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traditional microprocessor can more easily run legacy code, which may then be accelerated by cache control instructions, whilst a scratchpad based machine requires dedicated coding from the ground up to even function. Cache control instructions are specific to a certain cache line size, which in practice may vary between generations of processors in the same architectural family. Caches may also help coalescing reads and writes from less predictable access patterns (e.g., during
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devote more transistors to accelerating code written in traditional languages, e.g., performing automatic prefetch, with hardware to detect linear access patterns on the fly. However the techniques may remain valid for throughput-oriented processors, which have a different throughput vs latency
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The disadvantage is it requires significantly different programming techniques to use. It is very hard to adapt programs written in traditional languages such as C and C++ which present the programmer with a uniform view of a large address space (which is an illusion simulated by caches). A
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This hint is used to discard cache lines, without committing their contents to main memory. Care is needed since incorrect results are possible. Unlike other cache hints, the semantics of the program are significantly modified. This is used in conjunction with
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instruction set, which suggests that data will only be used once, i.e., the cache line in question may be pushed to the head of the eviction queue, whilst keeping it in use if still directly needed.
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to achieve high throughput whilst working around memory latency (reducing the need for prefetching). Many read operations are issued in parallel, for subsequent invocations of a
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This hint requests the immediate eviction of a cache line, making way for future allocations. It is used when it is known that data is no longer part of the
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This hint is used to prepare cache lines before overwriting the contents completely. In this example, the CPU needn't load anything from
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In recent times, cache control instructions have become less popular as increasingly advanced application processor designs from
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As such scratchpads are generally harder to use with traditional programming models, although
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for managing temporary data. This saves unneeded main memory bandwidth and cache pollution.
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Several such instructions, with variants, are supported by several processor
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The disadvantage is that many copies of temporary states may be held in the
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of a cache-line sized block to zero, but the operation is effectively free.
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of memory access, for example in a loop traversing memory linearly. The
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tradeoff, and may prefer to devote more area to execution units.
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should occur sufficiently far ahead in time to mitigate the
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instruction set. Some variants bypass higher levels of the
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442:"Power PC manual, see 1.10.3 Cache Control Instructions"
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can be used to invoke this in the programming languages
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244:A variant of prefetch for the instruction cache.
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297:that also imply cache hints. An example is
347:when needed. This approach is used by the
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106:Learn how and when to remove this message
339:into which temporaries may be put, and
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134:intended to improve the performance of
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293:Some processors support a variant of
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44:adding citations to reliable sources
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395:graphics processing unit
335:Some processors support
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170:architectures, such as
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479:Computer architecture
140:memory access pattern
393:(for example modern
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240:Instruction prefetch
40:improve this article
202:instruction in the
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314:Automatic prefetch
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331:Scratchpad memory
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96:September 2016
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38:Please help
33:verification
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403:parallelism
397:(GPUs) and
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289:Other hints
283:working set
254:main memory
156:working set
128:instruction
458:2016-06-11
428:References
380:TensorFlow
144:programmer
66:newspapers
363:machine.
299:load last
132:processor
120:computing
473:Category
399:Xeon Phi
376:dataflow
361:manycore
212:prefetch
200:PREFETCH
190:Prefetch
162:Examples
148:compiler
303:PowerPC
301:in the
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180:PowerPC
80:scholar
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182:, and
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452:(PDF)
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420:of a
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320:Intel
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324:ARM
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