Transcript slides - University of British Columbia

A GPU Accelerated Storage System
Abdullah Gharaibeh
with: Samer Al-Kiswany
Sathish Gopalakrishnan
Matei Ripeanu
NetSysLab
The University of British Columbia
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GPUs radically change the cost landscape
$600
$1279
(Source: CUDA Guide)
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Harnessing GPU Power is Challenging
 more complex programming model
 limited memory space
 accelerator / co-processor model
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Motivating Question:
Does the 10x reduction in computation costs GPUs offer
change the way we design/implement distributed systems?
Context:
Distributed Storage Systems
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Distributed Systems Computationally Intensive Operations
Operations
Hashing
Techniques
Similarity detection
Erasure coding
Content addressability
Encryption/decryption
Security
Membership testing (Bloom-filter)
Integrity checks
Compression
Redundancy
Load balancing
Summary cache
Storage efficiency
Computationally intensive
Limit performance
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Distributed Storage System Architecture
Application Layer
FS API
Metadata
Manager
Client
Files divided
into stream of
blocks
Techniques To improve Performance/Reliability
Application
Redundancy
Access
Module
Storage
Nodes
Integrity
Checks
Similarity
Detection
Security
Enabling Operations
Compression
Encryption/
Decryption
Hashing
Encoding/
Decoding
Offloading
CPU Layer
GPU
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Contributions:
 A GPU accelerated storage system:
Design and prototype implementation that integrates
similarity detection and GPU support
 End-to-end system evaluation:
2x throughput improvement for a realistic
checkpointing workload
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Challenges
 Integration Challenges
Files divided
into stream of
blocks
 Minimizing the integration effort
 Transparency
 Separation of concerns
Similarity Detection
Hashing
 Extracting Major Performance Gains
 Hiding memory allocation overheads
 Hiding data transfer overheads
Offloading Layer
 Efficient utilization of the GPU memory units
 Use of multi-GPU systems
GPU
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Past Work: Hashing on GPUs
HashGPU1: a library that exploits
GPUs to support specialized use of
hashing in distributed storage systems
Hashing
stream of
blocks
One performance data point:
Accelerates hashing by up to 5x speedup
compared to a single core CPU
HashGPU
GPU
However, significant speedup achieved only for large blocks (>16MB)
=> not suitable for efficient similarity detection
“Exploiting Graphics Processing Units to Accelerate Distributed Storage Systems” S. Al-Kiswany, A. Gharaibeh, E. Santos9
Neto, G. Yuan, M. Ripeanu,, HPDC ‘08
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Profiling HashGPU
At least
75%
overhead
Amortizing memory allocation and overlapping data transfers
and computation may bring important benefits
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CrystalGPU
CrystalGPU: a layer of abstraction
that transparently enables common
GPU optimizations
Files divided
into stream of
blocks
One performance data point:
CrystalGPU improves the speedup of
HashGPU library by more than one order
of magnitude
HashGPU
CrystalGPU
Offloading Layer
Similarity Detection
GPU
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CrystalGPU Opportunities and Enablers
Enabler: a high-level memory manager
 Opportunity: overlap the communication
and computation
Files divided
into stream of
blocks
Similarity Detection
HashGPU
Enabler: double buffering and
asynchronous kernel launch
CrystalGPU
Memory
Manager
 Opportunity: multi-GPU systems (e.g.,
GeForce 9800 GX2 and GPU clusters)
Task Queue
Double
Buffering
GPU
Enabler: a task queue manager
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Offloading Layer
 Opportunity: Reusing GPU memory buffers
Experimental Evaluation:
 CrystalGPU evaluation
 End-to-end system evaluation
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CrystalGPU Evaluation
Testbed: A machine with
CPU: Intel quad-core 2.66 GHz with PCI Express 2.0 x16 bus
GPU: NVIDIA GeForce dual-GPU 9800GX2
Files divided
into stream of
blocks
Experiment space:
 HashGPU/CrystalGPU vs. original HashGPU
 Three optimizations
 Buffer reuse
 Overlap communication and computation
 Exploiting the two GPUs
HashGPU
CrystaGPU
GPU
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HashGPU Performance on top CrystalGPU
Base Line:
CPU Single Core
The gains enabled by the three optimizations can be realized!
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End-to-End System Evaluation
 Testbed
– Four storage nodes and one metadata server
– One client with 9800GX2 GPU
 Three implementations
– No similarity detection (without-SD)
– Similarity detection
• on CPU (4 cores @ 2.6GHz) (SD-CPU)
• on GPU (9800 GX2) (SD-GPU)
 Three workloads
– Real checkpointing workload
– Completely similar files: all possible gains in terms of data saving
– Completely different files: only overheads, no gains
 Success metrics:
– System throughput
– Impact on a competing application: compute or I/O intensive
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System Throughput (Checkpointing Workload)
1.8x improvement
The integrated system preserves the throughput gains on
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a realistic workload!
System Throughput (Synthetic Workload of Similar Files)
Room for 2x
improvement
Offloading to the GPU enables close to optimal performance!
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Impact on Competing (Compute Intensive) Application
Writing Checkpoints back to back
2x
improvement
7% reduction
Frees resources (CPU) to competing applications while
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preserving throughput gains!
Summary
 We present the design and implementation of a distributed
storage system that integrates GPU power
 We present CrystalGPU: a management layer that transparently
enable common GPU optimizations across GPGPU applications
 We empirically demonstrate that employing the GPU enable close
to optimal system performance
 We shed light on the impact of GPU offloading on competing
applications running on the same node
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netsyslab.ece.ubc.ca
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Similarity Detection
Hashing
File A
X
Y
Z
Potentially improving write
throughput
Only the first block is different
Hashing
File B
W
Y
Z
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Execution Path on GPU – Data Processing Application
1. Preprocessing
(memory allocation)
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2. Data transfer in
3. GPU Processing
4. Data transfer out
5. Postprocessing
1
2
4
5
1
2
3
4
5
TTotal = TPreprocesing + TDataHtoG + TProcessing + TDataGtoH + TPostProc
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