[coyotos-dev] Hi + some stuff I found researching

[Jonathan S. Shapiro]

On Wed, 2006-07-12 at 16:53 -0400, Haplo wrote:
> A: Software feedback based scheduling. This seems like a good idea to  
> me. Priority based scheduling is just too limiting, and in the end it  
> all ends up "best guess" or the more common case is that most non-OS  
> associated apps are all given the same priority...

Yes, and software-based feedback is extremely attractive. The problem
with it is that it provides all applications with an unauthorized
communication channel.

We definitely need to look at this. I just wanted to point out that it's
not a simple thing to do in a secure and robust system.

> B:Executable data structures. This has limited use but could still  
> provide improvement. In this case it would be more like instantiating  
> an object than dynamically generating code. The most specific example  
> of where this might be useful - that I can give at least - would be  
> capability register pages. If a page can only hold a certain number  
> of indices, then in-lined code that "knows" about the capabilities  
> it's managing could traverse them quickly and return the capability  
> at the selected index....

Remember that the capability pages are *disk* data structures....

If you look at the HDTrans work, you will find that we know about
executable data structures. Sometimes its a good thing, sometimes not.
For the HDTrans sieve, it was a huge win.

The problem is that the benefit for this type of data structure tends to
be *extremely* dependent on the target CPU. Executable structures make
great sense on IA-32 mainly because they let you avoid changes to
condition codes (which are expensive). On other architectures, the case
for them is much less clear.

> C:Something not really synthesis related that I didn't mention  
> earlier for various reasons. A self-healing layer like in Minix-3.

In 30 years of operating KeyKOS and EROS, we have yet to observe any
real case that motivated a healing layer. The right thing to do is fix
the code.

Separately, you should know that Minix doesn't deserve credit for this
idea. It's a *very* old idea. Goes back to at least 1957 that I know
about.

shap