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Assertions also let you choose subroutines that you think are good candidates for inlining. However, subject to its thresholds, the compiler may reject your choices. Inlining could expand the code so much that increased memory activity would claim back gains made by eliminating the procedure call. At higher optimization levels, the compiler is often capable of making its own choices for inlining candidates, provided it can find the source code for the routine under consideration.

Some compilers support a feature called interprocedural analysis . When this is done, the compiler looks across routine boundaries for its data flow analysis. It can perform significant optimizations across routine boundaries, including automatic inlining, constant propagation, and others.

No side effects

Without interprocedural analysis, when looking at a loop, if there is a subroutine call in the middle of the loop, the compiler has to treat the subroutine as if it will have the worst possible side effects. Also, it has to assume that there are dependencies that prevent the routine from executing simultaneously in two different threads.

Many routines (especially functions) don’t have any side effects and can execute quite nicely in separate threads because each thread has its own private call stack and local variables. If the routine is meaty, there will be a great deal of benefit in executing it in parallel.

Your computer may allow you to add a directive that tells you if successive sub-routine calls are independent:


C$ASSERT NO_SIDE_EFFECTS DO I=1,NCALL BIGSTUFF (A,B,C,I,J,K) END DO

Even if the compiler has all the source code, use of common variables or equivalences may mask call independence.

Manual parallelism

At some point, you get tired of giving the compiler advice and hoping that it will reach the conclusion to parallelize your loop. At that point you move into the realm of manual parallelism. Luckily the programming model provided in FORTRAN insulates you from much of the details of exactly how multiple threads are managed at runtime. You generally control explicit parallelism by adding specially formatted comment lines to your source code. There are a wide variety of formats of these directives. In this section, we use the syntax that is part of the OpenMP (see [link] ) standard. You generally find similar capabilities in each of the vendor compilers. The precise syntax varies slightly from vendor to vendor. (That alone is a good reason to have a standard.)

The basic programming model is that you are executing a section of code with either a single thread or multiple threads. The programmer adds a directive to summon additional threads at various points in the code. The most basic construct is called the parallel region .

Parallel regions

In a parallel region, the threads simply appear between two statements of straight-line code. A very trivial example might be the following using the OpenMP directive syntax:


PROGRAM ONE EXTERNAL OMP_GET_THREAD_NUM, OMP_GET_MAX_THREADSINTEGER OMP_GET_THREAD_NUM, OMP_GET_MAX_THREADS IGLOB = OMP_GET_MAX_THREADS()PRINT *,’Hello There’ C$OMP PARALLEL PRIVATE(IAM), SHARED(IGLOB)IAM = OMP_GET_THREAD_NUM() PRINT *, ’I am ’, IAM, ’ of ’, IGLOBC$OMP END PARALLEL PRINT *,’All Done’END

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
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Source:  OpenStax, High performance computing. OpenStax CNX. Aug 25, 2010 Download for free at http://cnx.org/content/col11136/1.5
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