C# Confusing Results from Performance Test
- by aip.cd.aish
I am currently working on an image processing application. The application captures images from a webcam and then does some processing on it. The app needs to be real time responsive (ideally < 50ms to process each request). I have been doing some timing tests on the code I have and I found something very interesting (see below).
clearLog();
log("Log cleared");
camera.QueryFrame();
camera.QueryFrame();
log("Camera buffer cleared");
Sensor s = t.val;
log("Sx: " + S.X + " Sy: " + S.Y);
Image<Bgr, Byte> cameraImage = camera.QueryFrame();
log("Camera output acuired for processing");
Each time the log is called the time since the beginning of the processing is displayed. Here is my log output:
[3 ms]Log cleared
[41 ms]Camera buffer cleared
[41 ms]Sx: 589 Sy: 414
[112 ms]Camera output acuired for processing
The timings are computed using a StopWatch from System.Diagonostics.
QUESTION 1
I find this slightly interesting, since when the same method is called twice it executes in ~40ms and when it is called once the next time it took longer (~70ms).
Assigning the value can't really be taking that long right?
QUESTION 2
Also the timing for each step recorded above varies from time to time. The values for some steps are sometimes as low as 0ms and sometimes as high as 100ms. Though most of the numbers seem to be relatively consistent.
I guess this may be because the CPU was used by some other process in the mean time? (If this is for some other reason, please let me know)
Is there some way to ensure that when this function runs, it gets the highest priority? So that the speed test results will be consistently low (in terms of time).
EDIT
I change the code to remove the two blank query frames from above, so the code is now:
clearLog();
log("Log cleared");
Sensor s = t.val;
log("Sx: " + S.X + " Sy: " + S.Y);
Image<Bgr, Byte> cameraImage = camera.QueryFrame();
log("Camera output acuired for processing");
The timing results are now:
[2 ms]Log cleared
[3 ms]Sx: 589 Sy: 414
[5 ms]Camera output acuired for processing
The next steps now take longer (sometimes, the next step jumps to after 20-30ms, while the next step was previously almost instantaneous). I am guessing this is due to the CPU scheduling. Is there someway I can ensure the CPU does not get scheduled to do something else while it is running through this code?
