Describe how each of the following impacts Cache Performance: Cache Levels (L1, L2, L3) Replacement Policies (e.g., LRU vs Random) Cache Hit Latency
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L1 is the smallest and fastest cache, located closest to the CPU, followed by L2, which is larger but slightly slower, and L3, which is even larger and slower than L2. - The impact on cache performance is significant: L1 cache provides the fastest access times, Show more…
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Caching is used to serve stored data more efficiently. It is commonly used, particularly in large scale distributed systems, to allow the most frequently accessed information to be available at a lower cost in time or resources. Since cache capacity is limited, strategies are employed to determine what is in the cache and when it should be replaced. These are referred to as eviction policies and replacement policies. Which of the following are true? Pick ONE OR MORE options: A cache hit is a situation when the cache becomes full. LRU and MRU are eviction policies that respectively discard least recently used and most recently used elements from the cache to make space for other elements. In applications like social networks with feed, LRU, in general, performs significantly better than MRU. If the future is known, it is possible to design an eviction policy that is optimal. The data in a cache is always consistent with the changes made to it. Any time it is requested, the most recent version is returned.
Mauya M.
For the sequence of 32-bit memory word address references below: 0x03, 0xb4, 0x2b, 0x02, 0xbf, 0x58, 0xbe, 0x0e, 0xb5, 0x2c, 0xba, 0xfd a) Give the binary address, the tag, and the cache index and the offset for each reference assuming a 2-word block size and a 16-word cache. b) Which of the three direct-mapped cache designs below, all having a total of 8 words of data, would give the best performance? For all three design options, the cache is initially empty. • C1 has 1-word blocks • C2 has 2-word blocks • C3 has 4-word blocks To determine the design for best performance, calculate the miss rates and total cycles needed for the given sequence of memory references. For a hit, assume 1 cycle for a word transfer and one cycle per word in a cache block for tag matching. Hence, the number of cycles for a hit is 2, 3, and 5 for C1, C2, and C3 respectively. A cache miss amounts to 25 cycles. 2) By convention, cache sizes are given in terms of data/instruction storage capability, but caches also need to store tags and valid and dirty bits. For all parts, assume that the caches are byte addressable, and that addresses and words are 64 bits. a) i) Calculate the total number of bits required to implement a 32 kiB cache with two-word blocks. ii) Determine the ratio of bits required for tags, valid and dirty bits to the data storage bits. b) i) What is the total number of bits required for a 64 kiB cache with 16-word cache blocks, including tags, valid and dirty bits? ii) What is the ratio of the storage required for tags, valid and dirty bits to the data/instruction storage bits? iii) What is the ratio of the total number of bits required for the 64 kiB cache and the 32 kiB cache? 3) Assume the following for a memory system with L1 and L2 caches. L1: Write-through, no-write-allocate L2: Write-back, write-allocate a) i) Describe a scenario in which a buffer between L1 and L2 can improve performance and why. ii) Describe a scenario in which a buffer between L1 and L2 can improve performance and why. b) Describe the procedure for handling an L1 write-miss in terms of L1 and L2 actions.
Akash M.
2. A 2-way set associative cache system consists of 8 blocks. The main memory has 2048 blocks of 16 bytes each (byte addressable). The access time of the cache is 20 ns, and the time required to fill a cache block is 600 ns. Note that the method Load Through is used. Initially, the cache is empty. Assume that the least recently used (LRU) replacement algorithm is used. (a) Show the format of the memory address. (b) The computer will execute a program that loops 20 times from locations (addresses) 15 to 129. Complete Table 2 for the program executed for the first loop. (c) Compute the cache hit rate and the effective memory access time when running the program mentioned in Part (b).
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