stack value file : custom microarchitecture for the stack

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Stack Value FileStack Value File : : Custom Microarchitecture for the StackCustom Microarchitecture for the Stack

Hsien-Hsin LeeHsien-Hsin Lee Mikhail Mikhail SmelyanskiySmelyanskiy

Chris NewburnChris Newburn Gary TysonGary Tyson

University of MichiganUniversity of Michigan

Intel CorporationIntel Corporation

2Hsien-Hsin Lee HPCA-7

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AgendaAgenda

Organization of Memory RegionsStack Reference CharacteristicsStack Value FilePerformance AnalysisConclusions


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Memory Space Memory Space PartitioningPartitioning

Based on programming language

Non-overlapped subdivisions

Split code and data I-cache & D-cache

Split data into regions– Stack ()– Heap ()– Global (static)– Read-only (static)

Protected

reserved

reservedmax mem

min mem

Read-only data

Code Region

Global Static Data Region

Heap grows upward

Stack grows downward


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Memory Access Memory Access DistributionDistribution

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Read-only

Heap ref

Static ref

Stack ref

SPEC2000int benchmark (Alpha binary) 42% instructions access memory


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Access Method Access Method BreakdownBreakdown

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Read-only ref

Heap ref

Static thru $gpr

Static thru $gp

Stack thru $gpr

Stack thru $fp

Stack thru $sp

86% of the stack references use ($sp+disp)


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Morphing $sp-relative Morphing $sp-relative ReferencesReferences

Morph $sp-relative references into register accesses

Use a Stack Value File (SVF)Resolve address early in decode stage

for stack-pointer indexed accessesResolve stack memory dependency

earlyAliased references are re-routed to

SVF


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Stack Reference Stack Reference CharacteristicsCharacteristics

Contiguity –Good temporal and spatial locality– Can be stored in a simple, fast

structure•Smaller die area relative to a regular cache

•Less power dissipation

–No address tag need for each datum


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Stack Reference Stack Reference CharacteristicsCharacteristics

First touch is almost always a StoreStore–Avoid waste bandwidth to bring in

dead data–A register write to the SVF

Deallocated stack frame–Dead data–No need to write them back to memory


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Baseline Baseline MicroarchitectureMicroarchitecture

Ld/StUnit

Instr-Cache Decoder

ArchRF

ReOrder Buffer

Fetch Decode Dispatch

Issue Execute Commit

MO

B

Reservation Station / L

SQDecoderQ

RegRenamer

(RAT) Func Unit


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Microarchitecture Microarchitecture ExtensionExtension

Hash

MaxSP

Ld/StUnit

SP

Pre-Decode

Instr-Cache

offset

Decoder

ArchRF

Value Stack

File

ReOrder Buffer



interlock

MO

B


SQDecoderQ

Reg

Morphing

Renamer(RAT) Func Unit


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Hash

MaxSP

Ld/StUnit

SP

Pre-Decode

Instr-Cache

offset

Decoder

ArchRF

Value Stack

File

ReOrder Buffer



interlock

MO

B


SQDecoderQ

Reg

Morphing


stq $r10, 24($sp)stq $r10, 24($sp)

TOSTOS


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Hash

MaxSP

Ld/StUnit

SP

Pre-Decode

Instr-Cache

offset

Decoder

ArchRF

Value Stack

File

ReOrder Buffer



interlock

MO

B


SQDecoderQ

Reg

Morphing


stq $r10, 24($sp)stq $r10, 24($sp)

33

TOSTOS


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Hash

MaxSP

Ld/StUnit

SP

Pre-Decode

Instr-Cache

offset

Decoder

ArchRF

Value Stack

File

ReOrder Buffer



interlock

MO

B


SQDecoderQ

Reg

MorphingMorphing

Renamer(RATRAT) Func Unit

stq $r10, 24($sp)stq $r10, 24($sp)

TOSTOS

$r35 $r35 ROB-18ROB-18


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Hash

MaxSP

Ld/StUnit

SP

Pre-Decode

Instr-Cache

offset

Decoder

ArchRF

Value Stack

File

ReOrder Buffer



interlock

MO

B


SQDecoderQ

Reg

MorphingMorphing


stq $r10, 24($sp)stq $r10, 24($sp)

TOSTOS

$r35 $r35 ROB-18ROB-18


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Hash

MaxSP

Ld/StUnit

SP

Pre-Decode

Instr-Cache

offset

Decoder

ArchRF

Stack

Value File

ReOrder Buffer



interlock

MO

B


SQDecoderQ

Reg

MorphingMorphing


stq $r10, 24($sp)stq $r10, 24($sp)

TOSTOS

$r35 $r35 SVF3SVF3


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Why could SVF be faster ?Why could SVF be faster ?

It reduces the latency of stack references

It effectively increases the number of memory port by rerouting more than ½ of all memory references to the SVF

It reduces contention in the MOB More flexibility in renaming stack

references It reduces memory traffic


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Simulation FrameworkSimulation FrameworkParamemters 4-wide 8-wide 16-wideDecode width 4 8 16

Issue width 4 8 16Commit width 4 8 16

IFQ size 16 32 64LSQ size 32 64 128RUU size 64 128 256DL1$ size 4w 64KB 4w 64KB 4w 64KB

DL1$ latency 3 3 3UL2$ size 4w 512KB 4w 512KB 4w 512KB

UL2$ latency 16 16 16Mem latency 60 60 60

Simple Scalar (Alpha binary), OOO model


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Speedup Potential of SVFSpeedup Potential of SVF

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

bzip2 crafty eon gap gcc gzip mcf parser twolf vortex perlbmk vpr Avg

4-wide 8-wide 16-wide 16-wide (gshare)

Assume all references can be morphed ~30% speedup for a 16-wide with dual-ported L1


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SVF Reference Type SVF Reference Type BreakdownBreakdown

86% stack references can be morphed Re-routed references enter normal memory pipeline

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

rerouted_svf_st

rerouted_svf_ld

fast_svf_st

fast_svf_ld


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Comparison with stack Comparison with stack cachecache

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6


Baseline (2+0) StackCache (2+2) SVF (2+2) Baseline (4+0)

(R+S) : RRegular and SStack or SSVF cache ports


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Memory TrafficMemory Traffic

SVF dramatically reduces memory traffic by many order of magnitude.– For gcc, ~28M (Stk$ L2) reduced to

~86K (SVF L1). Incoming traffic is eliminated because

SVF does not allocate a cache line on a miss.

Outgoing traffic consists of only those wordswords that are dirty when evicted (instead of entire cache lines).


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SVF over Baseline SVF over Baseline PerformancePerformance

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6


(1+1)/(1+0) (1+2)/(1+0) (2+2)/(2+0) (2+3)/(2+0) (2+4)/(2+0)

(R+S) : RRegular and SSVF cache ports


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ConclusionsConclusions

Stack references have several unique characteristics – Contiguity, $sp+disp, first reference

store, frame deallocation.Stack Value File

– a microarchitecture extension to exploit these characteristics

– improves performance by 24 - 65%

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Questions & AnswersQuestions & Answers

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That's all, folks !!!That's all, folks !!!

http://www.eecs.umich.edu/~linear

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Backup FoilsBackup Foils


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Stack Depth VariationStack Depth Variation


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Offset Locality of StackOffset Locality of Stack

Cumulative offset within a function call

Avg: 3b - 380b >80% offset

within“400b” >99% offset

within“8Kb”10

20

30

40

50

60

70

80

90

100

10 100 1000 10000

Offset in Bytes (Log scale)

Cu

mu

lati

ve %


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ConclusionsConclusionsStack reference features

– Contiguity– No dirty writeback when stack deallocated

Stack Value File– Fast indexing.– Alleviate multi-porting L1 cache.– Smaller, No tags, and less power.– Exploiting ILP

stack value file : custom microarchitecture for the stack

Documents

hsienhsin leehpca

stack references

custom microarchitecture

cacheoffsetdecoderar

memory space partitioningbased

sprelative referencesmorph

area relative

sp disp