01-03-2010, 11:27 PM
A SEMINAR REPORT ON
HYPER THREADING TECHNOLOGY
Submitted By:
Megha
Msc Comp Sc.
Abstract:
Intel Pentium 4 processor that incorporates Hyper-Threading Technology
Hyper-threading works by duplicating certain sections of the processorâ€those that store the architectural stateâ€but not duplicating the main execution resources. This allows a hyper-threading processor to appear as two "logical" Hyper threading technology
Hyper-threading (officially Hyper-Threading Technology, and abbreviated HT Technology, HTT or HT) is Intel's term for its simultaneous multithreading implementation in their Xeon, Pentium 4, Atom, Core i3, Core i5 and Core i7 CPUs.
Hyper-threading is an Intel-proprietary technology used to improve parallelization of computations (doing multiple tasks at once) performed on PC microprocessors. For each processor core that is physically present, the operating system addresses two virtual processors, and shares the workload between them when possible.
Hyper-threading requires only that the operating system support multiple processors, and Intel recommends disabling HTT when using operating systems that have not been optimized for the technology.
Another definition of Hyper Threading Technology
A technology developed by Intel that enables multithreaded software applications to execute threads in parallel on a single multi-core processor instead of processing threads in a linear fashion. Older systems took advantage of dual-processing threading in software by splitting instructions into multiple streams so that more than one processor could act upon them at once.
Performance
The advantages of hyper-threading are listed as: improved support for multi-threaded code, allowing multiple threads to run simultaneously, improved reaction and response time.
According to Intel the first implementation only used 5% more die area than the comparable non-hyperthreaded processor, but the performance was 15“30% better.
Intel claims up to a 30% performance improvement compared with an otherwise identical, non-simultaneous multithreading Pentium 4. Intel also claims significant performance improvements with a hyper-threading-enabled Pentium 4 processor in some artificial intelligence algorithms. The performance improvement seen is very application-dependent, however, and some programs actually slow down slightly when Hyper Threading Technology is turned on. This is due to the replay system of the Pentium 4 tying up valuable execution resources, thereby starving the other thread. (The Pentium 4 Prescott core gained a replay queue, which reduces execution time needed for the replay system, but this is not enough to completely overcome the performance hit.) However, any performance degradation is unique to the Pentium 4 (due to various architectural nuances), and is not characteristic of simultaneous multithreading in general.
Details
Processors to the host operating system, allowing the operating system to schedule two threads or processes simultaneously. When execution resources would not be used by the current task in a processor without hyper-threading, and especially when the processor is stalled, a hyper-threading equipped processor can use those execution resources to execute another scheduled task. (The processor may stall due to a cache miss, branch misprediction, or data dependency.)
This technology is transparent to operating systems and programs. All that is required to take advantage of hyper-threading is symmetric multiprocessing (SMP) support in the operating system, as the logical processors appear as standard separate processors.
It is possible to optimize operating system behavior on multi-processor hyper-threading capable systems. For example, consider an SMP system with two physical processors that are both hyper-threaded (for a total of four logical processors). If the operating system's process scheduler is unaware of hyper-threading it will treat all four processors as being the same. If only two processes are eligible to run it might choose to schedule those processes on the two logical processors that happen to belong to one of the physical processors; that processor would become extremely busy while the other would be idle, leading to poorer performance than is possible with better scheduling. This problem can be avoided by improving the scheduler to treat logical processors differently from physical processors; in a sense, this is a limited form of the scheduler changes that are required for NUMA systems.
Security
In May 2005 Colin Percival demonstrated that a malicious thread operating with limited privileges can monitor the execution of another thread through their influence on a shared data cache, allowing for the theft of cryptographic keys.[3] Note that while the attack described in the paper was demonstrated on an Intel Pentium 4 processor with HTT, the same techniques could theoretically apply to any system where caches are shared between two or more non-mutually-trusted execution threads; see also side channel attack.
Past
Hyper-Threading was first introduced in the Foster MP-based Xeon in 2002. It appeared on the 3.06 GHz Northwood-based Pentium 4 in the same year, and then appeared in every Pentium 4 HT, Pentium 4 Extreme Edition and Pentium Extreme Edition processor. Previous generations of Intel's processors based on the Core microarchitecture do not have Hyper-Threading, because the Core micro architecture is a descendant of the P6 micro architecture used in iterations of Pentium since the Pentium Pro through the Pentium III and the Celeron (Covington, Mendocino, Copper mine and Tualatin-based) and the Pentium II Xeon and Pentium III Xeon models. However, Intel is using the feature in the newer Atom and Core i7 processors.
Inefficiencies
In 2006 hyper-threading was criticized for being energy-inefficient. For example, specialist low-power CPU design company ARM has stated SMT can use up to 46% more power than dual core designs. Dual core processors are different than Dual CPU. Furthermore, they claim SMT increases cache thrashing by 42%, whereas dual core results in a 37% decrease.[4] These considerations are claimed to be the reason Intel dropped SMT from the Core 2 micro architecture.[by whom?]
Present & Future
Intel released the Nehalem (Core i7) in November 2008 in which hyper-threading makes a return. Nehalem contains 4 cores and effectively scales 8 threads.[5]
The Intel Atom is an in-order processor with hyper-threading, for low power mobile PCs and low-price desktop PCs.[6]
The Itanium 9300 launched with eight threads per processor through enhanced hyper-threading technology. Paulson, the next-generation Itanium, is schedule to have additional hyper-threading enhancements.[7]
The Intel Xeon 5500 server chips also utilize two-way hyper-threading[8][9]
Difference
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 EG, 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.
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.[1] 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
Disadvantages
Hyper-Threading is not SMP. (Symmetric Multi-Processing)implies several processors, and we have only one processor. However, it is supplemented with a certain feature which lets it pretend it consists of two processors.
Well, the Hyper-Threading technology allows increasing efficiency of the processor in certain cases. In particular, when applications of different nature are used simultaneously. This is an advantage, but the effect takes place only in certain situations. The classical market principle says: pay more to get more.
It really boosts up performance sometimes. The effect can be much greater than even when we compare two platforms with the same processor but different chipsets. But the effect depends on a style of working with a computer. Note that the classical SMP style is when a user counts on the response of the classical multiprocessor system.
The style of the Hyper-Threading is a combination of entertaining or service processes with "working" processes. You won't get a tangible gain in most classical multiprocessor tasks if you run one application at a time. But you will surely make shorter the time of execution of most background tasks used as a makeweight. Intel has actually reminded us that operating systems we are using are multitask, and it offered a way to speed up fulfillment of a complex of simultaneously executed applications (not a single one). This is a very interesting approach, and we are glad this idea is realized.
See also
¢ Multi-core
¢ Barrel processor
References
1. ^ Operating Systems that include optimizations for Hyper-Threading Technology
2. ^ Intel Processor Spec Finder: SL6WK
3. ^ Cache Missing for Fun and Profit
4. ^ theinquirer.net
5. ^ Intel explains the new Core i7 CPU
6. ^ http://inteltechnology/atom/microarchitecture.htm
7. ^ http://microelectronics.cbronlinenews/in...sor_100208
8. ^ http://intelp/en_US/products/server/processor
9. ^ http://intelbusiness/resources/demos/xeon5500/performance/demo.htm
External links
¢ Intel's high level overview of Hyper-threading
¢ Hyper-threading on MSDN Magazine
¢ HyperThreading Overview from OSDEV Community
¢ An introductory article from Ars Technica
¢ Hyper-Threading Technology Architecture and Microarchitecture, technical description of Hyper-Threading (1.2 MB PDF-file)
¢ [1] Enter Patent Number 4,847,755
¢ Merom, Conroe, Woodcrest lose HyperThreading
Security
¢ KernelTrap discussion: Hyper-Threading Vulnerability
Performance
¢ ZDnet: Hyperthreading hurts server performance, say developers
¢ ARM is no fan of HyperThreading
disadvantages
Hyper-Threading is not SMP. (Symmetric Multi-Processing)implies several processors, and we have only one processor. However, it is supplemented with a certain feature which lets it pretend it consists of two processors.
Well, the Hyper-Threading technology allows increasing efficiency of the processor in certain cases. In particular, when applications of different nature are used simultaneously. This is an advantage, but the effect takes place only in certain situations. The classical market principle says: pay more to get more.
It really boosts up performance sometimes. The effect can be much greater than even when we compare two platforms with the same processor but different chipsets. But the effect depends on a style of working with a computer. Note that the classical SMP style is when a user counts on the response of the classical multiprocessor system.
The style of the Hyper-Threading is a combination of entertaining or service processes with "working" processes. You won't get a tangible gain in most classical multiprocessor tasks if you run one application at a time. But you will surely make shorter the time of execution of most background tasks used as a makeweight. Intel has actually reminded us that operating systems we are using are multitask, and it offered a way to speed up fulfillment of a complex of simultaneously executed applications (not a single one). This is a very interesting approach, and we are glad this idea is realized.
for more please read
http://ixbtlabsarticles2/pentium43ghzht/
HYPER THREADING TECHNOLOGY
Submitted By:
Megha
Msc Comp Sc.
Abstract:
Intel Pentium 4 processor that incorporates Hyper-Threading Technology
Hyper-threading works by duplicating certain sections of the processorâ€those that store the architectural stateâ€but not duplicating the main execution resources. This allows a hyper-threading processor to appear as two "logical" Hyper threading technology
Hyper-threading (officially Hyper-Threading Technology, and abbreviated HT Technology, HTT or HT) is Intel's term for its simultaneous multithreading implementation in their Xeon, Pentium 4, Atom, Core i3, Core i5 and Core i7 CPUs.
Hyper-threading is an Intel-proprietary technology used to improve parallelization of computations (doing multiple tasks at once) performed on PC microprocessors. For each processor core that is physically present, the operating system addresses two virtual processors, and shares the workload between them when possible.
Hyper-threading requires only that the operating system support multiple processors, and Intel recommends disabling HTT when using operating systems that have not been optimized for the technology.
Another definition of Hyper Threading Technology
A technology developed by Intel that enables multithreaded software applications to execute threads in parallel on a single multi-core processor instead of processing threads in a linear fashion. Older systems took advantage of dual-processing threading in software by splitting instructions into multiple streams so that more than one processor could act upon them at once.
Performance
The advantages of hyper-threading are listed as: improved support for multi-threaded code, allowing multiple threads to run simultaneously, improved reaction and response time.
According to Intel the first implementation only used 5% more die area than the comparable non-hyperthreaded processor, but the performance was 15“30% better.
Intel claims up to a 30% performance improvement compared with an otherwise identical, non-simultaneous multithreading Pentium 4. Intel also claims significant performance improvements with a hyper-threading-enabled Pentium 4 processor in some artificial intelligence algorithms. The performance improvement seen is very application-dependent, however, and some programs actually slow down slightly when Hyper Threading Technology is turned on. This is due to the replay system of the Pentium 4 tying up valuable execution resources, thereby starving the other thread. (The Pentium 4 Prescott core gained a replay queue, which reduces execution time needed for the replay system, but this is not enough to completely overcome the performance hit.) However, any performance degradation is unique to the Pentium 4 (due to various architectural nuances), and is not characteristic of simultaneous multithreading in general.
Details
Processors to the host operating system, allowing the operating system to schedule two threads or processes simultaneously. When execution resources would not be used by the current task in a processor without hyper-threading, and especially when the processor is stalled, a hyper-threading equipped processor can use those execution resources to execute another scheduled task. (The processor may stall due to a cache miss, branch misprediction, or data dependency.)
This technology is transparent to operating systems and programs. All that is required to take advantage of hyper-threading is symmetric multiprocessing (SMP) support in the operating system, as the logical processors appear as standard separate processors.
It is possible to optimize operating system behavior on multi-processor hyper-threading capable systems. For example, consider an SMP system with two physical processors that are both hyper-threaded (for a total of four logical processors). If the operating system's process scheduler is unaware of hyper-threading it will treat all four processors as being the same. If only two processes are eligible to run it might choose to schedule those processes on the two logical processors that happen to belong to one of the physical processors; that processor would become extremely busy while the other would be idle, leading to poorer performance than is possible with better scheduling. This problem can be avoided by improving the scheduler to treat logical processors differently from physical processors; in a sense, this is a limited form of the scheduler changes that are required for NUMA systems.
Security
In May 2005 Colin Percival demonstrated that a malicious thread operating with limited privileges can monitor the execution of another thread through their influence on a shared data cache, allowing for the theft of cryptographic keys.[3] Note that while the attack described in the paper was demonstrated on an Intel Pentium 4 processor with HTT, the same techniques could theoretically apply to any system where caches are shared between two or more non-mutually-trusted execution threads; see also side channel attack.
Past
Hyper-Threading was first introduced in the Foster MP-based Xeon in 2002. It appeared on the 3.06 GHz Northwood-based Pentium 4 in the same year, and then appeared in every Pentium 4 HT, Pentium 4 Extreme Edition and Pentium Extreme Edition processor. Previous generations of Intel's processors based on the Core microarchitecture do not have Hyper-Threading, because the Core micro architecture is a descendant of the P6 micro architecture used in iterations of Pentium since the Pentium Pro through the Pentium III and the Celeron (Covington, Mendocino, Copper mine and Tualatin-based) and the Pentium II Xeon and Pentium III Xeon models. However, Intel is using the feature in the newer Atom and Core i7 processors.
Inefficiencies
In 2006 hyper-threading was criticized for being energy-inefficient. For example, specialist low-power CPU design company ARM has stated SMT can use up to 46% more power than dual core designs. Dual core processors are different than Dual CPU. Furthermore, they claim SMT increases cache thrashing by 42%, whereas dual core results in a 37% decrease.[4] These considerations are claimed to be the reason Intel dropped SMT from the Core 2 micro architecture.[by whom?]
Present & Future
Intel released the Nehalem (Core i7) in November 2008 in which hyper-threading makes a return. Nehalem contains 4 cores and effectively scales 8 threads.[5]
The Intel Atom is an in-order processor with hyper-threading, for low power mobile PCs and low-price desktop PCs.[6]
The Itanium 9300 launched with eight threads per processor through enhanced hyper-threading technology. Paulson, the next-generation Itanium, is schedule to have additional hyper-threading enhancements.[7]
The Intel Xeon 5500 server chips also utilize two-way hyper-threading[8][9]
Difference
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 EG, 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.
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.[1] 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
Disadvantages
Hyper-Threading is not SMP. (Symmetric Multi-Processing)implies several processors, and we have only one processor. However, it is supplemented with a certain feature which lets it pretend it consists of two processors.
Well, the Hyper-Threading technology allows increasing efficiency of the processor in certain cases. In particular, when applications of different nature are used simultaneously. This is an advantage, but the effect takes place only in certain situations. The classical market principle says: pay more to get more.
It really boosts up performance sometimes. The effect can be much greater than even when we compare two platforms with the same processor but different chipsets. But the effect depends on a style of working with a computer. Note that the classical SMP style is when a user counts on the response of the classical multiprocessor system.
The style of the Hyper-Threading is a combination of entertaining or service processes with "working" processes. You won't get a tangible gain in most classical multiprocessor tasks if you run one application at a time. But you will surely make shorter the time of execution of most background tasks used as a makeweight. Intel has actually reminded us that operating systems we are using are multitask, and it offered a way to speed up fulfillment of a complex of simultaneously executed applications (not a single one). This is a very interesting approach, and we are glad this idea is realized.
See also
¢ Multi-core
¢ Barrel processor
References
1. ^ Operating Systems that include optimizations for Hyper-Threading Technology
2. ^ Intel Processor Spec Finder: SL6WK
3. ^ Cache Missing for Fun and Profit
4. ^ theinquirer.net
5. ^ Intel explains the new Core i7 CPU
6. ^ http://inteltechnology/atom/microarchitecture.htm
7. ^ http://microelectronics.cbronlinenews/in...sor_100208
8. ^ http://intelp/en_US/products/server/processor
9. ^ http://intelbusiness/resources/demos/xeon5500/performance/demo.htm
External links
¢ Intel's high level overview of Hyper-threading
¢ Hyper-threading on MSDN Magazine
¢ HyperThreading Overview from OSDEV Community
¢ An introductory article from Ars Technica
¢ Hyper-Threading Technology Architecture and Microarchitecture, technical description of Hyper-Threading (1.2 MB PDF-file)
¢ [1] Enter Patent Number 4,847,755
¢ Merom, Conroe, Woodcrest lose HyperThreading
Security
¢ KernelTrap discussion: Hyper-Threading Vulnerability
Performance
¢ ZDnet: Hyperthreading hurts server performance, say developers
¢ ARM is no fan of HyperThreading
disadvantages
Hyper-Threading is not SMP. (Symmetric Multi-Processing)implies several processors, and we have only one processor. However, it is supplemented with a certain feature which lets it pretend it consists of two processors.
Well, the Hyper-Threading technology allows increasing efficiency of the processor in certain cases. In particular, when applications of different nature are used simultaneously. This is an advantage, but the effect takes place only in certain situations. The classical market principle says: pay more to get more.
It really boosts up performance sometimes. The effect can be much greater than even when we compare two platforms with the same processor but different chipsets. But the effect depends on a style of working with a computer. Note that the classical SMP style is when a user counts on the response of the classical multiprocessor system.
The style of the Hyper-Threading is a combination of entertaining or service processes with "working" processes. You won't get a tangible gain in most classical multiprocessor tasks if you run one application at a time. But you will surely make shorter the time of execution of most background tasks used as a makeweight. Intel has actually reminded us that operating systems we are using are multitask, and it offered a way to speed up fulfillment of a complex of simultaneously executed applications (not a single one). This is a very interesting approach, and we are glad this idea is realized.
for more please read
http://ixbtlabsarticles2/pentium43ghzht/
