Why is the performance for this Java code so inconsistent? -

-

i'm running small test although micro benchmark mimic doing in production pretty well.

i'm creating 2d array, 5 columns , 10,000,000 rows filled random integers between 0-19 inclusive. want sum numbers in 3rd column long value in 2nd column even. 100 times warm , 100 times , time how long takes.

on machine vast majority of time takes around 9 seconds, however, takes under 6 seconds.

it doesn't garbage collection, or jit compilation.

does have idea why faster occasionally?

i run code jdk7u11 on linux these arguments: -server -xx:+printcompilation -xms500m -xmx500m -verbose:gc -xx:+printgctimestamps -xx:+printgcdetails however, using various different jdks (from 6 way 8) , removing these parameters doesn't seem effect timings significantly.

here code:

import java.util.arraylist; import java.util.random;  public class javaperformancetest {     public static void main(string[] args) {         int numcolumns = 5;         int numrows = 10000000;         int[][] data = new int[numcolumns][numrows];         random rand = new random(1234);         (int j = 0; j < numcolumns; j++) {             (int = 0; < numrows; i++) {                 data[j][i] = rand.nextint(20);             }         }         int warmup = 100;         arraylist<integer> sums = new arraylist<integer>();         system.out.println("warm " + warmup + " times");         long warmupstart = system.nanotime();         (int = 0; < warmup; i++) {             sums.add(sum(numrows, data));         }         long warmupend = system.nanotime();         system.out.println("warm complete " + (warmupend - warmupstart) / 1000000);         int numberofruns = 100;         int finalsum = 0;         long starttime = system.nanotime();         (int = 0; < numberofruns; i++) {             finalsum = sum(numrows, data);         }         long endtime = system.nanotime();         long diff = (endtime - starttime) / 1000000;         system.out.println("time taken: " + diff + "    sum: " + finalsum);     }       public static int sum(int numrows, int[][] columnbased) {         int sum = 0;         (int = 0; < numrows; i++) {             if ((columnbased[1][i] % 2) == 0) {                 sum += columnbased[2][i];             }         }         return sum;     } }

thanks, nick.

there number of possible causes slow performance including cache misses , failed branch prediction. make sure code optimal , repeat ensure result stable.

import java.util.arraylist; import java.util.random;  public class javaperformancetest {     public static void main(string[] args) {         int numcolumns = 5;         int numrows = 10000000;         byte[][] data = new byte[numcolumns][numrows];         random rand = new random(1234);         (int j = 0; j < numcolumns; j++) {             (int = 0; < numrows; i++) {                 data[j][i] = (byte) rand.nextint(20);             }         }         int warmup = 10;         arraylist<integer> sums = new arraylist<integer>();         system.out.println("warm " + warmup + " times");         long warmupstart = system.nanotime();         (int = 0; < warmup; i++) {             sums.add(sum(numrows, data));         }         long warmupend = system.nanotime();         system.out.println("warm complete " + (warmupend - warmupstart) / 1000000);         (int t = 0; t < 3; t++) {             int numberofruns = 100;             int finalsum = 0;             long starttime = system.nanotime();             (int = 0; < numberofruns; i++) {                 finalsum = sum(numrows, data);             }             long endtime = system.nanotime();             long diff = (endtime - starttime) / 1000000;             system.out.println("time taken: " + diff + "    sum: " + finalsum);         }     }       public static int sum(int numrows, byte[][] columnbased) {         int sum = 0;         byte[] col1 = columnbased[1];         byte[] col2 = columnbased[2];         (int = 0; < numrows; i++)             // use multiplication instead of "if" avoid branch prediction failures             sum += ((col1[i] + 1) & 1) * col2[i];         return sum;     } }

prints

warm 10 times warm complete 109 time taken: 1006    sum: 47505460 time taken: 1006    sum: 47505460 time taken: 1026    sum: 47505460

in summary: optimising code improve performance far more playing command line parameters.


Popular posts from this blog

How to calculate SNR of signals in MATLAB? -

-
i've encountered simple, yet fundamental problem on calculating snr: there several signals : s1 = original , pure clean signal without noise. n1 = white gaussian noise going added s1. s2 = s1 + n1 (the noisy signal before performing noise-reduction algorithm) s3 = noise-reduced signal (after performing noise reduction algorithm) n2 = s3 - s1 (the amount of noise after performing noise-reduction algorithm) now want compare snr before , after performing noise-reduction algorithm. which signals should consider snr_before!? s1/n1 or s2/n1 ? which signals should consider snr_after!? s3/n1 or s3/n2 ? which commands or functions should use in matlab in order compute snr_before , snr_after? thanks billion putting time on helping me. what know calculating snr before : snrbeforenoise = mean( signal .^ 2 ) / mean( noise .^ 2 ); and snr after : residual_noise = signal - noise_reduced_signal; snr_after = mean( signal .^ 2 ) / mean( residual_noise .^ 2...
Read more

c# - Attempting to upload to FTP: System.Net.WebException: System error -

-
i have api takes in xml , uploads files based on information in xml. uploads on schedule (also xml), , have tested surrounding , know works. i getting error 40% of time on first file attempt upload in each time cycle (time cycle = 45 minutes files, 30 minutes others). here code upload: try { loggerftp.log("uploading file: " + filename, false); // create request. ftpwebrequest request = (ftpwebrequest)webrequest.create(appsettingsftp.ftpurl + @"/" + filename); request.method = webrequestmethods.ftp.uploadfile; request.timeout = 6000000; //set 100 minutes //request.timeout = -1; //set infinite // add login credentials. request.credentials = new networkcredential(appsettingsftp.ftplogin, appsettingsftp.ftppassword); // grab file contents. streamreader sourcestream = new streamreader(appsettingsftp.uploadfiledirectory + filename); byte[] filecontents = encoding.utf8.getbytes(sourcestream.readtoend()); sourcest...
Read more

ios - UISlider customization: how to properly add shadow to custom knob image -

-
Image
i need place custom knob image shadow uislider. far have image of 38x38, of there region defines shadow of knob. now while using image, when slide knob extreme ends actual knob not able cover end points, hence end points visible under transparent region of knob image this code using customize uislider uiimage *slidebtimg = [uiimage imagenamed:sliderknobimg]; [self.ratingslider setthumbimage:slidebtimg forstate:uicontrolstatenormal]; [self.ratingslider setthumbimage:slidebtimg forstate:uicontrolstatehighlighted]; how can implement custom knob shadow beneath it, covering end points?? look inside uislider.h , there methods let customize slider knob , track needed. (ios 2.0 , above) // lets subclass lay out track , thumb needed - (cgrect)minimumvalueimagerectforbounds:(cgrect)bounds; - (cgrect)maximumvalueimagerectforbounds:(cgrect)bounds; - (cgrect)trackrectforbounds:(cgrect)bounds; - (cgrect)thumbrectforbounds:(cgrect)bounds trackrect:(cgrect)rect value:...
Read more