Hi there,
thanks for the opportunity that you give us to write on this mailing-list.
I'm am playing with the Vector API bundled in Java 22 and wow, they are
amazing.
I have some serious benefits using them even for simple tasks on my AMD
Ryzen 9 7950X3D CPU that uses Zen4 architecture.
Can't wait to see how bigger the benefits will be on the upcoming
processors that has some serious optimized AVX512 instructions (AMD Zen5
architecture and Intel AV10 instructions).
I'll try to give you some context.
I am writing an open source software that is basically a free clone of
the Philips Ambilight effect.
What is it?
Basically you put a LED strip behind your monitor/TV, the software
capture the screen,
it calculates the average colors of your screen, and sends those average
values to a microcontroller (arduino) that drives the strip and light up
the LEDs accordingly.
This effect is also known as dynamic bias light.
More info here if you are curious:
https://github.com/sblantipodi/firefly_luciferin
Most of the computations involved are on the GPU side but some intensive
ones are on the CPU side.
Let's go deeper on the Vector API.
GPU acquire the screen image 60 times per seconds (or even more), every
frame is a Buffer that contains colors information for each pixel of the
frame.
This buffer is a Java Direct IntBuffer that doesn't have a corresponding
array inside the heap for performance reason.
Once I have this IntBuffer I need to calculate the average colors of the
screen and this thing can be made on the fly on the IntBuffer without
copying the IntBuffer inside an Array. This kind of copy is really
really heavy and degrade performance.
Just a snippet that shows it without using the Vector API...
for (int y =0; y < pixelInUseY; y++) {
for (int x =0; x < pixelInUseX; x++) {
int offsetX = (xCoordinate + x);
int offsetY = (yCoordinate + y);
int bufferOffset = (Math.min(offsetX,widthPlusStride)) + ((offsetY
<height) ? (offsetY *widthPlusStride) : (height *widthPlusStride));
int rgb =rgbBuffer.get(Math.min(rgbBuffer.capacity() -1, bufferOffset));
r += rgb >>16 &0xFF;
g += rgb >>8 &0xFF;
b += rgb &0xFF;
pickNumber++;
}
}
leds[key -1] = ImageProcessor.correctColors(r, g, b, pickNumber);
Now I'm trying to use the Vector API to accelerate this computations
even more and hey, it worked awesome.
Using AVX512 (Species512) the computations is 40%-80% faster than
without the Vector API.
int firstLimit;
int secondLimit;
// Processing the buffer in the correct order is crucial for SIMD
performance if (pixelInUseX < pixelInUseY) {
firstLimit = pixelInUseX;
secondLimit = pixelInUseY;
}else {
firstLimit = pixelInUseY;
secondLimit = pixelInUseX;
}
// SIMD iteration for (int x =0; x < firstLimit; x++) {
for (int y =0; y < secondLimit; y +=
MainSingleton.getInstance().SPECIES.length()) {
int offsetX;
int offsetY;
if (pixelInUseX < pixelInUseY) {
offsetX = (xCoordinate + x);
offsetY = (yCoordinate + y);
}else {
offsetX = (xCoordinate + y);
offsetY = (yCoordinate + x);
}
int bufferOffset = (Math.min(offsetX,widthPlusStride)) + ((offsetY
<height) ? (offsetY *widthPlusStride) : (height *widthPlusStride));
// Load RGB values using SIMD int[] rgbArray =new
int[MainSingleton.getInstance().SPECIES.length()];
rgbBuffer.position(bufferOffset);
rgbBuffer.get(rgbArray,0,
Math.min(MainSingleton.getInstance().SPECIES.length(),rgbBuffer.remaining()));
IntVector rgbVector =
IntVector.fromArray(MainSingleton.getInstance().SPECIES, rgbArray,0);
r += rgbVector.lane(0) >>16 &0xFF;
g += rgbVector.lane(1) >>8 &0xFF;
b += rgbVector.lane(2) &0xFF;
pickNumber++;
}
}
leds[key -1] = ImageProcessor.correctColors(r, g, b, pickNumber);
The computation itself is at least ten times faster but at the end it's
only 40%-80% faster because I'm not able to process the IntBuffer on the
fly using Vector API.
As you can see in the previous snippet I need to copy part of the
IntBuffer into an int[] array and then process it using the Vector API.
This copy alone is the thing that requires more time.
Is it possible to process a direct IntBuffer with the Vector API without
loosing time in an array copy?
Thank you for this wonderful API.
Kind regards
Davide
