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Enhancing Live Migration Process for CPU and/or memory intensive VMs running Enterprise application - KVM forum 2011

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  • 1. Enhancing Live Migration Process for CPU and/or memory intensive VMs running Enterprise applications Benoit Hudzia CEC Belfast / SAP Research 08/2011 With the contribution of Aidan Shribman and Petter Svard
  • 2. Agenda Background: Enterprise Applications and Live Migration Warm Up Delta Compression © 2011 SAP AG. All rights reserved. 2 Delta Compression Page Priority Future Works
  • 3. Background Migrating Enterprise Class applications
  • 4. Enterprise application and Live Migration Issues •Enterprise class application: • Bigger than average resource requirement • Average SAP ERP 16GB + per VM with 32 GB of swap more than common • OLTP system such as ERP are very sensitive to time variation. • Rely heavily on precise scheduling capabilities, triggers, timers and on the ACID compliance of the underlying •Challenge when migrating such application: © 2011 SAP AG. All rights reserved. 4 •Challenge when migrating such application: • Disconnection of services: • Gigabit Ethernet timeout ≈ 5 seconds (>500 MB memory left in stop and copy phase ) • Downtime is workload dependent • Disruption of services: • Migration progressively increasing the amount of resource dedicated to itself => gradually degrade performance of the coexisting systems / VMs. • Difficulty to maintain consistency and transparency • Unpredictability and rigidity
  • 5. Warm Up for Live Migration Increasing the flexibility of Live Migration
  • 6. Warm Up Increasing flexibility Extended adaptive Pre-copy phase without triggering actual migration Increased flexibility : “just in time“ triggering of live migration Reduce down time Dynamic adaptive bandwidth allocation Manual and automatic Allow “hot standby” Facilitate WAN link transfer Classic Live Migration Threshold New Live Migration Threshold © 2011 SAP AG. All rights reserved. 6 Time Utilization Time Utilization Time Utilization Trigger Warmup Cancel Warmup Switch to full live migration
  • 7. Experimental Results: Warm-up Summary SAP Sales and Distribution Benchmark Normal Service Perceived Downtime VM Stopped Memory Transfer before stopping Normal Service WithWith WarmupWarmup WithoutWithout WarmupWarmup © 2011 SAP AG. All rights reserved. 7 WarmupWarmup VM size : 4GBVM size : 4GB SMP : 2SMP : 2 vCPUvCPU Users :Users : 150150 Load ~= 80%Load ~= 80% CPU Avg Response Time Baseline 60% 2.18 sec Warm-up 73% 2.16 sec Downtime under load: <1 sec Success ratio : ~99%
  • 8. Delta Compression of Page Limiting the impact of resending Page
  • 9. Dirty Page Delta Compression • Cache page with highest dirtying rate during send operation • Compression Algorithm: –XBRLE : XOR +binary run length encoding © 2011 SAP AG. All rights reserved. 9 encoding Vanilla (no compr.) Delta compression
  • 10. Evaluation Benchmark •Memory write benchmark (lm_bench) • 1 GB RAM, 1 vcpu VM • Near ideal case • Downtime reduced by a factor of 100 • Throughput increased by 63 % •Transcoded HD Video (VLC) • 1 GB RAM, 1 vcpu VM • Real-world, non-ideal case • UDP downtime reduced from 8 s to 1 • Migration is transparent using XBRLE • 31% faster, 51% less data sent © 2011 SAP AG. All rights reserved. 10 • Throughput increased by 63 % • 31% faster, 51% less data sent
  • 11. Evaluation- SAP ERP Sales and Distribution benchmark, load 100% • Non-responsive on resume with vanilla algorithm • Survived using XBRLE • >0.5s of downtime = risk of damaging the system • Measured downtime was 0.2s for XBRLE and 2s for vanilla • Live Migration Cpu usage directly impact ( limit ) the available resource for the ERP © 2011 SAP AG. All rights reserved. 11 damaging the system Vanilla XBRLE HW:4x 3,0GHz Xeon dual-core 32GB RAM 16TB Raid 5, 6Gbits/s trunked NFS server 1000Mbit/s Network VM:8 GB RAM, 4 vcpus VM App: SAP ERP 7.0 / S&D Benchmark
  • 12. Page Prioritization Dynamic page transfer reordering
  • 13. Dynamic page transfer reordering Prioritizing page sends ( similar to writable working set concept in Xen) © 2011 SAP AG. All rights reserved. 13
  • 14. Dynamic page transfer reordering Prioritizing page sends © 2011 SAP AG. All rights reserved. 14
  • 15. Evaluation Prio vs XBRLE : reveal Cache miss and compression efficiency Issue © 2011 SAP AG. All rights reserved. 15
  • 16. Optimizing Compression Making XBRLE more efficient
  • 17. XBZRLE Increase compression speed /efficiency •Only compress unmodified data using word aligned encoding and only encodes runs of zeros •For encoding page diffs XBZRLE is: • Compression : • 20% more efficient than XBRLE © 2011 SAP AG. All rights reserved. 17 • 20% more efficient than XBRLE • 20% less efficient than LZO/Snappy. • Speed: • Overall 2.5x-5x faster than XOR + LZO/Snappy • 11x-9x faster than the original XBRLE •Doesn’t solve the impact of cache miss
  • 18. Performance comparison Synthetic benchmark representing enterprise workload 0 500 1000 1500 2000 2500 100 600 1100 1600 2100 2600 3100 3600 Higher bandwidth (1778-2286 MB/s) © 2011 SAP AG. All rights reserved. 18 0 0.5 1 1.5 2 0 0.1 0.2 0.3 0.4 0.5 SPARSE MEDIUM DENSE V-DENSE Encoding Decoding Lower CPU time
  • 19. Performance comparison Live Migration Benchmark •Compute capacity used for live migration : • xbzrle : 50% • vanilla: between 30%-60% •Live Migration: 10 20 30 40 50 60 %usr %sys %soft Vanilla © 2011 SAP AG. All rights reserved. 19 •Live Migration: • xbzrle : terminate in seconds • Vanilla :not able to complete in the allocated time 0 0 5 10 15 20 25 30 0 10 20 30 40 50 60 0 2 4 6 8 10 12 14 %usr %sys %soft s s XBZRLE
  • 20. Future Work
  • 21. Future Works •Dynamically disable XBZRLE algorithm if the cache miss ratio is to important •Combine Page priority algorithm and XBZRLE: • Cache page with highest dirtying rate © 2011 SAP AG. All rights reserved. 21 • Eliminate unnecessary cache check • Eliminate page compression with low potential return
  • 22. Thank You! Contact information: Dr. Benoit Hudzia Senior Researcher benoit.hudzia@sap.com
  • 23. Experimentations Results: S&D Benchmark with/out warm-up ResponseResponse Time (baseline)Time (baseline) ResponseResponse Time (warmTime (warm--up)up) Time(ms) Time(ms) © 2011 SAP AG. All rights reserved. 23 Time(ms) Time(ms) 2 s response time threshold VM size : 4GBVM size : 4GB SMP : 2SMP : 2 vCPUvCPU Users : 150Users : 150 CPU Avg Response Time Baseline 60% 2.18 sec Warm-up 73% 2.16 sec 2 s response time threshold Downtime under load: <1 sec Success ratio : ~99%
  • 24. Phase 2 : Pre - copy Duration : ~ 9 min 30 sec Not successful (human timeout) Probability of Survivability of the SAP system : ~0% Phase 3 : Frozen Transfer Duration : ~2.16 sec Scenario 1 : “Classic Live Migration”Scenario 2 : “Warm-up + Live Migration” Phase 1 : Warm – up Duration : as long as we want Live Migration over emulated WAN Link Physical Server No Load 1 Vm :SAP ERP DB + CI 4GB RAM, 2 vCPU No Load Vm still alive and usable Vm Frozen Vm Alive ERP Alive © 2011 SAP AG. All rights reserved. 24 Emulated WAN Link: 10 Mb/s 350 ms latency 50 ms Jitter [1%,5%] packets drop Shared Storage
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