1. II. A new era in processor evolution Dezső Sima Spring 2007 (Ver. 2.0)  Dezső Sima, 2007

2. Foreword Beginning with second generation superscalars, the continuous, approximately 10-fold- per-decade increase of processor efficiency leveled off for reasons shown in Chapter I. Designers responded by massively rising clock frequencies at up to a 100-fold-per- decade rate in order to sustain an approximately 100-fold-per-decade performance increase. Such a rapid progress, however inevitably encountered its limits due to declining processor efficiency, increasing dissipation and skew in parallel buses, as shown in this Chapter. As a consequence, a decade long era of processor evolution, characterized by massively rising clock frequencies, ended in the last few years. The new era is heralded by multicore and multithreaded designs, as discussed in Chapters III. and IV.

3. Contents 1. Processor performance 2. Efficiency of processors 3. Addressing the leveling off of processor efficiency 4. Aggressively raising clock frequency 5. The efficiency wall 6. The thermal wall 7. The skew wall 8. EPIC architectures/processors 9. The end of an era in processor evolution

4. 1. Processor Performance

5. Relative performance Absolute performance Number of succesfully executed instructions/sec Number of succesfully executed operations/sec (SIMD) Relating the execution times of a benchmark program on the tested system to a reference system according to the following interpretation: E.g.: SPECint92, SPECint_base2000 1.1. Introduction (1) f c : Clock frequency IPC: Instructions/cycle OPI: Operations/cycle

6. 1.1. Introduction (2) In general purpose applications: where: IPC: issued instructions per cycle η: number of successfully executed/issued instructions (efficiency of the speculative execution)

7. In performance/efficiency studies: Theoretical interpretation: P a Practical measurement: P r 1.1. Introduction (3) ?

8. If the following were true: In that case: 1.1. Introduction (4) I: Number of instructions in the application considered

9. However: Figure 1.1.: Runtime ratios of the component programs of SPECint2000 Source: http://www.spec.org 1.1. Introduction (5)

10. When comparing the performance of two systems: This estimation is useable in trend considerations. 1.1. Introduction (6)

11. Comparing the efficiency of two systems: 1.1. Introduction (7)

12. 1.2. Evolution of processor performance (1) Figure 1.2: Integer performance growth of Intel’s x86 processors

13. Figure 1.3: Integer performance growth (in general - 1) Source: X86-64 Technology White Paper, AMD Inc., Sunnyvale, CA, 2000 1.2. Evolution of processor performance (2)

14. 3. Figure 1.4: Integer performance growth (in general - 2) Source: F. Labonte, www-vlsi.stanford.edu/group/chart/specInf2000.pdf 1.2. Evolution of processor performance (3)

15. 2. Efficiency of processors

16. 2.1. Introduction ?

17. Figure 2.1: Efficiency of Intel processors 2.2. Growth of processor efficiency (1)

18. Figure 2.2: Growth of processor performance/efficiency (in general) Source: J. Birnbaum, „Architecture at HP: Two decades of Innovation”, Microprocessor Forum, October 14, 1997. 2.2. Growth of processor efficiency (2)

19. 2.3. Contribution of raising processor efficiency to the growth of processor performance (up to the 2 nd generation of superscalars) A második generációig az órafrekvencia és a hatékonyság növelése egyenlő arányban járultak hozzá a teljesítmény növeléséhez. ?

20. 2.4. Sources of raising processor efficiency Increasing the word length Introducing and increasing temporal parallelism Introducing and increasing issue parallelism 8/16  32 bit (286  386DX) 1 st and 2 nd generation pipeline processors (386DX, 486DX) 1 st and 2 nd generation superscalars (Pentium, Pentium Pro)

21. 2.5. Limit of raising processor efficiency (1) Processing width 4 RISC instructions/cycle ~3 CISC instructions/cycle Figure 2.3: Processing width of 2 nd generation (wide) superscalars vs extent of parallelism available in general purpose applications 2 nd generation superscalars (wide superscalars) Source: Wall: Limits of ILP, WRL TN-15, Dec. 1990

22. Figure 2.4: Growth of processor efficiency (in general) 2.5. Limit of raising processor efficiency (2)

23. 2.5. Limit of raising processor efficiency (3) Beginning with 2 nd generation (wide) superscalars the sources of extensively raising processor efficiency became exhausted In general purpose applications: The width of 2 nd generation superscalars already approaches the extent of available parallelism (ILP)

24. 3. Addressing the leveling off of processor efficiency

25. Essentially widening the core by introducing EPIC architectures Aggresively raising clock frequency Main road of evolution (Sections 4 – 7)(Section 8)

26. 4. Aggressively raising clock frequency

27. By reducing the logic depth of pipline stages By scaling down the feature size in the manufacturing process 4.1. Sources of raising clock frequencies (1) Raising clock frequency

28. Figure 4.1: Evolution of Intel’s process technology Source: D. Bhandarkar: „The Dawn of a New Era”, 11. EMEA, May, 2006. 4.1. Sources of raising clock frequencies (2)

29. 20 30 Year * 10 40 1990 2000 * * * * Pentium (5) 2005 No of pipeline stages Pentium Pro (~12) Pentium 4 (~20) Athlon-64 (12) P4 Prescott (~30) (14) Conroe * Athlon (6) K6 (6) * 1995 * Core Duo Figure 4.2: Number of pipeline stages in Intel’s and AMD’s processors 4.1. Sources of raising clock frequencies (3)

30. Figure 4.3: Max. logic depth of pipeline stages in processors (in terms of FO4) Source: F. Labonte www-vlsi.stanford.edu/group/chart/CycleFO4.pdf 4.1. Sources of raising clock frequencies (4)

31. Figure 4.4: Growth of clock frequencies in Intel’s x86 line of processors 4.2. Growth rate of clock frequencies (1)

32. Figure 4.5: Growth of clock frequencies (in general) 4.2. Growth rate of clock frequencies (2)

33. Emerging limits of evolution Ousting of major RISC families 4.3. Implications of aggressively raising clock frequencies 4.3.1 Overview (4.3.2) (4.3.3)

34. Figure 4.6: The shift in performace leadership between RISC and x86 lines 4.3.2. Ousting of major RISC families (2)

35. 1995-2000: CISCs overtook the performance leadership then it is a more intrinsic task to raise f c from a higher value than from a lower one in the same rate 1997: Intel and HP unveiled IA-64/Merced as the next generation architecture/processor line Cancelling of most major RISC lines, such as MIPS’s R-Lines, HP’s Alpha and PA lines, PowerPC Consortium’s PowerPC line 4.3.2. Ousting of major RISC families (2)

36. 4.3.3. Emerging limits of evolution The skew wall The thermal wall The efficiency wall (Section 5) (Section 6) (Section 7)

37. 5. The efficiency wall

38. speed gap between the processor and the memory 5.1. Overview Basic reason: (widens on higher frequencies)

39. Memory transfer rates DRAM latencies Transfer rates of processor buses L2 cache latencies Main appearances of the speed gap between the processor and the memory: 5.1. Overview (2)

40. 5.2. Speed gap between processor and memory (1) Figure 5.1: Latency of DRAM chips (in clock cycles)

41. Figure 5.2: Relative transfer rate of memories (D: dual channel) 5.2. Speed gap between processor and memory (2)

42. f c max at intro. (GHz) L2 size (Kbyte) L2 latency (clock cycles) Willamette1.5 128 7 Northwood2.0 51216 Prescott3.4 102423 Figure 5.3: Latency of L2 caches 5.2. Speed gap between processor and memory (3)

43. Figure 5.4: Relative transfer rates of processor buses 5.2. Speed gap between processor and memory (4)

44. 5.3. Efficiency of 3 rd generation superscalars (1) 5.5: Efficiency of Intel’s Pentium III and Pentium 4 processors in general purpose applications

45. Figure 5.6: efficiency of AMD’s Athlon, Athlon XP and Athlon 64 processors in general purpose applications 5.3. Efficiency of 3 rd generation superscalars (2)

46. Figure 5.7: Main aspects of the memory subsystem affecting core efficiency 5.3. Efficiency of 3 rd generation superscalars (3)

47. Figure 5.8: Contrasting the efficiency of Intel’s and AMD’s processors 5.3. Efficiency of 3 rd generation superscalars (4)

48. Figure 5.9: Contrasting Intel’s and AMD’s processor design philosophies 5.3. Efficiency of 3 rd generation superscalars (5)

49. Diminishing return on higher clock frequencies Implication of the emerging efficiency wall: 5.3. Efficiency of 3 rd generation superscalars (6)

50. 6. The thermal wall

51. 6. The thermal wall (1) Dissipation (D) : D d =A*C*V 2 *f c with A:ratio of the active gates C:effective capacity of the gates V:supply voltage f c :clock frequency I leak :leakage current Dynamic Static D s =V*I leak

52. 6. The thermal wall (2) Figure 6.1:Chip dynamic and static power dissipation trends Source: N. S. Kim et al., „Leakage Current: Moore’s Law Meets Static Power”, Computer, Dec. 2003, pp. 68-75.

53. Source:Solie D., „Technology Trends, Aug. 2006, http://www-03.ibm.com/procurement/proweb.nsf/objectdocswebview/http://www-03.ibm.com/procurement/proweb.nsf/objectdocswebview/ file14+-+darryl+solie+-+ibm+power+symposium+presentation/file14+-+darryl+solie+-+ibm+power+symposium+presentation/$file/14+-+darryl+solie-ibm-power+symposium+presentation+v2.pdf Figure 6.2: Dynamic and static power dissipation trends

54. Figure 6.3: Relative dissipation of Intel’s x86 family of processors 6. The thermal wall (3)

55. Figure 6.4: Contrasting the evolution of Intel’s and AMD’s processor lines with the thermal wall 6. The thermal wall (4)

56. Figure 6.5: Intel’s P4 processor family (Netburst architecture) 6. The thermal wall (5)

57. Figure 6.6: The growth of relative dissipation of processors (in general) Source: R Hetherington, „The UltraSPARC T1 Processor” White Paper, Sun Inc., 2005 6. The thermal wall (6)

58. Implications of the thermal wall: 6. The thermal wall (7) Processor designs focus now more and more on power aware technics The approach to increase performance by aggressively raising clock frequency met the thermal wall

59. 7. The skew wall

60. Reason: Figure 7.1: Skew between lines of parallel buses 7. The skew wall (1)

61. Figure 7.2: Equalizing skews among different bit lines of the processor bus on the MSI 915G Combo motherboard 7. The skew wall (2)

62. 7. The skew wall (3) Introducing sequential buses Figure 7.3: Signal transfer over a sequential bus (also in slow peripheral buses due to impressive cost savings) Implication of emerging skews between bit lines of parallel buses:

63. Implication of emerging limits of evolution The approach to aggressively raise clock frequencies met the efficiency, thermal and skew walls and thus hit the dead end

64. 8. EPIC architectures/processors

65. 8. EPIC architectures/processors (1) Essentially widening the core by introducing EPIC architectures Aggresively raising clock frequency Main road of evolution (Sections 4 – 7)(Section 8)

66. Instructions Principle of superscalar processing FEFE FEFE FEFE dynamic dependency resolution Processor dependent instructions Principle of VLIW processing FEFE FEFE FEFE VLIW: Very Large Instruction Word independent instructions (static dependency resolution) Processor Figure 8.1: Contrasting the principles of operation of superscalar and VLIW processors 8. EPIC architectures/processors (2)

67. VLIWEPIC EPIC: Explicitly Parallel Instruction Computer enhanced VLIW branch prediction explicit cache control (integration of advanced superscalar features) 8. EPIC architectures/processors (3) 1994: Intel, HP 2001: IA-64  Itanium 1997:EPIC designation

68. Figure 8.2: Overview of Itanium cores 8. EPIC architectures/processors (4)

69. Figure 8.3: The efficiency of Itanium processors 8. EPIC architectures/processors (5)

70. Figure 8.4: Expected spreading of the IA-64 architecture (Itanium processors) Source: L. Gwennap: Intel’s Itanium and IA-64: Technology and Market Forecast, MDR, 2000 8. EPIC architectures/processors (6)

71. Figure 8.5: Revenue expectations concerning Intel’s Itanium line 8. EPIC architectures/processors (7)

72. In general purpose applications: EPIC architectures/processors play a decreasing role 8. EPIC architectures/processors (8)

73. 9. The end of an era in processor evolution

74. 9. The end of an era in processor evolution (1) In general purpose applications beginning with the 2. generation superscalars processor efficiency leveled off, but both approaches to address leveling off efficiency met limits of evolution and thus hit the dead end Single core complex superscalars, – at the end of an era

75. 9. The end of an era in processor evolution (2) A new era in processor evolution – The dawn of multicore, multithreded processors The number of processors will double also in each ~ 24 months Available hardware complexity increases further on exponentially (Moore’s law) Complexity is doubled in each ~ 24 moths

76. Figure 9.1: Rapid spreading of multi core processors revealed by Intel 9. The end of an era in processor evolution (3)