04 cache organization 18 24 tủ tài liệu bách khoa

The cache might get confused later!. And how do we solve that?... m-bit Address k bits m-k-n bits n-bit Block Offset Tag Index 4-bit Address?. bits?. bits ?-bits Block Offset block..

¢  

¢  

¢  

¢  

¢  

Where should we put data in the cache?

00

01

10

11

Index

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

Data

¢  How can we compute this mapping?

Where should we put data in the cache?

00

01

10

11

Index

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

Data

Hmm The cache might get confused later! Why? And how do we solve that?

01

10

11

Index

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

Tag Data

00

??

01

01

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Byte

Address

0

1

2

3

Index

0

1

2

3

4

5

6

7

Block (line) number

¢  

¢  

¢  

¢  

Problems with direct mapped caches?

program uses addresses

00

01

10

11 Index

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111 Memory Address

¢  

¢  

0

1

2

3

4

5

6

7

Set

0

1

2

3

Set

0

1

Set

1-way

8 sets,

1 block each

2-way

4 sets,

2 blocks each

4-way

2 sets,

4 blocks each

0

Set

8-way

1 set,

8 blocks

m-bit Address

k bits (m-k-n) bits

n-bit Block Offset Tag Index

4-bit Address

? bits

? bits

?-bits Block Offset

block Where would 13 (1101) be stored?

Example placement in set-associative caches

¢   0x1833in binary is 00 0110000 011 0011

0

1

2

3

4

5

6

7

Set

0

1

2

3

Set

0

1

Set

1-way associativity

8 sets, 1 block each 4 sets, 2 blocks each 2-way associativity 2 sets, 4 blocks each 4-way associativity

m-bit Address

k bits (m-k-n) bits

n-bit Block Offset Tag Index

Example placement in set-associative caches

¢   0x1833in binary is 00 0110000 011 0011

m-bit Address

k bits (m-k-4) bits

4-bit Block Offset Tag Index

0

1

2

3

4

5

6

7

Set

0

1

2

3

Set

0

1

Set 1-way associativity

8 sets, 1 block each 4 sets, 2 blocks each 2-way associativity 2 sets, 4 blocks each 4-way associativity

Block replacement

¢   Any empty block in the correct set may be used for storing data

¢   Replace something, of course, but what?

0

1

2

3

4

5

6

7

Set

0

1

2

3

Set

0

1

Set 1-way associativity

8 sets, 1 block each 4 sets, 2 blocks each 2-way associativity 2 sets, 4 blocks each 4-way associativity

¢  

¢  

¢  

¢