The minimal code that shows the issue:
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <GL/gl.h>
#include "stdio.h"
// Texture upload time over PCI-E 3 x16
// Tex size: old -> with ReBAR to full GPU memory
// 8k x 4k: 20 ms -> 70 ms
// 8k x 8k: 40 ms -> 140+ ms
enum
{
lWidth = 8192,
lHeight = 8192,
};
const PIXELFORMATDESCRIPTOR pfd =
{
sizeof(PIXELFORMATDESCRIPTOR),
1,
PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
PFD_TYPE_RGBA,
24,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
PFD_MAIN_PLANE,
0, 0, 0, 0
};
int main(void)
{
HWND hWnd = CreateWindowExW(0, L"STATIC", NULL, WS_POPUP, 0, 0, 1, 1, NULL, NULL, NULL, NULL);
HDC hDC = GetDC(hWnd);
SetPixelFormat(hDC, ChoosePixelFormat(hDC, &pfd), &pfd);
HGLRC hGLRC = wglCreateContext(hDC);
wglMakeCurrent(hDC, hGLRC);
GLuint Texture;
glGenTextures(1, &Texture);
void *data = VirtualAlloc(NULL, lWidth*lHeight*4, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
LARGE_INTEGER pfreq, pcount, pcount2;
QueryPerformanceFrequency(&pfreq);
for (int i = 0x10; i--;)
{
QueryPerformanceCounter(&pcount);
glBindTexture(GL_TEXTURE_2D, Texture);
glTexImage2D(GL_TEXTURE_2D, 1, GL_RGB8, lWidth, lHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, data); // also GL_BGRA
glBindTexture(GL_TEXTURE_2D, 0);
glFinish();
QueryPerformanceCounter(&pcount2);
pcount2.QuadPart -= pcount.QuadPart;
printf("Time: %lli\n", pcount2.QuadPart*1000/pfreq.QuadPart);
}
glDeleteTextures(1, &Texture);
wglMakeCurrent(NULL, NULL);
wglDeleteContext(hGLRC);
ReleaseDC(hWnd, hDC);
DestroyWindow(hWnd);
return 0;
}
