How effective would it be to have the monitor just take a quick sampling of
various locations on the page and test them for the "need" to use one method
over the other...... or is this asking too much of the project code?
Drew Northup, N1XIM
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
Behalf Of Kevin P. Lawton
Sent: Monday, June 12, 2000 3:09 PM
To: [EMAIL PROTECTED]
Subject: Re: Another plex86 technical thing
Ramon van Handel wrote:
> Sounds like a difficult choice -- I'm not so much worried about
> self-modifying code (it's BOUND to be slow, even on a REAL x86)
> but about shared code/data pages (most compilers don't do this,
> but you see this a lot with hand-written assembly, and that just
> may be the way the tightest loops in the kernel are coded.)
>
> I guess the best choice typically depends on the code you run in
> the VM. As we do not know this in advance, I guess it would be
> possible to change policy dynamically, using considerations such
> as
> - What is the relative frequency of data access vs. execute access
> - What part of the page is used for data/code
> - How much longer would it take to re-scan all the code, compared
> to the time a write fault takes?
Very much agreed. It seems to be a hard equation to
make a good call on without some real measurements.
For now, I'll just code it one way. I think you're right
that we may have to implement some instrumentation into
the vcode cache and make dynamic choices as the data
is aquired.
If we don't ultimately have some dynamic flexibility,
we may pay with performance. For now, one static
method will do.
-Kevin
