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May 30, 2023 192 likes •344 views

On Debugging Real-Time Applications F rank Mueller and David Whalley FSU Depa rtment of Computer Science DEPARTMENT OF COMPUTER SCIENCE Flo rida State Universit y T allahassee, FL 32304-4019 e-mail: mueller@cs.fsu.edu

SLIDE 1

FSU

DEPARTMENT OF COMPUTER SCIENCE

On Debugging Real-Time Applications F rank Mueller and David Whalley Depa rtment

Computer Science Flo rida State Universit y T allahassee, FL 32304-4019 e-mail: mueller@cs.fsu.edu whalley@cs.fsu.edu On Debugging Real-Time Applications LCTS'94 1

SLIDE 2

FSU

DEPARTMENT OF COMPUTER SCIENCE

Overview

debugging

pa rt

development cycle (up to 50%

time)

debuggers address real-time issues:

deadline

monito ring

time

disto rtion due to interference

debugging

debugging environment:

cache

simulation to k eep track

elapsed cycles

displa

ys elapsed execution time (cycles)

without changing debugger

ws do wn execution b y facto r

1-4

much

faster than ha rdw a re simulato rs

nd missed deadlines

lo cate time-consuming co de p

rtions

On Debugging Real-Time Applications LCTS'94 2

SLIDE 3

FSU

DEPARTMENT OF COMPUTER SCIENCE

Problems with Real-Time Debugging

time

disto rtion:

interference:

b reakp

ints,

debugger k ernel traps, caching

replace

real time with virtual time

external

events simulated

deadline

monito ring and task tuning

uni-

vs. multi-p ro cesso r On Debugging Real-Time Applications LCTS'94 3

SLIDE 4

FSU

DEPARTMENT OF COMPUTER SCIENCE

Overview

Debugging Environment

source files cache static cache configuration program

bject

files linker compiler time estimation routines control flow debugger source- level executable simulator information instruction annotation

On Debugging Real-Time Applications LCTS'94 4

SLIDE 5

FSU

DEPARTMENT OF COMPUTER SCIENCE

Real-Time Debugging Environment

elapsed

time tracing:

query

during debugging (any b reakp

int)
calculate

based

cache hit and misses simulated so fa r

translate numb er

cycles into seconds

debugging
ptimized

co de:

allo

ws realistic timing simulation

restricts

debugging to basic blo cks (b reakp

ints)
can

also displa y most va riables in registers

sometimes

inconsistent values (due to

ptimizations)

On Debugging Real-Time Applications LCTS'94 5

SLIDE 6

FSU

DEPARTMENT OF COMPUTER SCIENCE

Sample Session with dbx (dbx) stop at 43 (dbx) stop at 123 if elapsed_cycles() > 4000000 (dbx) display elapsed_cycles() [...] stopped in four at line 43 43 mmax=2; elapsed_cycles() = 29413 (dbx) next stopped in four at line 44 44 while(n>mmax) { elapsed_cycles() = 29428 [...] 123 four(tdata,nn,isign); elapsed_cycles() = 4015629 [...] elapsed cycles() = 4095351 execution completed, exit code is 1 On Debugging Real-Time Applications LCTS'94 6

SLIDE 7 F rank Mueller and David Whalley LCTS'94

reak after 4 million cycles

displa

y elapsed time

reakp

ints

do not aect virtual time k eeping

deadline

missed after 4+ million cycles (p

ints

to a rea where it's misses)

rogram terminated even later

could

set b reakp

at inner nesting level next to lo calize missed deadline On Debugging Real-Time Applications (notes) 6-1

SLIDE 8

FSU

DEPARTMENT OF COMPUTER SCIENCE

P erfo rmance Overhead unopt.

co de with time estimates co de 1kB 2kB 4kB 8kB 1.8 7.8 4.5 3.0 2.1 On Debugging Real-Time Applications LCTS'94 7

SLIDE 9 F rank Mueller and David Whalley LCTS'94

implemented
n

SP ARC

died VPO

used

db x under SunOS 4.1.3

veried

co rrectness

instruction cache simulation b y compa ring with trace-driven simulation

test p rograms

unopt.

1.8 times slo w er than

co de

instr.
pt.

2.1 to 7.8 times slo w er than

co de

instr.
pt.

1 to 4 times slo w er than common unopt. co de

cache

size inuences

verhead

(due to conicts) On Debugging Real-Time Applications (notes) 7-1

SLIDE 10

FSU

DEPARTMENT OF COMPUTER SCIENCE

F uture W

rk
external

event table

pragma

zero t imetoinser tnon

intr

usiv edebug g ing codeextendtodata caching ; pipel ining

b e used with Pthreads real-time k ernel

SP ARC VME b

roling with timing info rmation On Debugging Real-Time Applications LCTS'94 8

SLIDE 11

FSU

DEPARTMENT OF COMPUTER SCIENCE

Related W

rk
debugging

capabilities t ypically very restricted

Remedy:

interface, susp end all p ro cesso rs

b reakp

int
DCT:

sp ecial ha rdw a re (bus monito ring), non-intrusive

RED,

ART: soft w a re instrumentation, remote debugging

ARTS: (1) p rogram trace (2) debug time-stamp ed trace

rdw a re simulato rs: very slo w On Debugging Real-Time Applications LCTS'94 9

SLIDE 12 F rank Mueller and David Whalley LCTS'94

debugging

remote, indirect (o-line), not within p rogram

Remedy:
DCT:

Distributed computing testb ed

RED:

Remotely executed debugger

ART:

instrumentation p ermanent pa rt

p rograms

ARTS: Debug assistant fo r RTSs, no data queries On Debugging Real-Time Applications (notes) 9-1

SLIDE 13

FSU

DEPARTMENT OF COMPUTER SCIENCE

Summa ry

develop

ed new debugging enhancement fo r real-time

replace

real time with virtual time

eep track

virtual time b y instruction cache simulation

feasible

through static cache simulation

debug

unoptimized

r
ptimized

co de

displa

y time rep eatedly at b reakp

ints
nd

missed deadlines through conditional b reakp

ints
lo

cate time-consuming co de, tune it

tuning

ma y b e used to mak e schedule feasible

erfo rmance

verhead
f

facto r 1 to 4

unoptimized co de On Debugging Real-Time Applications LCTS'94 10