Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Look with this:</p> <pre><code>for(int x = 0; x &lt; 4; ++x) #pragma omp parallel for ordered for(int y = 0; y &lt; 4; ++y) #pragma omp ordered cout &lt;&lt; x &lt;&lt; ',' &lt;&lt; y &lt;&lt; " (by thread " &lt;&lt; omp_get_thread_num() &lt;&lt; ')' &lt;&lt; endl; </code></pre> <p>you have:</p> <pre><code>0,0 (by thread 0) 0,1 (by thread 1) 0,2 (by thread 2) 0,3 (by thread 3) 1,0 (by thread 0) 1,1 (by thread 1) 1,2 (by thread 2) 1,3 (by thread 3) </code></pre> <p>Each thread just has to wait for some <code>cout</code> all the work before can be done in parallel. But with:</p> <pre><code>#pragma omp parallel for ordered for(int x = 0; x &lt; 4; ++x) for(int y = 0; y &lt; 4; ++y) #pragma omp ordered cout &lt;&lt; x &lt;&lt; ',' &lt;&lt; y &lt;&lt; " (by thread " &lt;&lt; omp_get_thread_num() &lt;&lt; ')' &lt;&lt; endl; </code></pre> <p>and</p> <pre><code>#pragma omp parallel for collapse(2) ordered for(int x = 0; x &lt; 4; ++x) for(int y = 0; y &lt; 4; ++y) #pragma omp ordered cout &lt;&lt; x &lt;&lt; ',' &lt;&lt; y &lt;&lt; " (by thread " &lt;&lt; omp_get_thread_num() &lt;&lt; ')' &lt;&lt; endl; </code></pre> <p>the situations is:</p> <pre><code>0,0 (by thread 0) 0,1 (by thread 0) 0,2 (by thread 0) 0,3 (by thread 0) 1,0 (by thread 1) 1,1 (by thread 1) 1,2 (by thread 1) 1,3 (by thread 1) 2,0 (by thread 2) 2,1 (by thread 2) 2,2 (by thread 2) 2,3 (by thread 2) 3,0 (by thread 3) 3,1 (by thread 3) 3,2 (by thread 3) 3,3 (by thread 3) </code></pre> <p>So <code>thread 1</code> has to wait for <code>thread 0</code> to finish all its work, before it can <code>cout</code> the first time, and nearly nothing can be done in parallel.</p> <p>Try adding <code>schedule(static,1)</code> to the collapse-version and it should perform at least as good as the first version does.</p>
    singulars
    1. This table or related slice is empty.
    1. POOpenMP parallelize for construct performance
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USx539
    1. USx539
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POOpenMP parallelize for construct performance
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUndeletion
    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