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Ingredients

  • 1 c Finely chopped onions
  • 2 Garlic cloves, minced or
  • Pressed 1 sm Fresh Chile, seeded and
  • Minced 1/4 ts Salt
  • 3 To 4 cups vegetable broth
  • (divided use) 2 ts Ground cumin
  • 1 md Sweet potato, diced (about 2
  • Cups) 1 sm Red bell pepper, finely
  • Chopped 3 c Fresh or frozen corn

Kernels Reduced-fat sour cream and Finely chopped Cilantro leaves for garnish (optional) In covered soup pot, simmer onions, garlic, Chile and salt in 1 cup of vegetable broth for about 10 minutes, or until onions are soft. In small bowl, make a paste with cumin and 1 tablespoonful of broth, stir it into the pot, and simmer for another 1 to 2 minutes. Add sweet potato and remaining broth and simmer for 10 minutes, until sweet potato softens. Add bell pepper and corn, and simmer, covered, for another 10 minutes, or until all of the vegetables are tender. Puree about half of the soup in blender or food pro- cessor and return it to the pot. The soup will be creamy and thick. Add another cup of vegetable broth, if desired, plus salt to taste. Gently reheat on low heat. If desired, top with a dollop of reduced-fat sour cream and chopped cilantro. Makes 4 servings. Per serving: Calories 239 Trace of fat No cholesterol Sodium 273 mg Adapted From Moosewood Restaurant Low-Fat Favorites Adapted and typos by Bobbie Beers

1 answer


Answer:

CONSTITUTION-MAKING PROCESS

Independent Nigeria has so far experimented with five constitutions, the 1960, 1963, 1979, 1989 and 1999 constitutions. (The 1989 Constitution was not promulgated). The 1999 Constitution has given birth to the Fourth Republic, though with prob- lems for which it faces demands for a revision or amendment. The first two of these constitutions were drawn up during civilian regimes while the last three were made or promulgated during military regimes.

Some of the lessons learned by Nigerians dur- ing these exercises are enduring. The lessons have been taught and learned that no constitution is perfect; that ineffective constitutions can be amend- ed or completely altered; that constitution - making, whether under a military or civilian regime, calls for adequate consultations and experimentation.

Furthermore, as was the experience with the 1963, 1979 and 1999 Constitutions, any constitution that is hurriedly drawn up and not tried, stands the risk of failure when subjected to the pressure of political, legal, economic and social forces in and outside the society.

ELIMINATION OF ANACHRONISMS

Between 1960 and 1963, certain anachronisms inherited at independence were done away with. Nigeria learned some lessons from the Western Region crisis of 1962 during which the Premier, late Chief S. L. Akintola, was removed from office by the Governor of the Region, Sir Adesoji Aderemi, through the exercise of executive powers. Also very instructive were the three important court cases that resulted there- from: Akintola v Aderemi (1963); Akintola vAdegbenro (1963); and Adegbenro vAkintola (1963). Nigeria has learned that political and constitutional conventions should be applied with restraint and, if possible, carefully guided by means of constitutional provi- sions; that no single individual, however dignified and trusted, should have the power to appoint or remove the Head of State or Head of Government; and, that a strong Republican Constitution should replace the old Monarchical Constitution inherited from Britain. These lessons served as the back- drop against which the 1963 Republican Constitution was drawn.

One other lesson learned relates to the position and authority of Nigeria's Supreme Court. The majority decision in Akintola vs Aderemi (1963) went in favour of Chief S. L. Akintola but one of the Judges of the Supreme Court, Sir Lionel Brett, dis- sented. On further appeal to the Privy Council in Britain, the decision of the Supreme Court was over-ruled. Nigeria's reaction was sharp. Nigeria's 1960 Constitution was amended to delete the requirement for a final appeal to the Privy Council in Britain.

The Republican Constitution of 1963 was contemplated and later introduced to replace the Governor-General with a President. This further severed the links between Nigeria and Britain in political and constitutional matters. Subsequently, the Nigerian Supreme Court was fully Nigerianised. The abolition of the Parliamentary system of gov- ernment in Nigeria on 1st October, 1979 completed the process of change from the old monarchical order, inherited from Britain, to a republican order.

POLITICAL AND CONSTITUTIONAL DOCTRINES

Nigeria has maintained a written Constitution as the supreme law of the country. Thus, there is a departure from the British unwritten political and constitutional principle. She has also maintained two (and as from 1979, three) separate lists staling the functions of the Federal, State and Local Governments.

In order to strengthen the hands and position of the Federal Government for purposes of legislation and control, Nigeria has adopted from America the doctrine of Repugnancy and from Australia, the doctrine of Covering the Field. By the doctrine of Repugnancy, the Nigerian Constitution maintains that any law which is inconsistent with the provi- sions of the Constitution, shall be void to the extent of the inconsistency. By the doctrine of Covering the Field, it is maintained that the Federal Government can legislate on any matter which it has legislative competence. Any State laws which are inconsistent with a Federal legislation on the same subject shall, to the extent of its inconsisten- cy, be void and inoperative. Thus, politically and constitutionally, the Federal Republic of Nigeria is a strong Federation.

POLITICAL AND CONSTITUTIONAL CONCEPTS AND CONVENTIONS

Nigeria initially followed the British practice of separation of powers, with a strong emphasis on judicial independence. From 1960 to 1966, the Prime Minister and his ministers sat in the legisla- ture and formed the Government. They helped in making and enforcing the laws. Premiers and their ministers did likewise in the Regions. The parlia- mentary system in Nigeria took the form of the "Split Executive System". By 1979, she moved towards the American practice where stricter principles of separation of powers are practiced.

The President has become an Executive one and State Governors are Executives. They no longer sit in the legislatures. The independence of the judiciary has been reinforced in several cases, including Kalu Anya v Borno State House of Assembly and Other (1984). In this case, an effort at arbitrary removal from office of Mr Justice Kalu Anya, the then Chief Judge of Borno State, was resisted and declared null and void by the Supreme Court.

The principle of Separation of Powers and the doctrine of Repugnancy were also reinforced. In Balarabe Musa v Kaduna House of Assembly (1981), the principle of Separation of Powers and judicial respect for the Legislatures and their privi- leges were sustained. In the latter case, the removal of Balarabe Musa, the then State Governor, by the Kaduna State House of Assembly, through Impeachment Procedure, as provided for in the 1979 Constitution, was endorsed by the Supreme Court.

Nigeria has also maintained the concept or principle of the Rule of Law inherited from Britain. Legislative supremacy is limited by the Constitution. Leoislation declared bv the courts to be in violation of the constitution are null and void.

HUMAN RIGHTS

Considerable progress has also been made in the area of human rights. Adequate provision for the enforcement of the fundamental human rights of Nigerian citizens is made in the Nigerian Constitution and are regularly upheld by the courts when they are breached.

The Nigerian Constitution also guarantees to Nigerian citizens the right to fair hearing and repre- sentation by counsel of choice. The Constitutional right to freedom of con- science and religion has been upheld by the courts. The Constitutional right to freedom of expression, movement and to hold opinions has also been upheld by the Courts.

CITIZENSHIP QUESTION

The rights and privileges of Nigerian citizens have been carefully provided for in the Nigerian Constitution. In Shugaba's case (1981), it was illus- trated beyond doubt that those provisions are not to be taken lightly. An attempt by the Minister of Internal Affairs to deport Shugaba Darman, purport- ing him to be a non-Nigerian, was declared null and void. Arbitrary executive action was, thus, success- fully challenged and kept in check in line with the principles of the Rule of Law and supremacy of the Constitution. In addition, scandalous abuse of the constitutional rights of citizens has been frowned upon by the courts.

CENSUS

Nigeria has learned lessons from the disputed Census of 1963 and that of 1973 which was can- • celled. The conduct of the 1991 Census was care- fully planned and executed to the admiration of the , majority of well-meaning Nigerians. The principle has been upheld that political, constitutional and socio-economic planning and development without a sound census or realistic population basis is doomed to fail.

THE MINORITY QUESTION

This has, since the 1950s, been a very con- tentious issue which led to the setting up of a full- scale Commission of Inquiry; The Willinks Commission of Inquiry from 1957 to 1958. The issue was largely responsible for most of the politi- cal and constitutional problems between 1960 and 1966. Efforts have been made to address the prob- lem since 1967 through the process of creation of states and local governments, and the observance of the principles of Federal Character and Local Govern-ment spread as political and constitutional principles.

Before the outbreak of the Nigerian Civil War in 1967, the Federal Government, under General Yakubu Gowon, abolished the existing Regions and created, in their stead, twelve States. The Murtala Mohammed regime created seven more States in 1976, thus bringing the total number of states in the Federation then to nineteen. It also created a new Federal Capital Territory in Abuja. The Babangida regime raised the total number of states to twenty- one in 1987 and then to thirty in 1991. The Abacha administration raised the number of states to thirty- six in October, 1996.

Since 1976, the Local Government System in Nigeria has undergone radical reforms. In 1976, a total of 306 Local Governments were created by the Murtala/Obasanjo regime. The Babangida regime raised the number to 449 in 1987 and to 589 in 1991, while the Abacha regime raised the number further to 774 in 1996.

ACCOUNTABILITY

The concept of accountability was identified, as far back as during the Colonial regime, as an impor- tant factor in the political and constitutional devel- opment of Nigeria. It received a boost consequent to the celebrated Foster-Sutton Commission of Inquiry in 1955. Since then, the concept has been reinforced in practice. This is exemplified by the fol- lowing: constitutional protection for Auditors- General of the Federal, States and Local Governments; and, in particular, the operation of the Ombudsman system as a political and constitu- tional principle.

Nigeria's Ombudsman system consists of the Public Complaints Commission (Federal and State) and the Code of Conduct Bureau and Tribunal. Decree No 43 of 1988 (now abrogated) on Civil Service Reforms had a schedule which dealt with accountability as a national issue with appropriate sanctions. The rules concerning accountability are now protected by several other laws and revised Civil Service Rules. In 1999, the Obasanjo Administration introduced an Anti-Corruption bill to the Legislature in furtherance of the objective.

TRANSITION TO CIVIL RULE: A RIGHT INCLINE

Between 1983 and 1998, the choice of a correct model of Transition to Civil Rule Programme eluded Nigerians, thrice. Before its final collapse, the Babangida Administration tried two models of the Transition to Civil Rule Programme. The first was the Machiavellian model, characterised by uncer- tainty, prevarications and inability to fix a consistent handing over date. The second was a modified Egyptian or Abdul Nasser model, characterised by a tendency towards self-succession by the incum- bent ruler or President. In the latter case, Babangida had, allegedly, hoped to obtain his endorsement as a civilian President for the Third Republic by an Act of the National Assembly. The bid failed. He then "stepped aside" on 27 August 1993, but shoved into office an Interim National Government headed bv Chief Ernest Shonekan.

Shonekan's government was declared illegal by a Lagos High Court and booted out of office in a palace coup d'etat master-minded by General Sani Abacha.

Thereafter, a third attempt at choosing a model of transition to civil rule was made during Abacha's tenure as Head of State. His choice was, obvious- ly, the Egyptian model with a bid for self succession, this time around, by means of an election in which he was to be declared legally a "Consensus Candidate", adopted by the five government- approved political parties. He had almost achieved his aim, but on 8 June, 1998, he died.

General Abdulsalami Abubakar was the suc- cessor to General Abacha. As soon as he was firm- ly on the saddle, he proclaimed his administration's support for a genuine democracy, an early return to civil rule and handing over of power to a democrat- ically elected civilian government on 29th May, 1999. He planned and implemented a programme that eventually brought in the Fourth Republic with Chief Olusegun Obasanjo as the President .

THE ELECTIVE EXECUTIVE PRESIDENT

As soon as Obasanjo assumed power as President, he chose to become an effective Executive President. This predisposed him to three obvious choices among the prevailing presidential power theories: the residual power; the inherent power; or, the specific great power model. He seemingly chose the inherent power model by which he hoped to return stability to Nigeria, do away with crippling redundant and conflicting laws; place the military in the barracks; retire the old guards; and maintain national boundaries within peaceful limits.

Some Nigerians have decried some of Obasanjo's actions and utterances as unpleasant and uncharitable, but certainly no one has success- fully challenged the legality and constitutionality of those actions and utterances, including his expung- ing of the old conflicting laws under the provisions of Section 315(1), (2) and (3) of the 1999 Nigerian Constitution and his threat to impose a state of emergency on Delta, Bayelsa and Lagos States where youth crises had threatened to reach a destabilising level.

THE FOURTH REPUBLIC

Nigeria's Fourth Republic came into being on 29 May, 1999. There is every sign of success on its way, nationally and internationally. A National Rebirth Programme has been launched and its suc- cess demands the committed participation of all Nigerians. It is hoped that democratic government has, indeed, come to stay in Nigeria, with this Fourth Republic.

SOME PROBLEMS

Nigeria, in spite of her progress, still faces several seemingly intractable political and constitution- al problems. The experience of constitution-making in Nigeria, though almost a generation and half old, still faces various problems. Among these are the controversies over the distribution of powers between the Legislature, the Executive and the Judiciary; Executive or Split Executive of the Presidential system; operation of the party system in its new form; the role of the Independent National Electoral Commission and the limits of its powers; and the choice of a satisfactory formula for political party formation that can guarantee stability and progress in the election of a President.

In the last case, between 1960 and 1963, Nigeria was ruled by a coalition between the domi- nant political parties in the North and the East to the exclusion of that in the West. Between 1964 and 1966, the Federal Government was largely a coali- tion between the North and the West, to the exclu- sion of the East. Furthermore, between 1979 and 1983, the formula of the North-East coalition was revived with some recognition for the eastern minorities. With respect to the Third Republic, how- ever, the formula was not clear until the collapse of that Republic. In the Fourth Republic, the formula of coalition between the West and the North has been revived but with considerable recognition for the East and the Minorities.

CONCLUSION

There are signs of further progress in line with the enthusiasm and commitment that often accompany moments of change. Reforms of the nation's political and constitutional machinery, bureaucracy, economic and social structures are still in progress in the Fourth Republic.

In her political and constitutional experience and developments, Nigeria has passed the classi- cal phase. She is now making progress, though not without considerable difficulties, through the later years of the human relations phase. Hopefully, in no distant future, she will reach the dawn of the sys- tems phase, now in vogue in the industrialised countries of the world. The transition to civil rule already completed and the Fourth Republic now firmly in place are definitely pointers in the right

FURTHER READING

Aguda, T. A., (1985) "Constitutions and Constitutional Changes", in J. A. Atanda and A.Y. Aliyu (Eds.) Proceedings of the National Conference on Nigeria Since Independence: Political Development, Zaria: Gaskiya Corporation, 1985. Nwabueze, B. 0. (1985) Nigeria's Presidential Constitution, London: Longman, 1985. "First Hundred Days in Office - Olusegun Obasanjo", Newswatch Magazine (Special Edition), September 13.1999.

Nwabueze, B. 0., Presidentialism in Commonweath Africa, London: C. Hurst and Company, Pp I I - 16.

Tempo Newspaper, Vol. 13, No. 23, P. 8. 16 December, 1999.

3 answers


MPI

(Message

P

assing

In

terface)

is

sp

eciØcation

for

message-passing

libraries

that

can

b

e

used

for

writing

p

ortable

parallel

programs.

What

do

es

MPI

do?

When

w

e

sp

eak

ab

out

parallel

programming

using

MPI,

w

e

imply

that:

A

Øxed

set

of

pro

cesses

is

created

at

program

initialization,

one

pro

cess

is

created

p

er

pro

cessor

Eac

h

pro

cess

kno

ws

its

p

ersonal

n

um

b

er

Eac

h

pro

cess

kno

ws

n

um

b

er

of

all

pro

cesses

Eac

h

pro

cess

can

comm

unicate

with

other

pro

cesses

Pro

cess

can't

create

new

pro

cesses

(in

MPI{1),

the

group

of

pro

cesses

is

static

What

is

PVM?

PVM

(P

arallel

Virtual

Mac

hine)

is

a

soft

w

are

pac

k

age

that

allo

ws

a

heterogeneous

collection

of

w

orkstations

(host

p

o

ol)

to

function

as

a

single

high

p

erformance

parallel

virtual

mac

hine.

PVM,

through

its

virtual

mac

hine,

pro

vides

a

simple

y

et

useful

distributed

op

erating

system.

It

has

daemon

running

on

all

computers

making

up

the

virtual

mac

hine.

PVM

daemon

(p

vmd)

is

UNIX

pro

cess,

whic

h

o

v

ersees

the

op

eration

of

user

pro

cesses

within

a

PVM

application

and

co

ordinates

in

ter-mac

hine

PVM

comm

unications.

Suc

h

p

vmd

serv

es

as

a

message

router

and

con

troller.

One

p

vmd

runs

on

eac

h

host

of

a

virtual

mac

hine,

the

Ørst

p

vmd,

whic

h

is

started

b

y

hand,

is

designated

the

master,

while

the

others,

started

b

y

the

master,

are

called

sla

v

es.

It

means,

that

in

con

trast

to

MPI,

where

master

and

sla

v

es

start

sim

ultaneously

,

in

PVM

master

m

ust

b

e

started

on

our

lo

cal

mac

hine

and

then

it

automatically

starts

daemons

on

all

other

mac

hines.

In

PVM

only

the

master

can

start

new

sla

v

es

and

add

them

to

conØguration

7

or

delete

sla

v

e

hosts

from

the

mac

hine.

Eac

h

daemon

main

tains

a

table

of

conØguration

and

handles

information

relativ

e

to

our

parallel

virtual

mac

hine.

Pro

cesses

comm

unicate

with

eac

h

other

through

the

daemons:

they

talk

to

their

lo

cal

daemon

via

the

library

in

terface

routines,

and

lo

cal

daemon

then

sends/receiv

es

messages

to/from

remote

host

daemons.

General

idea

of

using

MPI

and

PVM

is

the

follo

wing:

The

user

writes

his

application

as

a

collection

of

co

op

erating

pro

cesses

(tasks),

that

can

b

e

p

er-

formed

indep

enden

tly

in

diÆeren

t

pro

cessors.

Pro

cesses

access

PVM/MPI

resources

through

a

library

of

standard

in

terface

routines.

These

routines

allo

w

the

initiation

and

termination

of

pro-

cesses

across

the

net

w

ork

as

w

ell

as

comm

unication

b

et

w

een

pro

cesses.

3.3

What

is

not

diÆeren

t?

Despite

their

diÆerences,

PVM

and

MPI

certainly

ha

v

e

features

in

common.

In

this

section

w

e

review

some

of

the

similarities.

3.3.1

P

ortabilit

y

Both

PVM

and

MPI

are

p

ortable;

the

sp

eciØcation

of

eac

h

is

mac

hine

indep

enden

t,

and

im-

plemen

tations

are

a

v

ailable

for

a

wide

v

ariet

y

of

mac

hines.

P

ortabilit

y

means,

that

source

co

de

written

for

one

arc

hitecture

can

b

e

copied

to

a

second

arc

hitecture,

compiled

and

executed

without

mo

diØcation.

3.3.2

MPMD

Both

MPI

and

PVM

p

ermit

diÆeren

t

pro

cesses

of

a

parallel

program

to

execute

diÆeren

t

exe-

cutable

binary

Øles

(This

w

ould

b

e

required

in

a

heterogeneous

implemen

tation,

in

an

y

case).

That

is,

b

oth

PVM

and

MPI

supp

ort

MPMD

programs

as

w

ell

as

SPMD

programs,

although

again

some

implemen

tation

ma

y

not

do

so

(MPICH,

LAM

{

supp

ort).

3.3.3

In

terop

erabilit

y

The

next

issue

is

in

terop

erabilit

y

{

the

abilit

y

of

diÆeren

t

implemen

tations

of

the

same

sp

eciØ-

cation

to

exc

hange

messages.

F

or

b

oth

PVM

and

MPI,

v

ersions

of

the

same

implemen

tation

(Oak

Ridge

PVM,

MPICH,

or

LAM)

are

in

terop

erable.

3.3.4

Heterogeneit

y

The

next

imp

ortan

t

p

oin

t

is

supp

ort

for

heterogeneit

y

.

When

w

e

wish

to

exploit

a

collection

of

net

w

ork

ed

computers,

w

e

ma

y

ha

v

e

to

con

tend

with

sev

eral

diÆeren

t

t

yp

es

of

heterogeneit

y

[GBD

+

94]:

arc

hitecture

The

set

of

computers

a

v

ailable

can

include

a

wide

range

of

arc

hitecture

t

yp

es

suc

h

as

PC

class

mac

hines,

high-p

erformance

w

orkstations,

shared-memory

m

ultipro

cessors,

v

ector

sup

ercom-

puters,

and

ev

en

large

MPPs.

Eac

h

arc

hitecture

t

yp

e

has

its

o

wn

optimal

programming

metho

d.

Ev

en

when

the

arc

hitectures

are

only

serial

w

orkstations,

there

is

still

the

prob-

lem

of

incompatible

binary

formats

and

the

need

to

compile

a

parallel

task

on

eac

h

diÆeren

t

mac

hine.

8

data

format

Data

formats

on

diÆeren

t

computers

are

often

incompatible.

This

incompatibilit

y

is

an

imp

or-

tan

t

p

oin

t

in

distributed

computing

b

ecause

data

sen

t

from

one

computer

ma

y

b

e

unreadable

on

the

receiving

computer.

Message

passing

pac

k

ages

dev

elop

ed

for

heterogeneous

en

viron-

men

ts

m

ust

mak

e

sure

all

the

computers

understand

the

exc

hanged

data;

they

m

ust

include

enough

information

in

the

message

to

enco

de

or

deco

de

it

for

an

y

other

computer.

computational

sp

eed

Ev

en

if

the

set

of

computers

are

all

w

orkstations

with

the

same

data

format,

there

is

still

heterogeneit

y

due

to

diÆeren

t

computational

sp

eeds.

The

problem

of

computational

sp

eeds

can

b

e

v

ery

subtle.

The

programmer

m

ust

b

e

careful

that

one

w

orkstation

do

esn't

sit

idle

w

aiting

for

the

next

data

from

the

other

w

orkstation

b

efore

con

tin

uing.

mac

hine

load

Our

cluster

can

b

e

comp

osed

of

a

set

of

iden

tical

w

orkstations.

But

since

net

w

ork

ed

com-

puters

can

ha

v

e

sev

eral

other

users

on

them

running

a

v

ariet

y

of

jobs,

the

mac

hine

load

can

v

ary

dramatically

.

The

result

is

that

the

eÆectiv

e

computational

p

o

w

er

across

iden

tical

w

orkstations

can

v

ary

b

y

an

order

of

magnitude.

net

w

ork

load

Lik

e

mac

hine

load,

the

time

it

tak

es

to

send

a

message

o

v

er

the

net

w

ork

can

v

ary

dep

ending

on

the

net

w

ork

load

imp

osed

b

y

all

the

other

net

w

ork

users,

who

ma

y

not

ev

en

b

e

using

an

y

of

the

computers

in

v

olv

ed

in

our

computation.

This

sending

time

b

ecomes

imp

ortan

t

when

a

task

is

sitting

idle

w

aiting

for

a

message,

and

it

is

ev

en

more

imp

ortan

t

when

the

parallel

algorithm

is

sensitiv

e

to

message

arriv

al

time.

Th

us,

in

distributed

computing,

heterogeneit

y

can

app

ear

dynamically

in

ev

en

simple

setups.

Both

PVM

and

MPI

pro

vide

supp

ort

for

heterogeneit

y

.

As

for

MPI,

diÆeren

t

datat

yp

es

can

b

e

encapsulated

in

a

single

deriv

ed

t

yp

e,

thereb

y

allo

wing

comm

unication

of

heterogeneous

messages.

In

addition,

data

can

b

e

sen

t

from

one

arc

hitecture

to

another

with

data

con

v

ersion

in

heterogeneous

net

w

orks

(big-endian,

little-endian).

Although

MPI

sp

eciØcation

is

designed

to

encourage

heterogeneous

implemen

tation,

some

implemen

tations

of

MPI

ma

y

not

b

e

used

in

a

heterogeneous

en

vironmen

t.

Both

the

MPICH

and

LAM

are

implemen

tations

of

MPI,

whic

h

supp

ort

heterogeneous

en

vironmen

ts.

The

PVM

system

supp

orts

heterogeneit

y

in

terms

of

mac

hines,

net

w

orks,

and

applications.

With

regard

to

message

passing,

PVM

p

ermits

messages

con

taining

more

than

one

datat

yp

e

to

b

e

exc

hanged

b

et

w

een

mac

hines

ha

ving

diÆeren

t

data

represen

tations.

In

summary

,

b

oth

PVM

and

MPI

are

systems

designed

to

pro

vide

users

with

libraries

for

writing

p

ortable,

heterogeneous,

MPMD

programs.

3.4

DiÆerences

PVM

is

built

around

the

concept

of

a

virtual

mac

hine

whic

h

is

a

dynamic

collection

of

(p

oten-

tially

heterogeneous)

computational

resources

managed

as

a

single

parallel

computer.

The

virtual

mac

hine

concept

is

fundamen

tal

to

the

PVM

p

ersp

ectiv

e

and

pro

vides

the

basis

for

heterogeneit

y

,

p

ortabilit

y

,

and

encapsulation

of

function

that

constitute

PVM.

In

con

trast,

MPI

has

fo

cused

on

message-passing

and

explicitly

states

that

resource

managemen

t

and

the

concept

of

a

virtual

mac

hine

are

outside

the

scop

e

of

the

MPI

(1

and

2)

standard

[GKP96

].

9

3.4.1

Pro

cess

Con

trol

Pro

cess

con

trol

refers

to

the

abilit

y

to

start

and

stop

tasks,

to

Ønd

out

whic

h

tasks

are

running,

and

p

ossibly

where

they

are

running.

PVM

con

tains

all

of

these

capabilities

{

it

can

spa

wn/kill

tasks

dynamically

.

In

con

trast

MPI

{1

has

no

deØned

metho

d

to

start

new

task.

MPI{2

con

tains

functions

to

start

a

group

of

tasks

and

to

send

a

kill

signal

to

a

group

of

tasks

[NS02].

3.4.2

Resource

Con

trol

In

terms

of

resource

managemen

t,

PVM

is

inheren

tly

dynamic

in

nature.

Computing

resources

or

"hosts"

can

b

e

added

and

deleted

at

will,

either

from

a

system

"console"

or

ev

en

from

within

the

user's

application.

Allo

wing

applications

to

in

teract

with

and

manipulate

their

computing

en

vironmen

t

pro

vides

a

p

o

w

erful

paradigm

for

load

balancing

|

when

w

e

w

an

t

to

reduce

idle

time

for

eac

h

mac

hine

in

v

olv

ed

in

computation

task

migration

|

user

can

request

that

certain

tasks

execute

on

mac

hines

with

particular

data

formats,

arc

hitectures,

or

ev

en

on

an

explicitly

named

mac

hine

fault

tolerance

Another

asp

ect

of

virtual

mac

hine

dynamics

relates

to

e±ciency

.

User

applications

can

exhibit

p

oten

tially

c

hanging

computational

needs

o

v

er

the

course

of

their

execution.

F

or

example,

con-

sider

a

t

ypical

application

whic

h

b

egins

and

ends

with

primarily

serial

computations,

but

con

tains

sev

eral

phases

of

hea

vy

parallel

computation.

PVM

pro

vides

∞exible

con

trol

o

v

er

the

amoun

t

of

computational

p

o

w

er

b

eing

utilized.

Additional

hosts

can

b

e

added

just

for

those

p

ortions

when

w

e

need

them.

MPI

lac

ks

suc

h

dynamics

and

is,

in

fact,

sp

eciØcally

designed

to

b

e

static

in

nature

to

impro

v

e

p

erformance.

Because

all

MPI

tasks

are

alw

a

ys

presen

t,

there

is

no

need

for

an

y

time-consuming

lo

okups

for

group

mem

b

ership.

Eac

h

task

already

kno

ws

ab

out

ev

ery

other

task,

and

all

com-

m

unications

can

b

e

made

without

the

explicit

need

for

a

sp

ecial

daemon.

Because

all

p

oten

tial

comm

unication

paths

are

kno

wn

at

startup,

messages

can

also,

where

p

ossible,

b

e

directly

routed

o

v

er

custom

task-to-task

c

hannels.

3.4.3

Virtual

T

op

ology

On

the

other

hand,

although

MPI

do

es

not

ha

v

e

a

concept

of

a

virtual

mac

hine,

MPI

do

es

pro

vide

a

higher

lev

el

of

abstraction

on

top

of

the

computing

resources

in

terms

of

the

message-

passing

top

ology

.

In

MPI

a

group

of

tasks

can

b

e

arranged

in

a

sp

eciØc

logical

in

terconnection

top

ology

[NS02,

F

or94]

.

A

virtual

top

ology

is

a

mec

hanism

for

naming

the

pro

cesses

in

a

group

in

a

w

a

y

that

Øts

the

comm

unication

pattern

b

etter.

The

main

aim

of

this

is

to

mak

e

subsequen

t

co

de

simpler.

It

ma

y

also

pro

vide

hin

ts

to

the

run-time

system

whic

h

allo

w

it

to

optimize

the

comm

unication

or

ev

en

hin

t

to

the

loader

ho

w

to

conØgure

the

pro

cesses.

F

or

example,

if

our

pro

cesses

will

comm

unicate

mainly

with

nearest

neigh

b

ours

after

the

fashion

of

a

t

w

o-dimensional

grid

(see

Figure

3),

w

e

could

create

a

virtual

top

ology

to

re∞ect

this

fact.

What

w

e

gain

from

this

creation

is

access

to

con

v

enien

t

routines

whic

h,

for

example,

compute

the

rank

of

an

y

pro

cess

giv

en

its

co

ordinates

in

the

grid,

taking

prop

er

accoun

t

of

b

oundary

conditions.

In

particular,

there

are

routines

to

compute

the

ranks

of

our

nearest

neigh

b

ours.

The

rank

can

then

b

e

used

as

an

argumen

t

to

message{passing

op

erations.

10

1 answer