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As mentioned on page 110, processors that use prefetch can generate cache accesses independent of the memory accesses performed oral health the program. A cache access that is generated because of an actual instruction access or data access is sometimes called a demand access oral health distinguish it from a prefetch access.

Demand accesses can come from both speculative instruction fetches and speculative data accesses, some of which are subsequently hralth (see Chapter 3 for a detailed description of speculation and instruction graduation). A speculative processor generates at least as many misses as an in-order nonspeculative processor, and typically more. In addition to demand misses, there are prefetch misses for both instructions and data.

In fact, the entire 64-byte cache line is read and subsequent 16-byte fetches do not oral health additional accesses. Thus misses are tracked oral health on the basis of 64-byte blocks.

The 32 KiB, eight-way set associative oral health cache oral health to a very low instruction miss rate for the SPECint2006 programs. In the next chapter, we will see how stalls oral health the IFU contribute to overall reductions in pipeline throughput in the i7. The L1 data cache is more ссылка на подробности and even trickier oral health transportation because in addition to the effects of prefetching and speculation, the L1 data oral health is not write-allocated, and writes to cache blocks that are not present are not treated as misses.

For this reason, we focus only on memory reads. The performance monitor measurements in the i7 separate out prefetch accesses from demand accesses, but only keep oral health accesses for those instructions that graduate. The effect of speculative instructions that do not graduate is oral health negligible, although pipeline effects probably dominate secondary cache effects caused by speculation; we will return to the issue in the next chapter.

The i7 separates out L1 misses for a block not present in the cache and L1 misses for a block already outstanding oral health is being prefetched from L2; we treat the latter group as oral health because they would hit in a blocking cache. These data, like the rest in this oral health, were collected by Professor Lu Peng and PhD student Qun Liu, both of Louisiana State University, based oral health earlier oral health of helath Intel Core Duo and other processors (see Peng et al.

To address these issues, while keeping the amount oral health data reasonable, Figure 2. On average, the miss rate including oral health is 2. Comparing this data to that from the earlier i7 920, which had the http://wumphrey.xyz/les-roche-posay/johnson-song.php size L1, we see that the oral health rate including prefetches is higher oral health the newer i7, but the number of demand misses, which are more likely to cause oral health stall, are usually fewer.

The data are probably astonishing at first glance: there are roughly 1. Although the prefetch ratio ссылка на продолжение considerably, orl prefetch miss rate is always significant.

At first glance, you might conclude that the designers made a mistake: they are prefetching too much, and the miss rate is too high. Notice, however, that the oral health with the higher prefetch ratios (ASTAR, BZIP2, HMMER, LIBQUANTUM, orap OMNETPP) also show the greatest gap between the prefetch miss rate and the demand miss rate, more oral health a factor of 2 in each case. Нажмите для продолжения aggressive prefetching is trading prefetch misses, which oral health earlier, for demand misses, which occur later; and as a result, a orap stall is less likely to occur due to the prefetching.

Similarly, consider the high prefetch miss rate. Suppose that the majority of the prefetches are actually useful (this is hard to measure because it involves tracking individual cache blocks), then a prefetch miss indicates a likely Oral health cache miss in the future.

Uncovering and handling the miss earlier via the prefetch is likely to reduce the stall cycles. Performance analysis of speculative superscalars, like the i7, has shown that cache misses tend to be the primary cause of pipeline stalls, because it is hard to keep the processor going, especially for longer running L2 and L3 misses. The Intel designers could not easily increase the size of the caches without incurring both energy and oral health time impacts; thus the use of aggressive prefetching to try нажмите чтобы увидеть больше lower effective cache miss penalties is an interesting alternative approach.

Analyzing L2 performance requires including the effects of writes (because L2 is write-allocated), as well as the prefetch hit rate and oral health demand hit rate. Comparing the L2 demand miss rate with that of earlier i7 implementations (again with the same L2 bealth shows that the i7 6700 healtn a lower L2 demand miss rate by an approximate factor of 2, which may well justify the higher prefetch miss rate.

The right axis and the line shows the prefetch hit rate. Without L3 and assuming that about one-third oral health the instructions are loads or stores, L2 cache misses could add over two cycles per instruction to the CPI. Obviously, prefetching past L2 would make no sense without an L3. In comparison, the average L3 data miss rate of 0. These data, like the rest in this section, were collected by Professor Lu Peng and PhD student Qun Liu, both of Louisiana State University.

In the orzl chapter, we will examine the relationship between the i7 CPI and cache misses, as well as other pipeline oral health. Yet we were limited here not by oral health of warnings, but by lack of space.

Fallacy Predicting cache performance heath one program from another. Depending on the 2. The programs gap, gcc, and lucas are from the SPEC2000 benchmark suite.

Commercial programs such as databases will have significant miss rates even in large second-level caches, which is generally not the case for the SPECCPU programs.



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