Data-centric Metaprogramming @ EcoCloud 2015

Data-centric metaprogramming at the annual EcoCloud gathering 2015, Lausanne, Switzerland Website: http://www.ecocloud.ch/

Project website: http://scala-ildl.org

1. scala-ildl.org Language and Compiler Support for Custom Data-centric Optimizations
2. scala-ildl.org Vlad URECHE PhD student in the Scala Team @ EPFL Working on program transformations in the Scala programming language, focusing on data representation. @ @VladUreche @VladUreche vlad.ureche@epfl.ch
3. scala-ildl.org Language and Compiler Support for Custom Data-centric Optimizations
4. scala-ildl.org • written by the programmer in the host language Language and Compiler Support for Custom Data-centric Optimizations
5. scala-ildl.org • targering the data: representation and operations Language and Compiler Support for Custom Data-centric Optimizations
6. scala-ildl.org • performance • latency • memory footprint • energy footprint Language and Compiler Support for Custom Data-centric Optimizations
7. scala-ildl.org across general-purpose libraries Language and Compiler Support for Custom Data-centric Optimizations
8. scala-ildl.org Motivation Data-centric Optimizations Conclusion Applications
9. scala-ildl.org Data Representation Challenge Data Representation Challenge class Vector[T] { … }
10. scala-ildl.org Data Representation Challenge Data Representation Challenge class Vector[T] { … } The Vector collection in the Scala library
11. scala-ildl.org Data Representation Challenge Data Representation Challenge case class Employee(...) ID NAME SALARY class Vector[T] { … } The Vector collection in the Scala library
12. scala-ildl.org Data Representation Challenge Data Representation Challenge case class Employee(...) ID NAME SALARY Auto-generated, corresponds to a table row class Vector[T] { … } The Vector collection in the Scala library
13. scala-ildl.org Data Representation Challenge Data Representation Challenge case class Employee(...) ID NAME SALARY Auto-generated, corresponds to a table row class Vector[T] { … } The Vector collection in the Scala library
14. scala-ildl.org Data Representation Challenge Data Representation Challenge class Vector[T] { … } case class Employee(...) ID NAME SALARY
15. scala-ildl.org Data Representation Challenge Data Representation Challenge class Vector[T] { … } case class Employee(...) ID NAME SALARY
16. scala-ildl.org Data Representation Challenge Data Representation Challenge case class Employee(...) ID NAME SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY class Vector[T] { … }
17. scala-ildl.org Data Representation Challenge Data Representation Challenge case class Employee(...) ID NAME SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY class Vector[T] { … } Traversal requires dereferencing a pointer for each employee.
18. scala-ildl.org A Better Representation A Better Representation Vector[Employee] ID NAME SALARY ID NAME SALARY
19. scala-ildl.org A Better Representation A Better Representation NAME ... NAME VectorOfEmployee ID ID ... ... SALARY SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY 5x faster
20. scala-ildl.org A Better Representation A Better Representation • Individually, Vector[T] and Employee can't be optimized • Together, Vector[Employee] can be optimized NAME ... NAME VectorOfEmployee ID ID ... ... SALARY SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY 5x faster
21. scala-ildl.org A Better Representation A Better Representation • Individually, Vector[T] and Employee can't be optimized • Together, Vector[Employee] can be optimized NAME ... NAME VectorOfEmployee ID ID ... ... SALARY SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY 5x faster Current challenge: No means of communicating this to the compiler
22. scala-ildl.org
23. scala-ildl.org • Transforming the code by hand – Loses high-level intent – Changes ripple outside
24. scala-ildl.org • Transforming the code by hand – Loses high-level intent – Changes ripple outside Can we automate this?
25. scala-ildl.org Motivation Data-centric Optimizations Conclusion Applications
26. scala-ildl.org Data-centric Optimzations Data-centric Optimzations • Optimization rules – written in the host language – entry point: data (targeted via types) – changes: data representation and operations
27. scala-ildl.org Data-centric Optimzations Data-centric Optimzations • Optimization rules – written in the host language – entry point: data (targeted via types) – changes: data representation and operations object VectorOfEmployeeSoA extends Transformation { type Target = Vector[Employee] type Result = VectorOfEmployee // conversions, operations, ... }
28. scala-ildl.org Why Does it Matter? Why Does it Matter?
29. scala-ildl.org Transformation Transformation Definition Application
30. scala-ildl.org Transformation Transformation Definition Application • can't be automated • based on experience • based on speculation • one-time effort
31. scala-ildl.org Transformation Transformation Definition Application • can't be automated • based on experience • based on speculation • one-time effort • repetitive and simple • affects code readability • is verbose • is error-prone
32. scala-ildl.org Transformation Transformation programmer Definition Application • can't be automated • based on experience • based on speculation • one-time effort • repetitive and simple • affects code readability • is verbose • is error-prone compiler (automated)
33. scala-ildl.org
34. scala-ildl.org Is that all? Is that all?
35. scala-ildl.org Diversity Diversity Vector[Employee] ID NAME SALARY ID NAME SALARY
36. scala-ildl.org Diversity Diversity NAME ... NAME VectorOfEmployee ID ID ... ... SALARY SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY
37. scala-ildl.org Diversity Diversity NAME ... NAME VectorOfEmployee ID ID ... ... SALARY SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY VectorOfEmployeeJSON { id: 123, name: “John Doe” salary: 100 }
38. scala-ildl.org Diversity Diversity NAME ... NAME VectorOfEmployee ID ID ... ... SALARY SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY VectorOfEmployeeJSON { id: 123, name: “John Doe” salary: 100 } CompactVector <compressed binary blob>
39. scala-ildl.org Scopes Scopes def indexSalary(employees: Vector[Employee], by: Float): Vector[Employee] = for (employee ← employees) yield employee.copy( salary = (1 + by) * employee.salary )
40. scala-ildl.org Scopes Scopes def indexSalary(employees: Vector[Employee], by: Float): Vector[Employee] = for (employee ← employees) yield employee.copy( salary = (1 + by) * employee.salary ) Method operating on Scala collections (familiar to programmers)
41. scala-ildl.org Scopes Scopes def indexSalary(employees: Vector[Employee], by: Float): Vector[Employee] = for (employee ← employees) yield employee.copy( salary = (1 + by) * employee.salary )
42. scala-ildl.org Scopes Scopes adrt(VectorOfEmployeeSoA) { def indexSalary(employees: Vector[Employee], by: Float): Vector[Employee] = for (employee ← employees) yield employee.copy( salary = (1 + by) * employee.salary ) }
43. scala-ildl.org Scopes Scopes adrt(VectorOfEmployeeSoA) { def indexSalary(employees: Vector[Employee], by: Float): Vector[Employee] = for (employee ← employees) yield employee.copy( salary = (1 + by) * employee.salary ) } Method operating on column-based storage
44. scala-ildl.org Scopes Scopes adrt(VectorOfEmployeeJSON) { def indexSalary(employees: Vector[Employee], by: Float): Vector[Employee] = for (employee ← employees) yield employee.copy( salary = (1 + by) * employee.salary ) } Method operating on JSON data
45. scala-ildl.org Scopes Scopes adrt(VectorOfEmployeeBinary) { def indexSalary(employees: Vector[Employee], by: Float): Vector[Employee] = for (employee ← employees) yield employee.copy( salary = (1 + by) * employee.salary ) } Method operating on binary data
46. scala-ildl.org Challenges of Scopes Challenges of Scopes • Separate compilation – Storing transformation metadata • Overriding and the object model – Different signatures may not override • Passing values between scopes (composition) – Redundant conversions – Safety
47. scala-ildl.org Challenges of Scopes Challenges of Scopes • Separate compilation – Storing transformation metadata • Overriding and the object model – Different signatures may not override • Passing values between scopes (composition) – Redundant conversions – Safety • Addressed in the compiler :)
48. scala-ildl.org
49. scala-ildl.org Motivation Data-centric Optimizations Conclusion Applications
50. scala-ildl.org Array of Stuct Array of Stuct (Column-oriented) (Column-oriented) NAME ... NAME VectorOfEmployee ID ID ... ... SALARY SALARY Vector[Employee] ID NAME SALARY ID NAME SALARY 5x faster
51. scala-ildl.org Specialization Specialization 3 5 (3,5) Tuples in Scala are generic so they need to use pointers and objects
52. scala-ildl.org Specialization Specialization 3 5 3 5 (3,5) (3,5) Tuples in Scala are generic so they need to use pointers and objects + stack allocation
53. scala-ildl.org + stack allocation Specialization Specialization 14x faster reduced memory footprint 3 5 3 5 (3,5) (3,5) Tuples in Scala are generic so they need to use pointers and objects
54. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum
55. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4)
56. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8)
57. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8) 18
58. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8) 18
59. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8) 18 adrt(ListDeforestation) { List(1,2,3).map(_ + 1).map(_ * 2).sum }
60. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8) 18 adrt(ListDeforestation) { List(1,2,3).map(_ + 1).map(_ * 2).sum } accumulate function
61. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8) 18 adrt(ListDeforestation) { List(1,2,3).map(_ + 1).map(_ * 2).sum } accumulate function accumulate function
62. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8) 18 adrt(ListDeforestation) { List(1,2,3).map(_ + 1).map(_ * 2).sum } accumulate function accumulate function compute: 18
63. scala-ildl.org Deforestation Deforestation List(1,2,3).map(_ + 1).map(_ * 2).sum List(2,3,4) List(4,6,8) 18 adrt(ListDeforestation) { List(1,2,3).map(_ + 1).map(_ * 2).sum } accumulate function accumulate function compute: 18 6x faster
64. scala-ildl.org Motivation Data-centric Optimizations Conclusion Applications
65. scala-ildl.org Conclusion Conclusion • Problem: optimized representations • Solution: data-centric meta-programming – Splitting the responsibility: • Defining the Transformation programmer → • Applying the Transformation compiler → – Scopes • Adapt the data representation to the operation • Allow speculating properties of the scope
66. scala-ildl.org
67. scala-ildl.org
68. scala-ildl.org
69. scala-ildl.org Thank you!
70. scala-ildl.org Multi-Stage Programming Multi-Stage Programming • Multi-Stage Programming – “Abstraction without regret” - Tiark Rompf – DSLs small enough to be staged → • 10000x speed improvements
71. scala-ildl.org Multi-Stage Programming Multi-Stage Programming • Multi-Stage Programming – “Abstraction without regret” - Tiark Rompf – DSLs small enough to be staged → • 10000x speed improvements – Scala too large to obtain any benefit → • Separate compilation/modularization • Dynamic dispatch • Aliasing • Reflection
72. scala-ildl.org Multi-Stage Programming Multi-Stage Programming • Multi-Stage Programming – “Abstraction without regret” - Tiark Rompf – DSLs small enough to be staged → • 10000x speed improvements – Scala too large to obtain any benefit → • Separate compilation/modularization • Dynamic dispatch • Aliasing • Reflection not supported by staging. If we add support, we lose the ability to optimize
73. scala-ildl.org Low-level Optimizers Low-level Optimizers • JIT optimizers with virtual machine support – Access to the low-level code – Can assume a (local) closed world – Can speculate based on profiles – On the critical path • Limited profiles • Limited inlining • Limited analysis – Biggest opportunities are high-level - O(n2) O(n) → • Incoming code is low-level • Rarely possible to recover them
74. scala-ildl.org Low-level Optimizers Low-level Optimizers • JIT optimizers with virtual machine support – Access to the low-level code – Can assume a (local) closed world – Can speculate based on profiles – On the critical path • Limited profiles • Limited inlining • Limited analysis – Biggest opportunities are high-level - O(n2) O(n) → • Incoming code is low-level • Rarely possible to recover them Typical solution: Metaprogramming
75. scala-ildl.org Metaprogramming Metaprogramming • Not your grandpa's C preprocessor
76. scala-ildl.org Metaprogramming Metaprogramming • Not your grandpa's C preprocessor def optimize(tree: Tree): Tree = { ... }
77. scala-ildl.org Metaprogramming Metaprogramming • Not your grandpa's C preprocessor • Full-fledged program transformers – :) Lots of power def optimize(tree: Tree): Tree = { ... }
78. scala-ildl.org Metaprogramming Metaprogramming • Not your grandpa's C preprocessor • Full-fledged program transformers – :) Lots of power – :( Lots of responsibility def optimize(tree: Tree): Tree = { ... }
79. scala-ildl.org Metaprogramming Metaprogramming • Not your grandpa's C preprocessor • Full-fledged program transformers – :) Lots of power – :( Lots of responsibility • Compiler invariants • Object-oriented model • Modularity def optimize(tree: Tree): Tree = { ... }
80. scala-ildl.org Metaprogramming Metaprogramming • Not your grandpa's C preprocessor • Full-fledged program transformers – :) Lots of power – :( Lots of responsibility • Compiler invariants • Object-oriented model • Modularity def optimize(tree: Tree): Tree = { ... } Can we make metaprogramming “high-level”?