From: Gang Zhao (galaxy_at_cs.washington.edu)
Date: Wed Jan 14 2004 - 21:52:17 PST
The exokernal (Xok) system is pretty exciting. It is a rewrite of parts of the unix kernel to push the boundary of kernel transitions down farther.
It's based upon all running applications on a system compiling against (exo)kernel libraries, such that kernel transitions are not necessary for major portions of what would ordinarily be kernel calls. In particular resource allocation (management) appears to be done by the exokernel library, while resource protection is done by the kernel.
In particular this means that the protection ends up being done on disk pages and their memory representations. This required writing a new file system.
This does in theory allow for much finer grain control of system resource allocation and use by applications. (cache allocation was the example used in the paper).
The authors seem to have thought through a number of the protection issues regarding spoofing of the libOS and crashes.
In particular for the resource hungry Cheetah web server this produced tremendous gains in performance.
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