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We assume that your program runs correctly. It would be rather ridiculous to time a program that’s not running right, though this doesn’t mean it doesn’t happen. Depending on what you are doing, you may be interested in knowing how much time is spent overall, or you may be looking at just a portion of the program. We show you how to time the whole program first, and then talk about timing individual loops or subroutines.

Timing a whole program

Under UNIX, you can time program execution by placing the time command before everything else you normally type on the command line. When the program finishes, a timing summary is produced. For instance, if your program is called foo , you can time its execution by typing time foo . If you are using the C shell or Korn shell, time is one of the shell’s built-in commands. With a Bourne shell, time is a separate command executable in /bin . In any case, the following information appears at the end of the run:

  • User time
  • System time
  • Elapsed time

These timing figures are easier to understand with a little background. As your program runs, it switches back and forth between two fundamentally different modes: user mode and kernel mode . The normal operating state is user mode. It is in user mode that the instructions the compiler generated on your behalf get executed, in addition to any subroutine library calls linked with your program. Cache miss time is buried in here too. It might be enough to run in user mode forever, except that programs generally need other services, such as I/O, and these require the intervention of the operating system — the kernel. A kernel service request made by your program, or perhaps an event from outside your program, causes a switch from user mode into kernel mode.

Time spent executing in the two modes is accounted for separately. The user time figure describes time spent in user mode. Similarly, system time is a measure of the time spent in kernel mode. As far as user time goes, each program on the machine is accounted for separately. That is, you won’t be charged for activity in somebody else’s application. System time accounting works the same way, for the most part; however, you can, in some instances, be charged for some system services performed on other people’s behalf, in addition to your own. Incorrect charging occurs because your program may be executing at the moment some outside activity causes an interrupt. This seems unfair, but take consolation in the fact that it works both ways: other users may be charged for your system activity too, for the same reason.

Taken together, user time and system time are called CPU time . Generally, the user time is far greater than the system time. You would expect this because most applications only occasionally ask for system services. In fact, a disproportionately large system time probably indicates some trouble. For instance, programs that are repeatedly generating exception conditions, such as page faults, misaligned memory references, or floating-point exceptions, use an inordinate amount of system time. Time spent doing things like seeking on a disk, rewinding a tape, or waiting for characters at the terminal doesn’t show up in CPU time. That’s because these activities don’t require the CPU; the CPU is free to go off and execute other programs.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit 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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