1. Automatic Loop Parallelization
using Software Transactional Memory
Amr Abed

2. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

3. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

4. Why Parallelization?
O
Multi-cores
O
Only multi-treaded applications

5. Why automatic?
Parallel programs
O
O
Hard to implement
Legacy code
O
O
Low knowledge

6. Why loops ?
Most of execution time of a program takes
place inside loops

7. Why STM ?
O
Lock-based
O
O
O
O
Lock-free
O
O
O
Deadlock
Priority Inversion
Convoying
Not easy to implement
CAS multiple locations
STM
O
O
Easy to implement, as in lock-based
Higher performance than lock-free

8. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

9. STM
O
O
O
Each transaction performs an atomic task
Transactions run concurrently
To access shared memory
O
O
O
Write buffer
Undo log
At end, validate reads
O
O
No conflict  Commit
Conflict  Abort and restart

10. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

11. Motivation
Orec-based STM
Ring STM
Location-based metadata
TX writing to W locations
TX-based metadata
TX writing to W locations
O(W) CAS operations
Committing R/W TX
O(R+W) overhead
All validation done in CS
No CAS operations
Committing R/W TX
Single CAS operation
Bloom filters used for
validation

12. Transaction
Start
Timestamp
Write Filter
Read Filter
Write
Buffer

13. The Ring
39
40
46
41
42
Writing
45
44
43
Complete

14. Ring Entry
Commit
Timestamp
Write Filter
Status

15. Bloom Filter
Initially
0
15
1
0
14
0
0
0
13
0
12
0
11
0
0
0
10
9
8
0
0
7
0
6
0
5
0
4
0
3
0
2

16. Bloom Filter
Inserting A
A
Hash Functions
13
0
15
1
0
14
0
1
0
0
13
0
12
10
1
0
11
7
1
0
0
1
0
10
9
8
0
0
7
0
6
0
5
0
4
1
0
3
0
2

17. Bloom Filter
Inserting B
B
Hash Functions
12
0
15
1
0
14
0
1
0
1
13
0
12
9
1
11
7
0
1
0
10
9
2
1
8
0
0
7
0
6
0
5
0
1
4
1
3
0
2

18. Bloom Filter
Searching for A
A
Hash Functions
13
0
15
1
0
14
0
1
1
13
0
12
10
1
11
7
1
0
10
9
1
1
8
0
0
7
0
6
0
5
1
4
1
3
0
2

19. Bloom Filter
Searching for C
C
Hash Functions
12
0
15
1
0
14
0
1
1
13
0
12
10
1
11
3
7
1
0
10
9
1
8
0
0
7
0
6
0
5
1
4
1
3
0
2

20. Bloom Filter
Searching for D
D
Hash Functions
12
0
15
1
0
14
0
1
1
13
0
12
10
1
11
2
7
1
0
10
9
1
8
0
0
7
0
6
0
5
1
4
1
3
0
2

21. New Transaction
39
40
41
Start
Time
43 42
46
Write
Buffer
Write Filter
Read Filter
45
44
43
Writing
Complete

22. On Write
Add address to Write set
Address
Hash Functions
12
10
1
7
Write filter
0
15
1
0
14
0
1
0
1
13
0
12
1
11
0
0
10
9
1
8
0
0
7
0
6
0
1
5
0
4
1
3
0
2

23. On Write
Add <address, value> to Write buffer
Address
Value
Address
Hash Functions
12
10
Write
Buffer
1
7
Write filter
0
15
1
0
14
0
1
0
1
13
0
12
1
11
0
0
10
9
1
8
0
0
7
0
6
0
1
5
0
4
1
3
0
2

24. On Read
Address is in Write set
Address
Hash Functions
13
10
7
1
Write filter
0
15
1
0
14
0
1
1
13
0
12
1
11
1
0
10
9
1
8
0
0
7
0
6
0
5
1
4
1
3
0
2

25. On Read
Get value from write buffer
Address
Address
Hash Functions
13
10
7
Write
Buffer
1
Value
Write filter
0
15
1
0
14
0
1
1
13
0
12
1
11
1
0
10
9
1
8
0
0
7
0
6
0
5
1
4
1
3
0
2

26. On Read
Address is not in Write Set
Address
Hash Functions
12
10
3
7
Write filter
0
15
1
0
14
0
1
1
13
0
12
1
11
1
0
10
9
1
8
0
0
7
0
6
0
5
1
4
1
3
0
2

27. On Read
Get value from memory
Address
Address
Hash Functions
12
10
Memory
3
7
Value
Write filter
0
15
1
0
14
0
1
1
13
0
12
1
11
1
0
10
9
1
8
0
0
7
0
6
0
5
1
4
1
3
0
2

28. On Read
Add address to read set
Address
Hash Functions
12
10
3
7
Read filter
0
15
1
0
14
0
1
0
1
13
0
12
1
11
1
0
10
9
1
8
0
0
7
0
6
0
1
5
1
4
1
3
0
2

29. On Read
Check for conflicts
39
40
46
41
42
Start
Time
44
43
Write
Buffer
Write Filter
Read Filter
45
44
43

30. On Commit
Add new entry, and update index
47
39
40
46
41
42
Start
Time
43
Write
Buffer
Write Filter
Read Filter
45
44
43

31. On Commit
Check for conflicting writers
47
40
46
41
42
Start
Time
43
Write
Buffer
Write Filter
Read Filter
45
44
43

32. On Commit
If no conflicts, write to memory
Address
Address
Write
Buffer
Memory

33. On Commit
Set status to complete
47
40
46
45
41
42
44
43

34. Results

35. Results

36. Results

37. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

38. Motivation

39. Transaction
Start
version
Abort?
Commit
version
Commit?
Write Signature
Read Signature
Write
Buffer

40. TCM
minSV
log
PreCommit
log
Commit
log

41. Commit Log Entry
Commit
version
Transaction
pointer
Write Signature

42. Pre-commit Log Entry
Commit
Version
Transaction
Pointer
Ready?
Write Signature
Read Signature

43. New Transaction
Global Clock
Start
version
Abort?
Commit
version
Commit?
Write Signature
Read Signature
Write
Buffer

44. New Transaction
Start
version
Abort?
Commit
version
Commit?
Write Signature
Read Signature
minSV
log
Write
Buffer
PreCommit
log
Commit
log

45. Memory Access (R/W)
Same as RingSTM
Except, no eager validation on read

46. Pre-Commit
Global
Clock
Commit
Version
Transaction
Pointer
Ready?
Ready = 1
Write Filter
Read Filter

47. Pre-Commit
Commit
Version
Transaction
Pointer
Ready = 1
Write Signature
Read Signature
Commit
log

48. Commit
Address
Address
Write
Buffer
Memory

49. Results

50. Results

51. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

52. Loop parallelization
O
Non-Speculative Parallelization
DOALL
DOACROSS
DSWP
O
Speculative Parallelization
TLS
Spec-PS-DSWP

53. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

55. Speculative Pipelining
Thread 1
Thread 2
Thread 3
Slow Mode
Transition
Fast Mode

57. The Value Algorithm
Slow-mode
per-access instrumentation
Consistency Check
Fast-mode
un-instrumented speed
No false conflicts
Data forwarding

58. The Signature Algorithm
Array of write signatures
Update entry on each write
Maintain read signature
On Transition, intersect sets
Even before!

59. Results
Speedup using Value algorithm

60. Results
Speedup using Signature algorithm

61. Outline
O
O
O
O
O
O
O
Motivation
Software Transactional Memory
RingSTM
STMlite
Speculative Parallelization
Fastpath
SMTX (Spec-PS-DSWP)

62. Example code
A: while(node) {
B: node = node−>next;
C: res = work(node);
D: write(res); }
A
B
C
Control Dependency
Data Dependency
D

63. Speculation
while(TRUE) {
B: node = node−>next;
C: res = work(node);
D: write(res); }
A
B
C
Control Dependency
Data Dependency
D
B

64. Parallel Stage
Pipelining
Stage 1 (Sequential)
node = node−>next;
B
Stage 2 (Parallel)
Stage 3
(Sequential)
C
res = work(node);
C
write(res);
D

65. Execution
Core 0
0
1
2
3
4
5
Core1
Core 2
Core 3
Core 4
Core 5
B0
B1
C0
B2
C1
B3
D0
C2
D1
B4
B5
C3
C4
Try
0
D2
try1
Commit 0

66. initialization
Copy
on
Write
Main/Commit
Copy
on
Write
Virtual Address Space
Page table

67. MTX creation
Page table
Page table
Page table
Copy
on
Write
Page table
Worker 2
Virtual Address Space
Main/Commit
Page table
Page table
Page table
Copy
on
Write
Communication Channel
Virtual Address Space
Virtual Address Space
Worker 1

68. Memory access
Main/Commit
Private
Page table
Page table
Page table
Copy
on
Write
Communication Channel
Virtual Address Space
Virtual Address Space
Copy
on
Write
Page table
Worker 2
Virtual Address Space
Commit
Page table
Page table
Page table
Private
Worker 1

69. Commit
Private
Page table
Page table
Page table
Copy
on
Write
Communication Channel
Virtual Address Space
Virtual Address Space
Main/Commit
Page table
Worker 2
Virtual Address Space
Commit
Page table
Page table
Page table
Private
Worker 1

70. or
Private
Page table
Page table
Page table
Copy
on
Write
Communication Channel
Virtual Address Space
Virtual Address Space
Main/Commit
Page table
Worker 2
Virtual Address Space
Commit
Page table
Page table
Page table
Private
Worker 1

71. Rollback
Main/Commit
Private
Page table
Page table
Page table
Copy
on
Write
Communication Channel
Virtual Address Space
Virtual Address Space
Copy
on
Write
Page table
Worker 2
Virtual Address Space
Commit
Page table
Page table
Page table
Private
Worker 1

72. Results
5
SMTX
TX
4.5
4
3.5
Speedup
3
2.5
2
1.5
1
0.5
0
1
2
3
4
5
Number of threads
6
7
8

73. Thank You