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A barrel processor is a CPU that switches between threads of execution on every cycle. This CPU design technique is also known as "interleaved" or "fine-grained" multithreading. CPU redirects here. ...
A thread in computer science is short for a thread of execution. ...
The instruction cycle is the time period during which one instruction is fetched from memory and executed when a computer is given an instruction in machine language. ...
A CPU generally has these components: Datapaths (such as ALUs and pipelines) Logic which controls the datapaths memory components such as register files, caches clock circuitry such as clock drivers, PLLs, clock distribution networks pad transceivers circuitry logic gate cell library which is used to implement the logic CPUs designed...
For example, certain CDC Cyber computers executed one instruction from each of 20 different threads before returning to the first thread. Also, the IP3023 processor from Ubicom executes one instruction from each of 8 different threads before returning to the first thread. The Cyber range of mainframe computers were Control Data Corporations primary products during the 1970s and 1980s. ...
In computer science, an instruction typically refers to a single operation of a processor within a computer architecture. ...
Ubicom is a prominent supplier of software and communication processor platforms. ...
Like preemptive multitasking, each thread of execution is assigned its own program counter and other registers (each thread's architectural state). However, a barrel processor can guarantee that each thread will get to execute 1 instruction every N cycles. In contrast, a preemptive multitasking machine typically runs one thread of execution for hundreds or thousands of cycles while all other threads wait their turn. Pre-emptive multitasking is a form of multitasking in which processes are not allowed to take an indefinitely long time to complete execution in the CPU. Each process, in turn, is granted a portion of CPU time (usually called a time slice, on the order of milliseconds). ...
The program counter (also called the instruction pointer in some computers) is a register in a computer processor which indicates where the computer is in its instruction sequence. ...
The architectural state is the part of the CPU which holds the state of a process, this includes: general purpose registers (as in AX,BX,CX... in a 80x86 processor). ...
Pre-emptive multitasking is a form of multitasking in which processes are not allowed to take an indefinitely long time to complete execution in the CPU. Each process, in turn, is granted a portion of CPU time (usually called a time slice, on the order of milliseconds). ...
A technique called C-slowing can take a normal single-tasking processor design and automatically generate a corresponding barrel processor design. An n-way barrel processor generated this way acts much like n separate multiprocessing copies of the original single-tasking processor, each one running at roughly 1/n the original speed. C-slowing is a technique used in FPGA circuits to improve throughput. ...
Multiprocessing is traditionally known as the use of multiple concurrent processes in a system as opposed to a single process at any one instant. ...
Advantages A single-tasking processor spends a lot of time waiting around, not doing anything useful, whenever a cache miss or pipeline stall occurs. Advantages to employing barrel processors over single-tasking processors include: This article is about the computer term. ...
In computer architecture, a hazard is a potential problem that can happen in a pipelined processor. ...
- they can do useful work on the other threads while the stalled thread is waiting.
- n-way barrel processors with n-deep pipelines are much simpler than single-tasking processors because they never have a pipeline stall and don't need feed-forward circuits.
Barrel processors have many advantages over single-tasking processors in real-time applications, because they can guarantee that a "real-time" thread can execute with precise timing, no matter what happens to the other threads -- even if some other thread locks up in an infinite loop or is continuously interrupted by hardware interrupts. In computer architecture, a hazard is a potential problem that can happen in a pipelined processor. ...
Feed-forward is a term describing a kind of system which reacts to changes in its environment, usually to maintain some desired state of the system. ...
Wikipedia does not have an article with this exact name. ...
A deadlock is a situation wherein two or more competing actions are waiting for the other to finish, and thus neither ever does. ...
An infinite loop is a sequence of instructions in a computer program which loops endlessly. ...
In computer engineering, an interrupt is a signal from a device which typically results in a context switch: that is, the processor sets aside what its doing and does something else. ...
Disadvantages There are, however, some disadvantages to barrel processors. All the threads must share the same cache, which can slow overall performance. This can especially slow down tasks which require low latency and depend heavily on cache memory. In addition, if there are insufficient threads available to run, a barrel processor may not have anything useful to do during a stall. Diagram of a CPU memory cache A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. ...
Low latency allows human-unnoticeable delays between an input being processed and the corresponding output providing real time characteristics. ...
See also
Super-threading is a form of simultaneous multithreading, similar in design to hyper-threading. ...
In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is...
Simultaneous multithreading, often abbreviated as SMT, is a technique for improving the overall efficiency of the hardware that executes instructions in a computer. ...
Hyper-Threading (HTT = Hyper Threading Technology) is Intels trademark for their implementation of the simultaneous multithreading technology on the Pentium 4 microarchitecture. ...
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