c++ - OpenGL program lags every now and then -

c++ - OpenGL program lags every now and then -

i using c++ sdl 2, opengl 3.3, windows 8. whenever run program, time takes draw each frame usually< 1 ms, drawing few hundred quads. batched drawing, , have same texture. not querying gpu. have tried calling glflush() @ end of every frame. every 1 time in while, time takes draw jumps 3-5 ms. jumps 30 ms. can prepare this?

void xl::spritebatch::render() { generateelements(); glbuffersubdata(gl_array_buffer, 0, vertexcount * 8 * sizeof(vertexbuffer[0]), vertexbuffer.data()); glbuffersubdata(gl_element_array_buffer, 0, eboffset * sizeof(elementbuffer[0]), elementbuffer.data()); gldrawelements(gl_triangles, vertexcount / 4 * 6, gl_unsigned_int, 0); vertexbuffer.clear(); elementbuffer.clear(); vertexcount = 0; eboffset = 0; }

c++ opengl