[Vm-dev] Making a Slower VM

[tim Rowledge]

On 09-02-2014, at 10:07 AM, David T. Lewis <lewis at mail.msen.com> wrote:
> Joking aside, there actually is one legitimate reason for wanting a slow VM.
> With high performance VMs and with ever faster hardware, it is very easy to
> implement sloppy things in the image that go unnoticed until someone runs the
> image on an old machine or on limited hardware. It is sometimes useful to
> test on old hardware or on a slow VM to check for this.

The cheapest and easiest way to do it these days is to buy a Raspberry Pi. You’ll learn very quickly where you have used crappy algorithms or poor technique… though of course you do have to put up with X windows as well. Unless you try RISC OS, which although not able to make the raw compute performance faster at least has a window system that doesn’t send every pixel to the screen via Deep Space Network to the relay on Sedna.

> I think someone mentioned it earlier, but a very easy way to produce an
> intentionally slow VM is to generate the sources from VMMaker with the
> inlining step disabled. The slang inliner is extremely effective, and turning
> it off produces impressively sluggish results.

Does that actually work these days? Last I remember was that turning inlining off wouldn’t produce a buildable interp.c file. If someone has had the patience to make it work then I’m impressed.


tim
--
tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
Strange OpCodes: SDLI: Shift Disk Left Immediate