Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3)...

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Lecture Objectives: Cache Basics 1) Define temporal and spatial locality. 2) Define hit rate and miss rate. 3) Define the term cache 4) Explain how a direct mapped cache determines the location in the cache. 5) Given a memory address and cache size information, perform the calculations to convert an address to a cache block number.

Transcript of Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3)...

Page 1: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Lecture Objectives:

Cache Basics

1) Define temporal and spatial locality. 2) Define hit rate and miss rate.3) Define the term cache 4) Explain how a direct mapped cache determines the location in the cache. 5) Given a memory address and cache size information, perform the calculations to convert an

address to a cache block number.

Page 2: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Memory access time - exercise

• Recall: The MEM stage of the MIPS pipeline takes 200ps.– Is it actually possible to request and retrieve (i.e.

make a round trip) a word of memory in that period of time (assume that the memory chip is 60mm away from the CPU)?

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Page 3: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Definitions

• Temporal Locality– The principle stating that if a data location is

referenced then it will again be referenced soon.

• Spatial Locality– The locality principle stating that if a data location

is referenced, data locations with nearby addresses will tend to be referenced soon.

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Page 4: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Computer memory hierarchy

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Page 5: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

SYX SG-125 Gaming PC• Intel Core i7 2600 3.4 GHz,

Genuine Windows® 7 Professional 64 Bit, 1GB NVIDIA GeForce GTX 550 Ti, 8GB DDR3, 1TB 7200rpm HDD, Blu-Ray, USB 3.0

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Page 6: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Definitions

• Block– The minimum unit of information that can be either

present or not present in the cache

• Hit Rate– The fraction of memory accesses found in the level of the

memory hierarchy

• Miss Rate– The fraction of memory accesses not found in a level of the

memory hierarchy

• Miss penalty– The time required to fetch a block into a level of memory

hierarchy from the lower level.CS2710 Computer Organization 6

Page 7: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Cache Memory

• The level of memory closest to the Processor

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Page 8: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Determining where to look

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(Block Address) mod(Number of Blocks In Cache)

Block to access Cache Location (16 blocks)0x01

0x05

0x15

0x22

0x37

0x3F

0x3D

Page 9: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Direct Mapped Cache #Blocks is a power of 2 Use low-order address bits

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Page 10: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Tags and Valid bits

• If we search the cache, how do we know if the data is valid or not?

• How do we know which specific block in in the cache?

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Page 11: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Example Address stream

• 10110, 11010, 10000, 10110, 00011, 10010,

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Index V Tag Data

000 N

001 N

010 N

011 N

100 N

101 N

110 N

111 N

Page 12: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Address Subdivision

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Page 13: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Determining Sizes

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2

( 2)

2

2 (2 )

n

m m

TagFieldSize AddressBusSize n m

CacheSize Blocks

BlockSize Words bytes

Page 14: Lecture Objectives: 1)Define temporal and spatial locality. 2)Define hit rate and miss rate. 3) Define the term cache 4)Explain how a direct mapped cache.

Minute Quiz

• Which of the following statements is generally false?A. Caches primarily take advantage of temporal

localityB. On a read, the value returned depends upon

which blocks are in the cacheC. Most of the capacity of the memory hierarchy is

at the lowest levelD. The most expensive portion of the memory

hierarchy is at the highest level

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