Subject: Re: context overflow

From: Cort Dougan <[email-masked]>
Date: Thu, 8 Feb 2001 15:26:42 -0700

} statements about which VMM design is best.  You can create a wonderful
} engineer solution, but are you solving the problem or simply masking a
} symptom?

Would you characterize AIX as an OS that takes advantage of the VMM design
of the PowerPC?  From the benchmarks I did it appeared to suffer the same
problem that Linux/PPC did at that time.  The problem being, a
straightforward implementation of the software side of the VM design of the
PowerPC.  After some general improvements in the MM system of Linux/PPC we
sped things up by a large amount by doing what you claim is a mistake.  We
widened the gap between Linux/PPC and what was probably the best example of
what VM design can come from knowledge of the PPC architecture (in AIX).

AIX can't claim to be doing it better.  I was unable to look under the hood
of AIX, of course, but my benchmarks did show that the _ONLY_ thing that
mattered - wall clock time of user apps - was improved.  Doing things that
non-PPC way is not a flaw if it results in better performance.

I do stand by our design, and the choices we made, but I'm open to
suggestion for better ways to do it.  I can certainly believe there's a lot
of room for improvement.  This is linux, though - actual working code speaks
more loudly and clearly than anything else.

Do you have an example of a better way of doing a VM system in Linux/PPC?
We can't change the page table layout.  That's something we're stuck with,
in one form or another, in Linux no matter what (not our decision).  What
does Kitchewan do for a VM subsystem?  Can you give me an overview of the
design?

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