lcr'02kristian kvilekval ucsb 1 prefetching for mobile computers using shape graphs kristian...

LCR'02 Kristian Kvilekval UCSB 1

Prefetching for Mobile Computers Using Shape Graphs

Kristian Kvilekval and Ambuj SinghUniversity of California, Santa Barbara


Prefetching for Mobile Applications

Cache

•Application on Mobile Computer

•Access remote store objects

•Periodic interruption

•Object Oriented Databases

•Distributed Object system


Our Approach

Code-based prefetching Prefetch only those objects accessed by the code Extract program access patterns Provide runtime system with future accesses

Advantages Complex pointer-based structures Prefetches cold misses Good accuracy


Capturing Access Pattern Statically

Shape Analysis Represents runtime data structures at compile

time as graphs

Applications: extracts properties of programs Synchronization[Bogda99][Ruf00] Parallelization[Corbera99] Safety[Ghiya96][Nurit98][Wilhem00]


Basic Shape Analysis

Graph Abstract locations (heap cells) Edges labeled with with field names

Abstract interpretation Extend graph through field references Combine graphs when heap location is shared


Example shape

class Connector{ Part a,b; }class Part { Connector left,right,up,down; Material m Supplier s; … int volume();}

weight=0;while (part) { weight+=(part.material.density *part.volume()); part=part.right.b;}

part connector

part

right

material


Construction of Shape Graphs

x



F

x.f = s;



F

G

x.f = s;t = x.f.g;



F

G

x.f = s;x.f.g = t; x = x.n;

N

?



F

G

N

x.f = s;x.f.g = t;if (x != null) x = x.n;


Combining Shape Graphs

F

G

N

F

K

J

x = y;


Combining Shape Graphs

F

G

N

F

K

J

Unify graphs recursively


Unification of Shape Graphs

F

G

N

F

K

J

G K

F J

N

Unify graphs recursively


Shape Analysis Algorithm

methods Interpret basic blocks Create shapes for basic blocks Run until fixed-point is reached

Propagate in static callgraph


Static Call Graphs

mainm2m3

m4

m3{a.f = s;o.m4(a)}Class C { m4(F f) { … }

Static representation of calls

f

Unify(a,f)


Call Graphs

Propagate bottom up Merge polymorphic calls

Recursive Calls Fixed point Merge SCC[Ruf00]

m1m2m3

m4B.m4

D1.m4

D2.m4

m1

m2

m1


Prefetching with shape graphs

Compile Time Generate shapes for method references

Self, arguments, and global variablesLabel shape edges with earliest access

Annotate programs to pass visible references and method ID to runtime

Runtime Interpret shape graph on the actual object graph


Prefetching with Shape Graphs

a1

a2

a5

a4

a3

G:5 K:10

F:10 J:10

N:5

o1:0 o4:5N

o6:10N

o2:10 o5:15

o3:20

F

K

JJ

(o1,a1) » (o4,a1) » (o2,a2) » (o6,a1) » (o5,a4) » (o3,a5)


Evaluation

Java specjvm benchmarks Track all objects accesses

Disconnects Poisson/Gaussian Duration: 500

Prefetching Interval: 2 Lookahead: 512 Cache: 2048

Cache

jess Expert System

db Address DB

mtrt ray tracer

OO7 OO database


mtrt cold-misses


OO7 all cold-misses


OO7 Startup cold-misses


Benchmarks

Benchmark Initialized INF:cold PRE:cold Time INF Time PRE

jess 11196 1182 27 328K 310K

Db 528 51 1 11002 3982

mtrt 179527 2498 3 1803K 1222K

OO7 228535 107550 1 3133K 2547K

Infinite lookahead with infinite cache


Effect of Varying Disconnect Cost


Effect of Varying Cache Size


Prefetcher Overhead

Jess \ Lookahead 0 64 256 512 1024 2048

Runtime 401K 375K 358K 357K 346K 346K

Discards 0 10K 6K 7K 7K 8.4K

wait 0 79 82 83 83 83

benchmark jess mtrt

objects 26462 209630

cache 1024 2048 4096 10240 20480 40960

Discards cache 34386 10941 6707 24132 21073 30748

Discards pre 73350 5335 1243 48432 16496 13213


Future Extensions

Accuracy and Overhead Dynamic runtime values (hashtable) Find high-payoff points (callgraph,history)

Balancing prefetching with cache, bandwidth, and power.

Tuning prefetcher to link stability And phase behavior of programs

Extend shape analysis to work at runtime Apply to non-mobile systems.


Similar Approaches

Classfiles [Krintz98] Earliest method invocation through callgraph and block analysis

Slices for multithreaded processors [Collins01][Zilles01] Preexecute data operations ahead of program

I/O extraction[Mitra00] Extract I/O related variables and execute in separate thread.


Conclusions

Code-based prefetching technique for complex pointer-based structures

Able to prefetch cold misses Good accuracy

[email protected]


New Style Applications

Mobile

Collaborative

Serverless

Dynamic

Disconnections

Sharing

Distribution

Network-topology


Calendar, Whiteboard, Bibliographer Cooperative Web cache Emergency services Games Construction/Filming/Concerts

Collaborative Mobile Applications


Prefetching for availability

File Systems Explicit or Structured

Coda [Kistler92], Ficus/Rumor/Roam [Guy98] Prediction (SEER[Keunning97])

Cluster based on file opens

Databases Attributes [Phatak99] Checkout [Holliday00] Object Bases[Knafla99]

Access patterns applied to object structure


Mobile Model

Groups

Portable

Wireless

lcr'02kristian kvilekval ucsb 1 prefetching for mobile computers using shape graphs kristian...

Documents