Slipstream (computer science)
Encyclopedia
A slipstream processor is an architecture designed to reduce the length of a running program by removing the non-essential instructions.
It is a form of speculative computing
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Non-essential instructions include such things as results that are not written to memory, or compare operations that will always return true. Also as statistically most branch instructions will be taken it makes sense to assume this will always be the case.
Because of the speculation involved slipstream processors are generally described as having two parallel executing streams. One is an optimized faster A-stream executing the reduced code, the other is the slower R-stream which runs behind the A-stream and executes the full code. The R-stream runs faster than if it were a single stream due to data being prefetched
by the A-stream effectively hiding memory latency. The two streams both complete faster than a single stream would. As of 2005, theoretical studies have shown that this configuration can lead to a speedup of around 20%.
The main problem with this approach is accuracy: As the A-stream becomes more accurate and less speculative, the overall system runs slower. Furthermore, a large enough distance is needed between the A-stream and the R-stream so that cache misses generated by the A-stream do not slow down the R-stream.
It is a form of speculative computing
Speculative execution
Speculative execution in computer systems is doing work, the result of which may not be needed. This performance optimization technique is used in pipelined processors and other systems.-Main idea:...
.
Non-essential instructions include such things as results that are not written to memory, or compare operations that will always return true. Also as statistically most branch instructions will be taken it makes sense to assume this will always be the case.
Because of the speculation involved slipstream processors are generally described as having two parallel executing streams. One is an optimized faster A-stream executing the reduced code, the other is the slower R-stream which runs behind the A-stream and executes the full code. The R-stream runs faster than if it were a single stream due to data being prefetched
Prefetching
Prefetching may refer to:* Instruction prefetch, in computer architecture, a microprocessor speedup technique* Prefetch input queue , in computer architecture, pre-loading machine code from memory...
by the A-stream effectively hiding memory latency. The two streams both complete faster than a single stream would. As of 2005, theoretical studies have shown that this configuration can lead to a speedup of around 20%.
The main problem with this approach is accuracy: As the A-stream becomes more accurate and less speculative, the overall system runs slower. Furthermore, a large enough distance is needed between the A-stream and the R-stream so that cache misses generated by the A-stream do not slow down the R-stream.