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Now that we have examined the way shared-memory multiprocessor hardware operates, we need to examine how software operates on these types of computers. We still have to wait until the next chapters to begin making our FORTRAN programs run in parallel. For now, we use C programs to examine the fundamentals of multiprocessing and multithreading. There are several techniques used to implement multithreading, so the topics we will cover include:

  • Operating system–supported multiprocessing
  • User space multithreading
  • Operating system-supported multithreading

The last of these is what we primarily will use to reduce the walltime of our applications.

Operating system–supported multiprocessing

Most modern general-purpose operating systems support some form of multiprocessing. Multiprocessing doesn’t require more than one physical CPU; it is simply the operating system’s ability to run more than one process on the system. The operating system context-switches between each process at fixed time intervals, or on interrupts or input-output activity. For example, in UNIX, if you use the ps command, you can see the processes on the system:


% ps -a PID TTY TIME CMD28410 pts/34 0:00 tcsh 28213 pts/38 0:00 xterm10488 pts/51 0:01 telnet 28411 pts/34 0:00 xbiff11123 pts/25 0:00 pine 3805 pts/21 0:00 elm6773 pts/44 5:48 ansys ...% ps –a | grep ansys 6773 pts/44 6:00 ansys

For each process we see the process identifier (PID), the terminal that is executing the command, the amount of CPU time the command has used, and the name of the command. The PID is unique across the entire system. Most UNIX commands are executed in a separate process. In the above example, most of the processes are waiting for some type of event, so they are taking very few resources except for memory. Process 6773 ANSYS is a commonly used structural-analysis package. seems to be executing and using resources. Running ps again confirms that the CPU time is increasing for the ansys process:


% vmstat 5 procs memory page disk faults cpur b w swap free re mf pi po fr de sr f0 s0 -- -- in sy cs us sy id 3 0 0 353624 45432 0 0 1 0 0 0 0 0 0 0 0 461 5626 354 91 9 03 0 0 353248 43960 0 22 0 0 0 0 0 0 14 0 0 518 6227 385 89 11 0

Running the vmstat 5 command tells us many things about the activity on the system. First, there are three runnable processes. If we had one CPU, only one would actually be running at a given instant. To allow all three jobs to progress, the operating system time-shares between the processes. Assuming equal priority, each process executes about 1/3 of the time. However, this system is a two-processor system, so each process executes about 2/3 of the time. Looking across the vmstat output, we can see paging activity ( pi , po ), context switches ( cs ), overall user time ( us ), system time ( sy ), and idle time ( id ).

Each process can execute a completely different program. While most processes are completely independent, they can cooperate and share information using interprocess communication (pipes, sockets) or various operating system-supported shared-memory areas. We generally don’t use multiprocessing on these shared-memory systems as a technique to increase single-application performance.

Questions & Answers

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
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
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
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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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