CpE 442 Intro. To Computer Architecure

1. CpE 442 Intro. To Computer Architecure Review for Term Exam

2. The Role of Performance • Text3rd Edition, Chapter 4 • Main focus topics • Compare the performance of different architectures or architectural variations in executing a given application • Determine the CPI for an executable application on a given architecture • HW1 solutions, 2.11, 2.12, 2.13

3. Q2.13 [10] <§§2.2-2.3> Consider two different implementations, M1 and M2, of the same instruction set. There are three classes of instructions (A, B, and C) in the instruction set. M1 has a clock rate of 400 MHz, and M2 has a clock rate of 200 MHz. The average number of cycles per instruction (CPI) for each class of instruction on M1 and M2 is given in the following table: Class CPI on M1 CPI on M2 Instruction mix for C1 Instruction mix for C2 Instruction mix for C3 A 4 2 30% 30% 50% B 6 4 50% 20% 30% C 8 3 20% 50% 20% • Using C1 on both M1 and M2, how much faster can the makers of M1 claim that M1 is compared with M2? • ii. Using C2 on both M1 and M2, how much faster can the makers of M2 claim that M2 is compared with M1? • iii. If you purchase M1 which of the three compilers would you choose? • iv. If you purchase M2 which of the three compilers would you choose?

4. Sol. Using C1 compiler: M1: CPU Clock Cycles = 0.3*4+0.5*6+0.2*8 = 5.8 CPU time = CPU CC/Clock Rate = 5.8 / 400*10^6 = 0.0145*10^-6 M2: CPU CC = 3.2 CPU time = 3.2 / 200*10^6 = 0.016*10^-6 Thus, M1 is 0.016 / 0.0145 = 1.10 times as fast as M2. Using C2 compiler: Using the above method, M1: CPU time = 0.016*10^-6 M2: CPU time = 0.0145*10^-6 Thus, M2 is 0.016 / 0.0145 = 1.10 times as fast as M1. Using 3rd party: M1: CPU time = 0.0135*10^-6 M2: CPU time = 0.014*10^-6 Thus, M1 is 0.014 / 0.0135 = 1.04 times as fast as M2. The third-party compiler is the superior product regardless of machine purchase. M1 is the machine to purchase using the third-party compiler

5. The Instruction Set Architecure • Text, Ch. 2 • Compare instruction set architectures based on their complexity (instruction format, number of operands, addressing modes, operations supported) • Instruction set architecture types • Register-to-register • Register –to-memory • Memory –to-memory • HW2 solutions,

6. 2.51 Suppose we have made the following measurements of average CPI for instructions: Compute the effective CPI for MIPS. Average the instruction frequencies for SPEC2000int and SPEC2000fp in figure 2.48 to obtain the instruction mix. The effective CPI for MIPS is 1.125, this seems inaccurate because the table does not include the CPI for logical operations.

7. The Processor: Data Path and Control • Text, ch. 5 • The data path organization: functional units and their interconnections needed to support the instruction set. • The control unit design • Hardwired vs microprogramming design • HW3 and HW4,

10. The concept of the “critical path” , the longest possible path in the machine, was introduced in 5.4 on page 315. Based on your understanding of the single-cycle implementation, show which units can tolerate more delays (i.e. are not on the critical path), and which units can benefit from hardware optimization. Quantify your answers taking the same numbers presented on page 315. Longest path is load instruction (instruction memory, register file, ALU, data memory, register file). It can benefit by optimizing the hardware. Using the numbers from pg 315 Mem units: 200ps ALU&Adders: 100ps Register File: 50ps Critical path = 200+50+100+200+50 = 600ps (for lw) The path between the adders and the pc can tolerate more delays because they do not lie within the critical path. Any unit within the critical path (ALU, Register, Data memory) would benefit by optimizing the hardware, this would make the critical path shorter

11. IorD=0, (pc=pc+4 cont.) MemRead LDI

12. Micro-program for LDI

13. Pipelined Architecutres • Text, Ch.6 • Stages of a pipelined data path • Pipeline hazzards • Pipelined performance, number of cycles to execute a code segment (and the effective CPI), look for dependencies in sequencesinvolving lw and branch instructions (delay cyles) • HW5 6.22 lw $4, 100($2) sub $6, $4, $3 add $2, $3, $5 number of cycles = 5+2+1= 8 eff. CPI = 8/3 (n-1)+delay cycles #cycles / #instructions

14. The Memory Hierarchy • Text, Ch. 7 • The levels of memory hierarchy, and the principal of locality • Cache Design, direct-mapped, fully associative and set associative • Cache access, factors affecting the miss rate, and the miss penalty • Virtual memory, address map, page tables, and the TLB • HW6

15. 1 KB Direct Mapped Cache with 32 B Blocks 31 9 4 0 Cache Tag Example: 0x50 Cache Index Byte Select Ex: 0x01 Ex: 0x00 Stored as part of the cache “state” Valid Bit Cache Tag Cache Data : Byte 31 Byte 1 Byte 0 0 : 0x50 Byte 63 Byte 33 Byte 32 1 2 3 : : : : Byte 1023 Byte 992 31

16. And yet Another Extreme Example: Fully Associative 31 4 0 Cache Tag (27 bits long) Byte Select Ex: 0x01 Cache Tag Valid Bit Cache Data : X Byte 31 Byte 1 Byte 0 : X Byte 63 Byte 33 Byte 32 X X : : : X

17. Review:4-way setassociative

18. word ReadDirectMappedCache(address a) static Entry cache[CACHE_SIZE_IN_WORDS]; Entry e = cache[a.index] if (e.valid == FALSE || e.tag != a.tag) { e.valid = true; e.tag = a.tag; e.data = load_from_memory(a); } return e.data;  Modified to the following for multi-word blocks Problem  7.46 word ReadDirectMappedCache(address a) static Entry cache[CACHE_SIZE_IN_BLOCKS]; Entry e = cache[a.index] if (e.valid == FALSE || e.tag != a.tag) { e.valid = true; e.tag = a.tag; e.data = load_from_memory(a); }return e.data[a.word_index];