Performance of system/dos function
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[status, cmdout] = system(cmd)
has been reported to be slow for a while (see this and this), but there seems no satisfying solution yet.
Here is what I tested for Windows command reg.exe, trying to figure out a workaround.
cmd = 'reg.exe query HKEY_LOCAL_MACHINE\HARDWARE /s'; % as an example
tic; [status, cmdout] = system(cmd); toc
Elapsed time is 3.517736 seconds.
whos cmdout
Name Size Bytes Class Attributes
cmdout 1x95249 190498 char
tic; [status, cmdout] = dos(cmd); toc
Elapsed time is 3.512847 seconds.
tic; cmdout = evalc(['! ' cmd]); toc
Elapsed time is 3.509961 seconds.
As we can see, system(), dos() and evalc('!') have similar performance. When I test the same cmd in other programs (Octave and python), it takes about 0.6 to 0.7 seconds. Running it at Windows command prompt takes less than a second based on my eye test. Then I tried to redirect output to a file:
tic; [status, cmdout] = system([cmd ' >myFile']); toc
Elapsed time is 0.886915 seconds.
This improves the performance significantly. The cmdout is empty now as expected.
Does this suggest there should be a way to improve system() for dealing with cmdout?
Is there a way to redirect cmdout to a Matlab string, so we can avoid to read and delete the temp file?
7 个评论
Horshack Horshack
2021-4-20
I'm having the same issue. To demonstrate, I wrote a simple C program 'printstdout' that prints the number of characters it's been told to via a command line argument:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* argv[]) {
int numCharsToPrint = argc >= 2 ? atoi(argv[1]) : 0;
int numCharsPrintedThisLine;
numCharsPrintedThisLine = 0;
while (numCharsToPrint-- > 0) {
printf("*");
if (++numCharsPrintedThisLine == 78) {
numCharsPrintedThisLine = 0;
if (numCharsToPrint-- > 0)
printf("\n");
}
}
return 0;
}
And tested it with the following script:
numChars = uint32(1);
while (numChars <= 2^20)
fprintf("numChars = %7d: ", numChars);
tic; [exitCode, output] = system(['printstdout ' num2str(numChars)]); toc;
numChars = numChars*2;
end
Here's the output for Matlab:
numChars = 1: Elapsed time is 0.035415 seconds.
numChars = 2: Elapsed time is 0.034140 seconds.
numChars = 4: Elapsed time is 0.033591 seconds.
numChars = 8: Elapsed time is 0.034396 seconds.
numChars = 16: Elapsed time is 0.033863 seconds.
numChars = 32: Elapsed time is 0.033824 seconds.
numChars = 64: Elapsed time is 0.033170 seconds.
numChars = 128: Elapsed time is 0.033617 seconds.
numChars = 256: Elapsed time is 0.033296 seconds.
numChars = 512: Elapsed time is 0.034161 seconds.
numChars = 1024: Elapsed time is 0.032989 seconds.
numChars = 2048: Elapsed time is 0.033904 seconds.
numChars = 4096: Elapsed time is 0.602469 seconds.
numChars = 8192: Elapsed time is 0.703521 seconds.
numChars = 16384: Elapsed time is 0.903753 seconds.
numChars = 32768: Elapsed time is 1.304120 seconds.
numChars = 65536: Elapsed time is 2.105577 seconds.
numChars = 131072: Elapsed time is 3.708676 seconds.
numChars = 262144: Elapsed time is 6.916353 seconds.
numChars = 524288: Elapsed time is 13.246939 seconds.
numChars = 1048576: Elapsed time is 26.452178 seconds.
And here is the output from Octave:
numChars = 1: Elapsed time is 0.0197449 seconds.
numChars = 2: Elapsed time is 0.0113029 seconds.
numChars = 4: Elapsed time is 0.0113032 seconds.
numChars = 8: Elapsed time is 0.0113418 seconds.
numChars = 16: Elapsed time is 0.011956 seconds.
numChars = 32: Elapsed time is 0.010741 seconds.
numChars = 64: Elapsed time is 0.011215 seconds.
numChars = 128: Elapsed time is 0.0108809 seconds.
numChars = 256: Elapsed time is 0.011487 seconds.
numChars = 512: Elapsed time is 0.010798 seconds.
numChars = 1024: Elapsed time is 0.012202 seconds.
numChars = 2048: Elapsed time is 0.0105009 seconds.
numChars = 4096: Elapsed time is 0.0121739 seconds.
numChars = 8192: Elapsed time is 0.01156 seconds.
numChars = 16384: Elapsed time is 0.0121598 seconds.
numChars = 32768: Elapsed time is 0.0127161 seconds.
numChars = 65536: Elapsed time is 0.014755 seconds.
numChars = 131072: Elapsed time is 0.0170429 seconds.
numChars = 262144: Elapsed time is 0.023046 seconds.
numChars = 524288: Elapsed time is 0.0346019 seconds.
numChars = 1048576: Elapsed time is 0.0581162 seconds.
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