Databases
StackOverflow2013
Postsdbo
POMultiple instances of program on multi-core machine
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POMultiple instances of program on multi-core machine
    primarykey
    data
    text
    <p>I am assuming a dual-core (2 cores per processors) machine with 2 processors for the questions that follow; so a total of 4 "cores". So some natural questions arose: </p> <ol> <li><p>Suppose I wrote a simple serial program and built it in, say, Visual Studio.. and ran the same program twice, say, with distinct input data in each run. Would they be running on the same processor? Or distinct processors? How much RAM memory would be assigned to each? Would it be the RAM memory on 1 processor (2 cores) or the total RAM? I believe the two programs would run on distinct processors and should each have RAM memory of 1 processor (2 cores); but I am not 100% certain. Would the behavior be any different on Linux?</p></li> <li><p>Now suppose my program was written using a distributed memory parallel interface such as MPI and that I ran it once with 2 processors in the np argument (say). Would the program use both processors (and in effect all 4 cores)? Is this the optimal value for the argument -np? In other words, if I did the same with -np 3 or -np 4; is it correct to assume there would be no added advantage? Again, I think so, but I am not 100% certain. I assume also that I could go higher than 4 (-np 5, -np 6, etc). In such cases, how do the processes compete for memory at values of np > 4? Would the performance get worse for np > 4. I think yes, and perhaps this partly depends on problem size, but again not 100% sure.</p> <p>Next, suppose I ran two instances of my MPI-built parallel program, both with -np 2, each with, say, different input data. First off, is this possible? I assume it is and that they each run on both processors? How are the two programs synchronized and how do they individually compete for memory sequentially? This should atleast in part, be based on the order of launching the programs, presumably?</p></li> <li><p>Lastly, suppose my program was written using a shared memory parallel interface such as OpenMP and that I ran it once. How many "threads" can I run it on to make full use of shared memory parallelism - is it 2 or 4? (since I have 2 processors with 2 cores each). My guess is it is 4; since all 4 cores are part of the a single shared memory unit? Is that correct? If the answer is 4; does it make sense to run on greater than 4 threads? I am not sure this even works (unlike MPI, where I believe we can do -np 5, -np 6 and so on).</p></li> </ol> <p>Finally, suppose I run 2 instances of the shared memory parallel program, each with, say, different input data. I assume this is possible and that the individual processes would somehow compete for memory, presumably in the order the programs were launched?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USLightness Races in Orbit
    1. USsquashed.bugaboo
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POMultiple instances of program on multi-core machine
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POMultiple instances of program on multi-core machine
      1. USAndré Puel
      1. VTFavorite
    3. VO
      singulars
      1. POMultiple instances of program on multi-core machine
      1. This table or related slice is empty.
      1. VTUpMod
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload