[coyotos-dev] For your amusement

[Jonathan S. Shapiro]

On Wed, 2007-09-26 at 00:05 +0200, Jeroen Visser wrote:
> Very, very cool. Congratulations!
> 
> It seems to require 6MB RAM at least now. Startup delay is significant
> when more memory is added: 32MB => 3secs, 64MB => 6s, 256MB => 13s
> (under QEMU at least).

Yes. Actually there are two separate issues here:

1. Why 6M?  I don't know, and I would like to find out. I *suspect* it
has to do with the way that we pre-allocate page tables, but I do not
know. Can you tell me what diagnostic appears when you attempt to boot
with less?

2. Startup delay. I suspect the root cause of this is that we are
initializing all of object space eagerly, and that we are using
temporary mappings to do that. The temporary mappings need to be
invalidated fairly often, and QEMU is very slow at that. We need to
confirm whether this is true.

One way to do that is to run under GDB and hit ^c a couple of times
during that delay. Do a back-trace ("bt") and you will probably find
that some procedure call is driving all of this. If someone can identify
that procedure, it would be a big help.

We can find it, of course, but it will take time and it isn't a top
priority right now. If you can help us narrow the search, it becomes a
lot easier to fix it.

shap