Execution architecture concepts - Gaudí System Architecting ...

Execution architecture concepts by Gerrit Muller Buskerud University College e-mail: [email protected] www.gaudisite.nl

Abstract The execution architecture determines largely the realtime and performance behavior of a system. Hard real time is characterized as ”missing a deadline” will result in system failure, while soft real time will result ”only” in dissatisfaction. An incremental design approach is described. Concepts such as latency, response time and throughput are illustrated. Design considerations and recommendations are given such as separation of concerns, understandability and granularity. The use of budgets for design and feedback is discussed.

hard real time systems should be explainable with a few A4 diagrams

Distribution This article or presentation is written as part of the Gaudí project. The Gaudí project philosophy is to improve by obtaining frequent feedback. Frequent feedback is pursued by an open creation process. This document is published as intermediate or nearly mature version to get feedback. Further distribution is allowed as long as the document remains complete and unchanged.

to combine or not to combine?

reasoning must be possible

limited use of tasks, threads, priorities

October 20, 2017 status: preliminary draft version: 1.1

overview is based on understanding many (critical) details

complex reality; many details, many relations

simulation: additional means if declared indispensable this is often a symptom of poor models

simulation

simple is better

Execution Architecture other architecture views

dead lines timing, throughput requirements ut

receive

execution architecture

inp

functional model demux display

Map

process

thread

store

p in

hardware CPU

DSP

RAM

ut

p in

interrupt handlers

ut

repository structure Applications play

tuner

txt

drive UI toolkit menu

foundation classes

Execution architecture concepts 2 Gerrit Muller

zap

process process process task task task thread thread thread thread thread thread

processing DCT

hardware abstraction

queue

tuner

list

DVD drive

execution architecture issues: concurrency scheduling synchronisation mutual exclusion priorities granularity

version: 1.1

October 20, 2017 CVexecutionArchitecture

Fuzzy customer view on real time

hard real time

soft real time

disastrous failure

dissatisfaction

human device safety safety

loss of functionality

loss of information

Execution architecture concepts 3 Gerrit Muller

limited throughput

loss of eye hand coordination

version: 1.1

October 20, 2017 EAChardVsSoft

waiting time

Smartening requirements Limited set of hard real time cases freq

Precise form of the distribution is not important. Be aware of systematic effects No exception allowed Worst case must fit

time 20 ms Well defined set of performance critical cases freq

Typical within desired time, limited exceptions allowed. Exceptions may not result in functional failure

90% 200 ms

Execution architecture concepts 4 Gerrit Muller

time 500 ms

version: 1.1

October 20, 2017 EACsmarteningRequirements

Latency long distance connection telephone

telephone

bla bla bla reaction

perceived delay connection latency speak listen

connection latency

bla bla bla

speak listen

reaction reaction bla bla bla time

Execution architecture concepts 5 Gerrit Muller

version: 1.1

October 20, 2017 EAClatency

Response Time

new channel

zap

total response time

P+

zap repetition

Premote control

zap

visual feedback

open for next new respons channel time

visual feedback time Execution architecture concepts 6 Gerrit Muller

version: 1.1

October 20, 2017 EACresponseTime

Throughput

speakers

tuner pip

tuner processing

screen TV

throughput: + processing steps/frame + frames/second + concurrent streams Execution architecture concepts 7 Gerrit Muller

version: 1.1

October 20, 2017 EACthroughput

Gross versus Nett bus bandwidth, processor load [memory usage] useful macroscopic views, be aware of microscopic behavior margin loss = not schedulable overhead

gross

bus, OS, scheduling

depends on design depends strongly on granularity

nett

function 4 function 3

application overhead is still in this "nett" number

function 2 function 1

Execution architecture concepts 8 Gerrit Muller

version: 1.1

October 20, 2017 EACbrutoVsNetto

Design recommendations separation of concerns

soft Real Time

process as unit of execution clear single demarcation between hard and soft

decoupling

minimize influence

queues or buffers

performance HW

HW

HW hard Real Time

minimal shared resources

Execution architecture concepts 9 Gerrit Muller

separation

manage tension explicit cost

version: 1.1

October 20, 2017 EACseparation

Design recommendations understandability hard real time systems should be explainable with a few A4 diagrams

to combine or not to combine?

reasoning must be possible

limited use of tasks, threads, priorities overview is based on understanding many (critical) details

complex reality; many details, many relations

simulation: additional means if declared indispensable this is often a symptom of poor models

simulation

simple is better Execution architecture concepts 10 Gerrit Muller

version: 1.1

October 20, 2017 EACunderstandability

Granularity considerations == == unit of or or synchronization

unit of buffering

unit of processing

video frame

video line pixel

fine grain: flexible high overhead

Execution architecture concepts 11 Gerrit Muller

coarse grain: rigid low overhead

version: 1.1

October 20, 2017 EACgranularity

== or

unit of I/O

Design patterns

synchronous

thread based

safety critical, reliable, subsystems

Asynchronous applications and services

very low overhead predictable understandable

separation of timing concerns sharing of resources (no wait)

works best in total separation does not work for multiple rhythms

poor understanding of concurrency danger of high overhead

timer based

interrupt based I/O and HW events

regular rhythm;

c n yfrm ,sp e tvilb a d

ly d ,p u sa W itrH n o m .g e

separation of timing concerns low "tunable" overhead understandable

definition of interrupts determines: overhead, understandability

fast rhythms significant overhead

Execution architecture concepts 12 Gerrit Muller

version: 1.1

October 20, 2017 EACdesignPatterns

Synchronous design

HW

SW

HW

input for tn

input for tn+1

calculate tn

calculate tn-1

execute tn-2

execute tn-1

setting tn+1 clk

input for tn+2

calculate tn+1

execute tn

calculate tn+2

execute tn+1

double buffer: full decoupling of calculation and execution

setting tn HW

Execution architecture concepts 13 Gerrit Muller

input for tn+3

version: 1.1

October 20, 2017 EACsynchronousDesign

Execution architecture concepts 14 Gerrit Muller m

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10

10 0 pi Hz xe v l t id im eo e

application needs

pa fa cka st g e et t he ra rn ns et fer

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(ps) 10-12

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from low to high level storage/network

D

cl

4

cy

FO

Actual timing on logarithmic scale

(ms) 10-3 (s) 1

October 20, 2017 RVtimeAxis

version: 1.1

from low level to high level processing times

Typical micro benchmarks for timing aspects infrequent operations, often time-intensive

often repeated operations

database

start session finish session

perform transaction query

network, I/O

open connection close connection

transfer data

high level construction

component creation component destruction

low level construction

object creation object destruction

basic programming

memory allocation memory free

function call loop overhead basic operations (add, mul, load, store)

OS

task, thread creation

task switch interrupt response

HW

power up, power down boot

cache flush low level data transfer

Execution architecture concepts 15 Gerrit Muller

method invocation same scope other context

method invocation

version: 1.1

October 20, 2017 RVuTimingBenchmarks

time

The transfer time as function of blocksize

wo

toverhead

Execution architecture concepts 16 Gerrit Muller

se a c rst

ze i s k c o l b l a optim

version: 1.1

October 20, 2017 RVparametrizedTransferRate

rate-1

block size

Example of a memory budget memory budget in Mbytes

code obj data bulk data

total

shared code User Interface process database server print server optical storage server communication server UNIX commands compute server system monitor

11.0 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

3.0 3.2 1.2 2.0 2.0 0.2 0.5 0.5

12.0 3.0 9.0 1.0 4.0 0 6.0 0

11.0 15.3 6.5 10.5 3.3 6.3 0.5 6.8 0.8

application SW total

13.4

12.6

35.0

61.0

UNIX Solaris 2.x file cache

10.0 3.0

total

74.0

Execution architecture concepts 17 Gerrit Muller

version: 1.1

October 20, 2017 RVmemoryBudgetTable

Complicating factors and measures

complications

measures

cache

considered margin

bus allocation

explicit behavior

memory management

architecture rules

garbage collection

monitoring, logging

memory (buffer, storage) fragmentation

pool management

non preemptable OS activities

feedback to architect

"hidden" dependencies (ie [dead]locks)

flipover simulation

systematic "coincidences", avalanche triggers instable response, performance

Execution architecture concepts 18 Gerrit Muller

version: 1.1

October 20, 2017 EACcomplicationsMeasures