Experience with K42, an open- source, Linux-compatible, scalable operation-system kernel IBM SYSTEM JOURNAL, VOL 44 NO 2, 2005 J. Appovoo 、 M. Auslander 、 M. Butrico 、 D. M. da Silva O. Krieger 、 M. F. Mergen 、 M. Ostrowski 、 B. Rosenburg 、 R. W. Wisniewski 、 J. Xenidis

About K42 Operating-system kernel Open-source Linux-compatible Scalable Being used for rapid prototyping of OS policies and mechanisms.

Main goals Scalability / performance Adaptability Extensibility / maintainability Open-source compatibility

Goal 1. Scalability / performance Being structured in an object-oriented manner. Run efficiently on a range of mulitprocessors and applications. Each resource is managed by “ per- instance “ object. High degree of customizability. Provides self-managing capabilities.

Goal 2. Adaptability Match the changing needs of the running applications. Contribute to the autonomic behavior of the system.

Goal 3. Extensibility / maintainability Support New hardware platforms or new applications easily. Updating components without interrupting the system.

Goal 4. Open-source compatibility Facilitates open-source collaboration. Supporting needs of specific user groups.

Design Principle Use modular object-oriented code(C++). Avoid centralized code paths, global data structure, and global locks. Move system functionality from the kernel to server processes and into application libraries. These principles should not conflicted with scalability / performance goal.

Structural overview of K42

All layers of K42 is based on object- oriented technology. Emulation layer Linux API and Linux ABI compatibility. Standard Linux system call are trapped and reflected to the K42 library.

Object-oriented design

Each resource is managed by a different set of object instances. Avoid global locks, global data structures, and global policies. Clustered object model makes the distinction between independent and dependent request trasnparent.

Achieve good performance on multiprocessors. No shared data structures and locks can be processed concurrently. Good locality of reference is achieved for resources accessed by a small number of processors. The clustered-object technology lets widely accessed objects be implemented in a distributed fashion.

Customizable Allows multiple policies and mechanisms to be supported simultaneously. Maintainable

User-mode implementation of system services Much of functionality is moved to libraries that is executed in the client process. Allows for a large degree of customization. Overhead is reduced. Thread scheduling, Timer interrupts, Page- fault handling, IPC services, I/O servers.

Additional K42 technologies Integrated performance monitoring Hot-swapping Customizable and scalable operation system KFS allows K42 to tailor the various workloads. Comprehensive scheduling Processors, I/O, memory, synchronization Lock avoidance Deletion of K42 objects is defferred.

Other K42 features K42 was Designed to run on 64-bit processors. K42 is fully preemptable. Most of kernel data structures are pageable.

Experiences Overall object-oriented design It might be difficult to achieve a desired global state. Trying to understand the interactions between the different components is complex. The more applications that increase, the more infrastructure of recording objects is needed.

Modularity for new applications and new HW A porting of K42 to the AMD**x86 64bit platform. Incorporating of test code for a new memory model into K42.

User-mode implementation This model is different from what an open- source Linux developer is used to. Version compatibility issues Multiple versions of the software that are themselves incompatible makes it difficult for K42 to support Linux.

Status and current directions HW PowerPC 64-bit platforms including POWER3*, POWER4+*, POWER MCA** G5 Apple G5 Xserve hardware. SW JVM SPEC(System Performance Evaluation Corporation) SDET(Software Development Envirenment Throughput) Apache MySQL

Conclusions K42 has the ability to serve as an open- source development platform. Its modularity structure makes it a valuable teaching, researching, and prototyping vehicle. Rapid prototyping of ideas.