Investigating the Effects of Using Different Nursery Sizing Policies on Performance

Tony Guan, Witty Srisa-an, and Neo JiaDepartment of Computer Science & Engineering

University of Nebraska-Lincoln

{xguan,witty,cjia}@cse.unl.edu

Throughput performance of SPECjAppServer2004

• JBoss application server• HotSpot VM released as part

of OpenJDK1.7– Parallel generational collector

with 8 minor and 8 major collection threads

– 256 MB heap for this example (very little paging)

– Nursery and mature spaces are set to 1:2 and periodically resized to maximize throughput

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Setting the Stage …

Setting the Stage

• Performance of the generational collector has something to do with such throughput behavior– Higher workload often results in higher GC

overhead– More GC work means less useful work done

by an application

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4

Not all generational collectors are created

equal!

Motivation

• One factor that differs among different generational collector implementations is nursery sizing policy – There are multiple ways to size the nursery

and mature space– Performance ramifications of using each

policy have not been widely investigated

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Research Goals

• Can performance be affected by using different sizing policies?– Modify a VM to support multiple sizing

policies• If so, how can it be affected?

– Perform analysis by observing various metrics including execution time, throughput, GC behavior, and minimum mutator utilization

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Agenda

• Overview of investigated sizing policies• Experimental methodology• Results of our evaluation• Introducing a hybrid policy• Conclusions

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Sizing Policy: Fixed Ratio

Nursery

Nursery(33%)

Mature(66%)

Nursery(33%)

Mature(66%)

Size enlarged by 20%

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Sizing Policy: Heap Availability

Nursery

Used Mature

Nursery

UsedMature

Nursery

UsedMature

Nursery

InitialAfter

Minor_GC1After

Minor_GC2After

Minor_GCn

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Sizing Policy: GC Ergonomics

Nursery(33%)

Mature(66%)

Nursery(48%)

Mature(52%)

Nursery(40%)

Mature(60%)

Size and ratio are adjusted to meet performance goal(s)

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Terminology: Copy-Reserve*

Nursery

Initial After aMinor GC

After a fewMinor GC

Copy-Reserve

Copy-Reserve = 100% of nursery*Sizing policy = FR

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…

Mature UsedMature

UsedMature

Experimental Setting

• Three nursery sizing policies– GC Ergonomics Policy (Default)– Fixed Ratio Policy (FR) – Heap Availability Policy (HA)

• Multithreaded benchmarks– SPECjvm2008 (17)– Multithreaded benchmarks from DaCapo

(eclipse,hsqldb,lusearch,xalan)– SPECjbb2005 & SPECjAppServer2004

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Experimental Setting

• JVM (Hotspot) settings:– Memory: Old:Young=2:1

• 2 times minimum heap for each application• 256MB for jAppServer2004 and 1GB for jbb2005

– GC : 8 threads for both minor & full GC, policy modification based on parallel collector

• Platform: Intel Xeon 8 cores, 16GB, running Linux• Methodology: 5 runs, report best, worst, and

average

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Result: jvm2008 & DaCapo

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The remaining thirteen benchmarks show little sensitivity to different policies

Analysis: jvm2008 & DaCapo

App Default HA FR

Minor Full Minor Full Minor Full

Com.sunflow 3001 344 2693 301 3034 354

Derby 2639 3 5422 3 2622 3

Crypto.aes 6308 1010 2785 1540 6300 1023

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Using different sizing policies can affect the garbage collection performance

Result: jAppServer2004

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Analysis: jAppServer2004

17

Config Default HA FR

Minor Full Minor Full Minor Full

25 Tx 2523 99 11196 70 2527 86

50 Tx 205 2599 22664 238 164 2706

Analysis: jAppServer2004

Currentheap usage

Copy-Reserve = 100% of nurserySizing policy = FR or Default

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UsedMature

Copy-Reserve

Nursery

UsedMature

Copy-Reserve

Nursery

Mature heapusage after full

collection

FullCollection Used

Mature

Copy-Reserve

Nursery

FullCollection

Mature heapusage after full

collection

Analysis: jAppServer2004

Initial After aMinor GC

Nursery

Copy-Reserve Used

Mature

Nursery

Copy-Reserve

After a fewMinor GC

Copy-Reserve = 100% of nurserySizing policy = HA

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UsedMature

Nursery

Copy-Reserve

MinorCollection

MinorCollection

MMU: jAppServer2004 at 25tx

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MMU: jAppServer2004 at 40tx

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MMU: jAppServer2004 at 50tx

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Result: jbb2005

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MMU: jbb2005 at 8whs

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MMU: jbb2005 at 23whs

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Summary

• HA does not do as well as the other two policies when the workload is light

• HA allows the server to respond to requests significantly longer under heavy workload

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A Hybrid Policy

• Use default policy for the peak performance during light workload

• Use HA as soon as the GC behavior has reached a critical point– number of consecutive FullGC >=

consecFailure (e.g., 2)

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Preliminary Evaluation: jbb2005

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Preliminary Evaluation: jAppServer2004

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Preliminary Evaluation: Switching Between

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Conclusions

• Three nursery sizing policies are investigated using 23 benchmarks– Sizing policy does matter!

• It can impact performance and serviceability of large servers

– Up to 36% performance differences have been observed in some benchmarks

• The hybrid policy can be useful in large servers to better handle heavy workload

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Investigating the Effects of Using Different Nursery Sizing Policies on Performance

For source of modified hotspot & modified jbb2005 see:

http://cse.unl.edu/~xguan

Thanks!