualifies it as time-sliced or
temporal multithreading rather than simultaneous multithreading.

It is motivated by the observation that the processor is occasionally left
idle while executing an instruction from one thread. Super-threading seeks
to make use of unused processor cycles by applying them to the execution of
an instruction from another thread.

Multithreading computers have hardware support to efficiently execute
multiple threads. These are distinguished from multiprocessing systems
(such as multi-core systems)  in that the threads have to share the
resources of single core: the computing units, the CPU caches and the
translation lookaside buffer (TLB).

Where multiprocessing systems include multiple complete processing units,
multithreading aims to increase utilization of a single core by leveraging
thread-level as well as instruction-level parallelism.

As the two techniques are complementary, they are sometimes combined in
systems with multiple multithreading CPUs and in CPUs with multiple
multithreading cores. Hyper-threading is Intel's trademarked term for its
simultaneous multithreading implementation in their Pentium 4, Atom, Core
i7, and certain Xeon CPUs. Hyper-threading (officially termed
Hyper-Threading
Technology or HTT) is an Intel-proprietary technology used to improve
parallelization of computations (doing multiple tasks at once) performed on
PC microprocessors.

A processor with hyper-threading enabled is treated by the operating system
as two processors instead of one. This means that only one processor is
physically present but the operating system sees two virtual  processors,
and shares the
workload between them.

*Hyper-threading requires both operating system and CPU support for
efficient usage; conventional multiprocessor support is not enough, and may
actually decrease performance if  the Operating System is not sufficiently
aware of the distinction between a physical core and a HTT-enabled core.*

For example, Intel does not recommend that physical core and a HTT-enabled
core. For example, Intel does not recommend that hyper-threading be enabled
under Windows 2000, even though the operating system supports multiple CPUs
(but is not HTT-aware).

Original article/slides here :
http://wiki.answers.com/Q/What_is_the_difference_between_hyper-threading_multi-threading_and_super-threading_in_computer_processors?#slide=1

Aruna


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