GPU Performance Analysis and Optimization - GPU Technology ...

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Case Study 6: Kepler 8-byte SMEM Access• TTI Reverse Time Migration– A seismic processing code, 3DFD• fundamental component is applying a 3D stencil to 2 wavefields to compute discretederivatives– Natural to interleave the wavefields in shared memory:• store as a float2 structure• Also a slight benefit to global memory performance, on both Fermi <strong>and</strong> Kepler• Impact on performance from enabling 8-byte mode:– More SMEM operations as order in space increases– 8 th order in space:• 2 kernels, only one uses shared memory• 1.14x full code speedup (1.18x kernel speedup)– 16 th order in space:• 3 kernels, only one uses shared memory• 1.20x full code speedup (1.29x kernel speedup)© 2012, NVIDIA86
Shared Memory Bank Conflicts• A bank conflict occurs when:– 2 or more threads in a warp access different words in thesame bank• Think: 2 or more threads access different “rows” in the same bank– N-way bank conflict: N threads in a warp conflict• Instruction gets issued N times: increases latency• Note there is no bank conflict if:– Several threads access the same word– Several threads access different bytes of the same word© 2012, NVIDIA87
Page 2:
Goals of This Talk• Give insight
Page 6 and 7:
Topics For Ninjas• Topics relevan
Page 8 and 9:
EXPOSING SUFFICIENT PARALLELISM© 2
Page 10 and 11:
Memory Parallelism• Achieved Kepl
Page 12 and 13:
Occupancy• Occupancy: number of c
Page 14 and 15:
Exposing Parallelism: Grid Configur
Page 16 and 17:
Threadblock SizingToo fewthreadsper
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Case Study 1: Threadblock Sizing•
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Tail Effect• Tail underutilizes G
Page 22 and 23:
Tail Effect: Large vs Small Threadb
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General Guidelines• Threadblock s
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Kepler Memory HierarchySM-0Register
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Blocking for L1, Read-only, L2 Cach
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Global Memory Operations• Memory
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Read-only Loads• Go through the r
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Read-only Loads• Go through the r
Page 36 and 37: Caching Load• Scenario:- Warp req
Page 42 and 43: Caching Load• Scenario:- All thre
Page 46 and 47: Memory Throughput Analysis• Two p
Page 48 and 49: Two Ways to Investigate Address Pat
Page 50 and 51: Pattern Category: Offset Access•
Page 52 and 53: Case Study 2: Offset Address Patter
Page 54 and 55: Case Study 2: Remedy• Looking at
Page 56 and 57: Pattern Category 2: Large Inter-thr
Page 58 and 59: Case Study 3: Diagnosis• Double-p
Page 60 and 61: Case Study 3: Result• Naïve impl
Page 62 and 63: Case Study 4: SoA vs AoS• Global
Page 64 and 65: Case Study 4: Cause• Array of Str
Page 66 and 67: Case Study 5: Assigning More Thread
Page 68 and 69: Case Study 5: Cause and Remedy• E
Page 70 and 71: Pattern Category 4: Irregular Addre
Page 72 and 73: Summary of Pattern Categories and t
Page 74 and 75: Having Sufficient Concurrent Access
Page 76 and 77: Optimizing Access Concurrency• Ha
Page 78 and 79: Summary: GMEM Optimization• Striv
Page 80 and 81: Shared Memory• On-chip (on each S
Page 82 and 83: Kepler 8-byte Bank Mode• Mapping
Page 84 and 85: Kepler 4-byte Bank Mode• To visua
Page 88 and 89: SMEM Access ExamplesAddresses from
Page 94 and 95: Case Study 7: Matrix Transpose• S
Page 96 and 97: Summary: Shared Memory• Shared me
Page 98 and 99: Execution• Instructions are issue
Page 100 and 101: instructionsControl Flowif ( ... ){
Page 102 and 103: instructions / timeExecution diverg
Page 104 and 105: Instruction Throughput: Analysis•
Page 106 and 107: Instruction Throughput: Summary•
Page 108 and 109: Kepler Architecture Family• Two a
Page 110 and 111: Level of Parallelism• Parallelism
Page 112 and 113: Increased Shared Memory Bandwidth
Page 114 and 115: Case Study 8: More Registers Per Th
Page 116 and 117: In Conclusion• When programming a
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