multithreading - Parallel, but slower -

-

I am using Monte Carlo method to calculate PE and make a basic experience with parallel programming and OpenMP I want to

The problem is that when I use 1 thread, x iterations always run faster than n thread, x iterations. Can anyone tell me?

For example the code runs like "a.out 1 1000000", where there are 1 thread and 1000000 iterations 

  include  using namespace std; Int main (int argc, char * argv []) {double arrow_area_circle, pi; Float xp, yp; Int i, n; Double Pitting = Ethan (1.0) * 4.0; // pi for error cout & lt; & Lt; "Number Processor:" & lt; & Lt; Omp_get_num_procs () & lt; & Lt; Endl; // Number of divisions Iersarions = atoi (argv [2]); Arrow_area_circle = 0.0; #pragma omp parallel number_read (eto (argv [1])) {srandom (omp_get_thread_num ()); To reduce personal (XP, YP) ​​#pragma omp (+: arrow_area_circle) for // *, /, -, + (i = 0; i  
 If you do more work then a CPU intensive task will be slow in this way Threads in comparison to the CPU in the system If you are running it on a CPU system, you can of course see slowdown with more than one thread. This is due to the OS to switch between different threads - it's a pure overhead. Ideally this kind of thread should work as a core. 
 
 Another issue is that arrow_area_circle has been shared between Threads. If you have a thread running on each core, then increasing the arrow arrow_area_circle will cancel the copy in the other core's cache, which will refresh them. Arrow_area_circle ++ Whatever cycle you should take, take dozens or hundreds of cycles. 
 
 EDIT: Joe Duffy posted at the cost of sharing data between threads.

Comments

Post a Comment

Popular posts from this blog

asp.net - Javascript/DOM Why is does my form not support submit()? -

-
This is my first time working with asp.net and javascript, so I do not know very good web resources, or Much about javascript debugging I have to find out that on line oFormObject.submit (); Microsoft JScript Runtime Error: Object does not support this property or method I am using the link to work as a button because I am terrible in aesthetics and I think That link will look more professional than a table of 50 buttons. I have read that this solution can cause problems with browsers due to pre-rendering of my links and many additional traffic and problems, but CSS gives me a button like a link, which has issues of alignment and difference seemed to. & lt ;! DOCTYPE HTML PUBLIC "- // W3C // DTD HTML 4.01 // N" "http://www.w3.org/TR/html4/strict.dtd"> & Lt; Html xmlns = "http://www.w3.org/1999/xhtml" & gt; & Lt; Head & gt; & Lt; Link rel = "stylesheet" type = "text / css" href = "defect differen
Read more

sockets - Delphi: TTcpServer, connection reset when reading -

-
I am trying to implement one for Delphi, but there are some problems with communication. Fitnesse will start my process, and give me a portmember as a command line argument. Then I should make a socket on the port number given to me, and fitness will connect to that port I am using a TCPCP server for the job: < Pre> TcpServer1.LocalPort: = ParamStr (ParamCount); TcpServer1 Active: = true; On OnEXEPT () -Event, I send the protocol version to use as specified in the protocol. Process TForm1.TcpServer1Accept (From: TOBject; ClientSocket: TCustomIpClient); Var s: ansistring; Start clientSocket. Syndrome ('slim - v 0.0', # 10); SetLength (S, 6); ClientSketts Receavebook (S, 6); End; When I call ReceiveBuf (), the process ends, and fitness throws an exception: java.net.SocketException: connection Reset I have seen what sent and received. It shows that my code sends the protocol version, fitness sends back a message, and when I try to get this message
Read more

javascript - Classic ASP "ExecuteGlobal" statement acting differently on two servers -

-
I have a strange problem that I really do not know. In addition to developing a new ASP.NET site, I have to support the old "classic ASP" site. It is written in VBScript with a batch of JavaScript functions. Many of the JavaScript functions include 'files' Everything is fine on our production system (which security is controlled by another group - this is a military installation) Debugging them once did not work I). However, I have a fix for a vague bug that needs to be fully tested and some functions do not run under the "local" copy of the website that runs on my PC. For the record, I am running IIS 5.1 on XP. The problem is that some Javascript functions are running "OK" on the production server, but when they use it as a server, they are not defined on my PC what is happening that last Programmer, for some reason, has decided to put some functions in a series of files, which according to the observations, imitate the "need_once
Read more