Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles (SOSP), pages 237--250, Copper Mountain, CO, USA, December 1995.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....The kernel only provides a mechanism for memory management; the actual policy is implemented by user level applications. In the following sections, we discuss each of these approaches in more detail, and we describe and cite related work. 2.1. 1 Static in kernel policy The L4 microkernel [34] allocates metadata from an in kernel memory pool, which is created during startup and has a fixed size. As long as there is enough free space available, new requests are always granted. When the pool is exhausted, no new metadata can be allocated, and the respective system call fails with an ....

....from customizing this policy as well, e.g. by evicting less important objects first. The resulting problem is similar to the one discussed in this thesis. 2.1. 4 User level managers Liedtke et al. 36] proposed an extension to the memory pool model that was used in the original L4 microkernel [34]. In their approach, the kernel still allocates metadata from an in kernel memory pool and fails system calls when this pool is exhausted. However, applications can resolve this situation by donating some of their own memory to the kernel. User level memory managers must ensure that the memory ....

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Jochen Liedtke. On -kernel construction. In Proceedings of the fifteenth ACM Symposium on Operating systems principles. ACM Press, Dec 1995.

....with. Examples include the wireless communication, which was to be implemented via Sunswift s RangeLAN 2 access points from Proxim. These require an Ethernet interface. The PLEB is a StrongARM SA1100 based computer. Both ARM Linux, and research operating systems based on the L4 micro kernel [27] have been successfully booted and used in applications on this platform. The StrongARM processor runs at 200Mhz, and can have up to 64MB RAM, 8MB flash. A number of internal peripherals are available. The PLEB s stacking daughtercard arrangement (similar to that used for the CANRefNodes) is used ....

Jochen Liedtke. On -kernel construction. In sosp95, pages 237--250, Copper Mountain, CO, USA, December 1995.

....17 5 Benchmarks 17 6 Future Work and Discussion 18 3 4 1 Introduction This document describes the mechanisms used within the L4 Alpha microkernel to extend the L4 API to systems with multiple processors. Basic knowledge of the L4 microkernel is assumed; for a more general discussion of L4, see [Lie95,Lie96], as well as the user manual [AH98] Basic knowledge of the Alpha family of microprocessors is also assumed; see [Com98] for more information. For an introduction to L4 Alpha see the L4 Alpha reference manual [PWH01] 1.1 Goals The development of this microkernel was done with the following ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles (SOSP), pages 237--250, Copper Mountain, CO, USA, December 1995.

....to the scheduling mechanisms exported by L4 itself. 1.2 Goals The aim of this thesis is to design, implement, and evaluate a secure, exible, and high performance scheduler for the L4 kernel. Security The main design goal of L4 is a minimalist kernel with respect to security, as espoused in [Lie95] Thus, security should be the major concern of any scheduling mechanisms implemented by L4. Flexibility As L4 is a microkernel, it must support a wide range of di erent OS personalities, sometimes concurrently. This means that any mechanism must allow di erent, competing scheduling policies at ....

....alternative, ticks, is also desirable in that it is central to the granularity of services provided by the system, especially timeslice length and minimum timeouts. In deciding between the two for the scheduler implementation in L4, the philosophy of L4 needs to be taken into consideration. In [Lie95] an ecient kernel is shown to be inherently non portable, as portability requires a tradeo with performance. Also, a feature is included in the kernel only if exporting it to user space would constitute a security aw. The granularity of scheduling should be exported to the systems built on ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237-250, Copper Mountain, CO, USA, December 1995.

.... purpose time sharing systems to be implemented on top of it, with the option for concurrently running other operating system personalities [HHW98] The biggest concern in using a microkernel base was the poor performance displayed by rst generation microkernels [CB93, Lie96d] The L4 microkernel [Lie95b, Lie96a, AH98] presented itself as an ideal choice not only due to its high performance implementations, but since the research group behind the PLEB project have a solid experience base with L4. This experience is due to the usage of L4 MIPS [EHL97] in teaching and research [HEV 98] at the ....

....in this thesis, most unique to the ARM and or SA 1100, as well others more general to the targeted application areas. The general philosophy of L4 can be regarded as minimalist. In minimising the size and complexity of the microkernel, its interference with user programs is minimised [Lie96b, Lie95b] In light of this, the overall constraint on the design and implementation should be to minimise all data structures and code in terms of their size and complexity. 3.1 Exception Handling L4 makes use of IPC to communicate all events to user space handlers. The majority of exceptions raised in ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237-250, Copper Mountain, CO, USA, December 1995.

....based completely on informational requests. Separating the privileges of an application causes a decomposition into subsystems with well de ned functionality. This is similar to the design and functionality of a kernel where subsystems have to follow the principle of independence and integrity [10]. For a privilege separated application, independence and integrity are realized by multiple processes that have separate address spaces and communicate via IPC. 8 Conclusion Programming errors in privileged services can result in system compromise allowing an attacker to gain unauthorized ....

Jochen Liedtke. On -Kernel Construction. In Proceedings of the Symposium on Operating Systems Principles, pages 237-250, 1995.

....malfunction in a service is isolated like a malfunction to a user program. Finally, a micro kernel system is more exible and tailor able: di erent implementations of the same service can easily co exist. A micro kernel design is far superior to a monolithic kernel in terms of software engineering [12, 13]. However, most micro kernels su er from poor performance, which has prevented their wide spread adoption. The exported procedure call (EPC) provides many of the above advantages without forcing the adoption of an entirely new operating system. There is some overhead to exporting an operation. ....

Jochen Liedtke. On -kernel construction. In Proc. Fifteenth ACM Symp. on Operating Systems Principles, pages 237-250, Copper Mountain Resort, CO, December 1995.

....system functions are implemented by user level servers. The aim of microkernels is modularity and thus robustness and exibility. As shown in Figure 10 applications use the services provided by the kernel and shared servers. Beyond the mechanisms that have to be supported by the kernel, Liedtke [36] mentions address spaces, threads and IPC as well as unique identi ers that are required for reliable local communication. Due to lack of performance (communicating with a shared server is performed via the kernel and thus includes two context switches) some microkernels have re integrated servers ....

Jochen Liedtke. On -kernel construction. In ACM Symposium on Operating Systems Principle (SOSP), pages 237-250, Copper Mountain Resort, December 1995.

....that are associated with a full blown mobile agent system. Hence, TOS supplies only the minimal amount of function needed to support its extension to the functions that are actually required. In this sense, we have borrowed from the work on extensibility in operating system kernels (e.g. [18, 4, 6, 21]) by including in TOS only the mechanisms needed to securely implement di erent mobility functions. Doing so helps TOS meet the third requirement listed above. For example, we have found it rare for a DiSM policy to require an itinerant agent that is, an agent that can move from machine to ....

Jochen Liedtke. On -Kernel Construction. In Proceedings of the 15th Symposium on Operating System Principles, pages 237-250, Copper Mountain, Colorado, Dec 1995.

....a blocking RPC call, which spawns a new thread in t p for the duration of the PDX execution. The operation of creating a new thread and transferring control to it is very lightweight in Mungi, as it maps directly onto the corresponding operations of the underlying, very efficient, L4 microkernel [Lie95] In the case of a proper protection domain extension (i.e. a null clist parameter is passed) t p can inherit t s cached validations by having t p reference t s segment list. If, during p s execution, new objects are validated, these validations are prepended to t p s segment list, without ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237--250, Copper Mountain, CO, USA, December 1995.

....path of the most frequently used operations. However, performance of these first generation microkernels proved disappointing, with applications generally experiencing a significant slowdown compared to a traditional ( monolithic ) operating system [CB93] Liedtke, however, has shown [Lie93, Lie95, Lie96] that these performance problems are not inherent in the microkernel concept and can be overcome by good design and implementation. L4 is the constructive proof of this theorem, as has been clearly demonstrated by Hartig et al. HHL 97] 1.1 L4 design philosophy The most fundamental ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237--250, Copper Mountain, CO, USA, December 1995.

....of operating systems by dividing systems into smaller units or components. However, early systems like Chorus [10] or Mach [4] su ered from poor inter process communication (IPC) performance. This resulted in the common opinion that microkernel based system are inherently slow. Recent work [7, 6] has shown that modern microkernel architecture can improve IPC performance signi cantly and that microkernel based systems can approach the performance of traditional monolithic systems. However, there is another problem such systems have to attack: usability. The microkernel provides general ....

Jochen Liedtke. On -Kernel Construction. In Proceedings of the 15th ACM Symposium on Operating System Principles (SOSP), 1995.

....have been investigated in order to achieve this goal. ffl User level: This approach adds services at user level, making sure that the kernel provides the mechanisms to be able to enforce some level of protection. Examples include Cache Kernel [CD94] Exokernel [EKO95] Pilot [RDH 80] L4 L3 [Lie95] ffl Kernel level: Adding services to the kernel in a safe and secure way. Examples include SPIN s kernel loadable modules [BSP 95] and software fault isolation techniques [WLAG93, SESS96] The next sections will examine these approaches in more detail. 5.2.1 Exokernel The Exokernel ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237--250, Copper Mountain, CO, USA, December 1995.

....to a remote node for execution is a form of ordinary remote evaluation [14] with our mobile code plane being responsible for its configuration. For work on handling software mobility at the level of native code only, we may also refer to [9] Beside general and older work on micro and nanokernels [7,10,4], Mach [1] Chorus [12] process migration [2] and Exokernel [6] we point to a paper that is closely related to our work and was published in 1985: in [3] Banino et al. describe activity messages which are a special form of messages sent between Chorus actors . They can influence how the ....

Jochen Liedtke. On -Kernel Construction. In Proceedings of the Fifteenth ACM Symposium on Operating Systems Principles, volume 29 of ACM Operating Systems Review, pages 237--250, December 1995.

....to relatively small dedicated real time systems. Maturity of the system can only be achieved by using it on a daily basis. DROPS provides full binary compatibility to the standard Linux ABI, making all Linux applications automatically available for use on our platform. Based on the L4 kernel [19], DROPS incorporates multiple OS personalities: Standard time sharing tasks use the L4Linux server, a port of the monolithic Linux kernel to the L4 kernel [15] Real time applications are free to use dedicated real time servers for predictable performance. Drivers (e.g. the ATM NIC driver) run ....

Jochen Liedtke. On -Kernel Construction. In ACM Symposium On Operating System Principles, 1995.

....cost of cleaning (writing back) the data cache is particularly expensive since each line must be individually cleaned. The purpose of this paper is to present an approach to providing fast address space switches on the StrongARM, and discuss its proposed implementation in the L4 microkernel [Lie95b, Lie96, AH98] 2 StrongARM Virtual Memory Architecture In this section we summarise the StrongARM s virtual memory architecture as far as relevant to the topic of this paper. We describe general ARM features and note which features are speci c to the StrongARM. 2.1 ARM page table structure The ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237-250, Copper Mountain, CO, USA, December 1995.

....performance out of such systems, it is important to use page tables which support efficiently the operations these kernels require. In this paper we examine these issues in detail. We use a representative architecture, the MIPS R4x00 family [6] and our own implementation of the L4 microkernel [7,8] as a testbed. L4 is presently the fastest kernel available [9] its low intrinsic overhead makes it particularly sensitive to page table performance, and therefore an ideal target for such an investigation. The goal of this study is to examine how various page table structures perform under ....

....switching overhead. 3 Methodology In order to investigate the performance implications of these page table structures, we have performed a number of experiments, running a set of benchmarks on an instrumented kernel. 3. 1 Test bed As mentioned earlier, we use for our experiments the L4 kernel [7, 8] running on a 100MHz MIPS R4700 processor [6] The R4700 has a tagged, software loaded TLB with 48 entries, each entry mapping a pair of contiguous virtual pages of 4kb each. The processor supports a 40 bit address space. However, we designed our page tables to work with full 64 bit addresses. L4 ....

Jochen Liedtke. On ¯-kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237--250, Copper Mountain, CO, USA, December 1995.

....the checkpointing design (Sects. 4, 5, and 6) we give a brief overview of the kernel used as a base for the implementation (Sect. 2) and our general approach (Sect. 3) Section 7 lists related work, and nally Sect. 8 concludes. 2 Implementation Basis: The L4 Kernel The L4 kernel [10] is a lean second generation kernel. The philosophy behind the kernel is that only a minimal set of concepts is implemented within it. A concept is permitted inside the kernel only if moving it outside the kernel would prevent some system functionality to be implemented. In other words, the ....

....Recursive Address Spaces Recursive address spaces forms a concept that is relied heavily upon by the checkpointing facility presented in this paper. With recursive address spaces, 1 A rationale for the choice of these basic abstractions and a detailed description of the L4 kernel is given in [10]. L4 kernel Faulting Thread Handler Thread 1 2 3 Fig. 1. Page fault IPC. When a page fault occurs in a user level thread; 1) a page fault exception is raised and caught by the kernel, 2) the kernel generates a page fault IPC from the faulting thread to the handler thread, and (3) the ....

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Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on Operating System Principles (SOSP '95), Copper Mountain Resort, CO, December 3-6 1995.

....an Unmap operation. ABC PM: VM: ABC ABC from to ABC PM: ABC VM: from to Figure 3: Address space before (left) and after (right) execution of an Unmap(from,length) system call. Crossed out pages are unmapped. 2. 5 Recursive address spaces Systems like Grasshopper [DdB 94] and L4 [Lie95] use similar mapping operations, but use them in a hierarchical fashion to recursively construct address spaces. This does not fit the SASOS model, as there can only be one address space, so mappings can only operate between different parts of the same address space. However, pagers can be nested ....

Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237--250, Copper Mountain, CO, USA, December 1995.

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Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles (SOSP), pages 237--250, Copper Mountain, CO, USA, December 1995.

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Jochen Liedtke. On -kernel construction. In Proceedings of the 15th ACM Symposium on OS Principles, pages 237--250, Copper Mountain, CO, USA, December 1995. 90

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Jochen Liedtke. On -kernel construction. In Proc. 15th ACM SOSP, pages 237--

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Jochen Liedtke. On -kernel construction. In Proc. 15th ACM SOSP, pages 237--

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