GraphBLAS and Emus
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1) Lucata's Emu architecture features cacheless multicore processors on DRAM with hardware that migrates threads between cores to access data, providing high memory bandwidth. 2) Benchmark results show the Emu architecture achieves near-peak memory bandwidth and flat performance for a pointer-chasing workload, unlike x86 which varies with data access patterns. 3) Implementing BFS on a dynamic graph data structure achieved higher performance and bandwidth on Emu compared to x86, demonstrating Emu's suitability for streaming workloads.
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GraphBLAS and Emus
- 1. GraphBLAS and Emus Jason Riedy (all opinions my own, no planning guarantees) GraphBLAS BoF at IEEE HPEC, 22 September 2020 Lucata/ Emu Technology
- 2. Lucata’s PGAS Architecture 1 nodelet Gossamer Core 1 Memory-Side Processor Gossamer Core 4 ... Migration Engine RapidIODisk I/O 8 nodelets per node 64 nodelets per Chick RapidIO Stationary Core • Cacheless multithreaded multicore • Memory-side “processor” at narrow-channel DRAM • Stationary core for OS • Physically distributed memory • Threads migrate in hardware on reads! GraphBLAS and Emus — 22 Sep 2020 2/8
- 3. Pointer-Chasing Benchmark Data-dependent loads, fine-grained access1 Ordered 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Intra-block shuffle: weak locality 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Full block shuffle: weak locality 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 Eric Hein, Young, Srinivas Eswar, Jiajia Li, Patrick Lavin, Vuduc, Riedy. “An Initial Characterization of the Emu Chick,” Workshop on Accelerators and Hybrid Exascale Systems (AsHES) 2018. GraphBLAS and Emus — 22 Sep 2020 3/8
- 4. Selected Results: x86 Pointer-Chasing Benchmark 1 4 16 64 256 1K 4K 16K 64K 256K 1M 4M Block size (number of 16B elements) 0 20 40 60 80 100Memorybandwidth(GBs) peak STREAM bandwidth 56 threads 1 4 16 64 256 1K 4K 16K 64K 256K 1M 4M Block size (number of 16B elements) peak STREAM bandwidth 112 threads block_shuffle intra_block_shuffle full_block_shuffle Haswell results, every pattern is different.2 2 Eric Hein, Young, Srinivas Eswar, Jiajia Li, Patrick Lavin, Riedy, Vuduc, Conte. “A Microbenchmark Characterization of the Emu Chick.” Parallel Computing, 10.1016/j.parco.2019.04.012 GraphBLAS and Emus — 22 Sep 2020 4/8
- 5. Selected Results: Emu Pointer-Chasing Benchmark 1 4 16 64 256 1K 4K 16K 64K 256K 1M 4M Block size (number of 16B elements) 0 2 4 6 8 10 12 Memorybandwidth(GBs) peak STREAM bandwidth 2048 threads 1 4 16 64 256 1K 4K 16K 64K 256K 1M 4M Block size (number of 16B elements) peak STREAM bandwidth 4096 threads block_shuffle intra_block_shuffle full_block_shuffle Mostly flat performance, high utilization.2 GraphBLAS and Emus — 22 Sep 2020 5/8
- 6. Selected Results: BFS on a Dynamic Data Structure 15 16 17 18 19 20 21 scale 0 20 40 60 80 100 MTEPS Emu single node - Cilk Emu multi-node - Cilk x86 Haswell - STINGER x86 Haswell - Cilk 0 500 1000 1500 EdgeBandwidth(MB/s) Note: Streaming data structure, not statically optimized. 3 3 Hein, Eswar, Abdurrahman Yasar, Prasanth Chatarasi, Li, Young, Conte, Ümit Çatalyürek, Vuduc, Riedy, Bora Uçar. “Programming Strategies for Irregular Algorithms on the Emu Chick.” ACM ToPC, to appear. https://arxiv.org/abs/1901.02775 GraphBLAS and Emus — 22 Sep 2020 6/8
- 7. Implications for a GraphBLAS Implementation • We can be more flexible in data organization. • Not tied to CSR / CSC / COO. • NCDIMM: No cache line issues • Stride between vertices, values can be arbitrary. • Can incorporate more semantic information. • Targeting “streaming” use. • High rate of change in a massive graph. • Linked list of blocks... (STINGER, HORNET) • But must remember graphs live in a separate memory space. • Gossamer side calls stay there. • Stationary core calls must transfer input and output. GraphBLAS and Emus — 22 Sep 2020 7/8
- 8. Experiences “Porting” Existing Apps & Bindings Capabilities nice to have: • Allocating memory to hold k entries w/o knowing the type • Converting the support to a bool GxB_Matrix (T →bool) • Eases operating on masks of different types • Execution context: SC-GC, GC-GC, SC-SC • A sized blob type that is not a UDT • Sometimes used to hold keys with no GB meaning • Selects and ops with bools still useful • Users want “iterators” • Some uses are horrible to replace without a relational join-type operation • Still coming up with more... GraphBLAS and Emus — 22 Sep 2020 8/8