[Haskell-beginners] Performance problem with Haskell/OpenGL/GLFW

[Jesper Särnesjö]

On Mon, Mar 11, 2013 at 8:23 AM, Jesper Särnesjö <sarnesjo at gmail.com> wrote:
> I used gfxCardStatus to show which card was in use. When I ran
> test2.c, the system briefly switched to the discrete card. However,
> when I ran Test2.hs, the system kept using the integrated chip the
> whole time. Presumably, the Intel chip lacks a hardware implementation
> of OpenGL 3.2, which causes the system to fall back to a software
> renderer. I then used gfxCardStatus to force the system to *always*
> use the discrete card and - boom! - this time Test2.hs received a
> hardware renderer!
>
> So it seems that the problem is a) Mac OS X-specific, or possibly
> specific to systems with multiple graphics cards, b) related to
> triggering the *switch* to the better graphics card. I don't yet
> understand why the C program triggers a switch, while the Haskell
> program does not, but I'll keep investigating.

I haven't had much time to look at this, unfortunately, but I did
notice one interesting thing: the Haskell program *does* in fact
trigger a switch of graphics cards, just... not as quickly.

To see this, you can check the system console (using Console.app).
Here is what a switch from the integrated card to the discrete one
looks like on my machine:

    3/13/13 12:02:22.486 AM WindowServer[77]: Received display connect
changed for display 0x4272dc0
    3/13/13 12:02:22.548 AM WindowServer[77]: Received display connect
changed for display 0x3f003d
    3/13/13 12:02:22.549 AM WindowServer[77]: CGXMuxAcknowledge:
Posting glitchless acknowledge
    3/13/13 12:02:22.593 AM WindowServer[77]: Received display connect
changed for display 0x4272dc0

When I run the C program, this get logged immediately following the
execution of glfwOpenWindow (I stepped through the program using GDB).

For the Haskell program, well... If I run the program normally, the
above gets logged with roughly a second's delay, and the program
receives a software renderer. However, if I step through it using
GHCi, it gets logged immediately following the execution of
glfwOpenWindow - and the program receives a hardware renderer!

Shot in the dark here, but could this be due to lazy I/O? I seem to
recall reading something about GHCi forcing stricter I/O.

-- 
Jesper Särnesjö
http://jesper.sarnesjo.org/