What Is an Operating System III 2.1 Compnents II an Operating System
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Demystifying the Real-Time Linux Scheduling Latency
Demystifying the Real-Time Linux Scheduling Latency Daniel Bristot de Oliveira Red Hat, Italy [email protected] Daniel Casini Scuola Superiore Sant’Anna, Italy [email protected] Rômulo Silva de Oliveira Universidade Federal de Santa Catarina, Brazil [email protected] Tommaso Cucinotta Scuola Superiore Sant’Anna, Italy [email protected] Abstract Linux has become a viable operating system for many real-time workloads. However, the black-box approach adopted by cyclictest, the tool used to evaluate the main real-time metric of the kernel, the scheduling latency, along with the absence of a theoretically-sound description of the in-kernel behavior, sheds some doubts about Linux meriting the real-time adjective. Aiming at clarifying the PREEMPT_RT Linux scheduling latency, this paper leverages the Thread Synchronization Model of Linux to derive a set of properties and rules defining the Linux kernel behavior from a scheduling perspective. These rules are then leveraged to derive a sound bound to the scheduling latency, considering all the sources of delays occurring in all possible sequences of synchronization events in the kernel. This paper also presents a tracing method, efficient in time and memory overheads, to observe the kernel events needed to define the variables used in the analysis. This results in an easy-to-use tool for deriving reliable scheduling latency bounds that can be used in practice. Finally, an experimental analysis compares the cyclictest and the proposed tool, showing that the proposed method can find sound bounds faster with acceptable overheads. 2012 ACM Subject Classification Computer systems organization → Real-time operating systems Keywords and phrases Real-time operating systems, Linux kernel, PREEMPT_RT, Scheduling latency Digital Object Identifier 10.4230/LIPIcs.ECRTS.2020.9 Supplementary Material ECRTS 2020 Artifact Evaluation approved artifact available at https://doi.org/10.4230/DARTS.6.1.3. -
Context Switch in Linux – OS Course Memory Layout – General Picture
ContextContext switchswitch inin LinuxLinux ©Gabriel Kliot, Technion 1 Context switch in Linux – OS course Memory layout – general picture Stack Stack Stack Process X user memory Process Y user memory Process Z user memory Stack Stack Stack tss->esp0 TSS of CPU i task_struct task_struct task_struct Process X kernel Process Y kernel Process Z kernel stack stack and task_struct stack and task_struct and task_struct Kernel memory ©Gabriel Kliot, Technion 2 Context switch in Linux – OS course #1 – kernel stack after any system call, before context switch prev ss User Stack esp eflags cs … User Code eip TSS … orig_eax … tss->esp0 es Schedule() function frame esp ds eax Saved on the kernel stack during ebp a transition to task_struct kernel mode by a edi jump to interrupt and by SAVE_ALL esi macro edx thread.esp0 ecx ebx ©Gabriel Kliot, Technion 3 Context switch in Linux – OS course #2 – stack of prev before switch_to macro in schedule() func prev … Schedule() saved EAX, ECX, EDX Arguments to contex_switch() Return address to schedule() TSS Old (schedule’s()) EBP … tss->esp0 esp task_struct thread.eip thread.esp thread.esp0 ©Gabriel Kliot, Technion 4 Context switch in Linux – OS course #3 – switch_to: save esi, edi, ebp on the stack of prev prev … Schedule() saved EAX, ECX, EDX Arguments to contex_switch() Return address to schedule() TSS Old (schedule’s()) EBP … tss->esp0 ESI EDI EBP esp task_struct thread.eip thread.esp thread.esp0 ©Gabriel Kliot, Technion 5 Context switch in Linux – OS course #4 – switch_to: save esp in prev->thread.esp -
Overcoming Traditional Problems with OS Huge Page Management
MEGA: Overcoming Traditional Problems with OS Huge Page Management Theodore Michailidis Alex Delis Mema Roussopoulos University of Athens University of Athens University of Athens Athens, Greece Athens, Greece Athens, Greece [email protected] [email protected] [email protected] ABSTRACT KEYWORDS Modern computer systems now feature memory banks whose Huge pages, Address Translation, Memory Compaction aggregate size ranges from tens to hundreds of GBs. In this context, contemporary workloads can and do often consume ACM Reference Format: Theodore Michailidis, Alex Delis, and Mema Roussopoulos. 2019. vast amounts of main memory. This upsurge in memory con- MEGA: Overcoming Traditional Problems with OS Huge Page Man- sumption routinely results in increased virtual-to-physical agement. In The 12th ACM International Systems and Storage Con- address translations, and consequently and more importantly, ference (SYSTOR ’19), June 3–5, 2019, Haifa, Israel. ACM, New York, more translation misses. Both of these aspects collectively NY, USA, 11 pages. https://doi.org/10.1145/3319647.3325839 do hamper the performance of workload execution. A solu- tion aimed at dramatically reducing the number of address translation misses has been to provide hardware support for 1 INTRODUCTION pages with bigger sizes, termed huge pages. In this paper, we Computer memory capacities have been increasing sig- empirically demonstrate the benefits and drawbacks of using nificantly over the past decades, leading to the development such huge pages. In particular, we show that it is essential of memory hungry workloads that consume vast amounts for modern OS to refine their software mechanisms to more of main memory. This upsurge in memory consumption rou- effectively manage huge pages. -
Hang Analysis: Fighting Responsiveness Bugs
Hang Analysis: Fighting Responsiveness Bugs Xi Wang† Zhenyu Guo‡ Xuezheng Liu‡ Zhilei Xu† Haoxiang Lin‡ Xiaoge Wang† Zheng Zhang‡ †Tsinghua University ‡Microsoft Research Asia Abstract return to life. However, during the long wait, the user can neither Soft hang is an action that was expected to respond instantly but in- cancel the operation nor close the application. The user may have stead drives an application into a coma. While the application usu- to kill the application or even reboot the computer. ally responds eventually, users cannot issue other requests while The problem of “not responding” is widespread. In our expe- waiting. Such hang problems are widespread in productivity tools rience, hang has occurred in everyday productivity tools, such as such as desktop applications; similar issues arise in server programs office suites, web browsers and source control clients. The actions as well. Hang problems arise because the software contains block- that trigger the hang issues are often the ones that users expect to re- ing or time-consuming operations in graphical user interface (GUI) turn instantly, such as opening a file or connecting to a printer. As and other time-critical call paths that should not. shown in Figure 1(a), TortoiseSVN repository browser becomes unresponsive when a user clicks to expand a directory node of a This paper proposes HANGWIZ to find hang bugs in source code, which are difficult to eliminate before release by testing, remote source repository. The causes of “not responding” bugs may be complicated. An as they often depend on a user’s environment. HANGWIZ finds hang bugs by finding hang points: an invocation that is expected erroneous program that becomes unresponsive may contain dead- to complete quickly, such as a GUI action, but calls a blocking locks (Engler and Ashcraft 2003; Williams et al. -
Microkernel Mechanisms for Improving the Trustworthiness of Commodity Hardware
Microkernel Mechanisms for Improving the Trustworthiness of Commodity Hardware Yanyan Shen Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Computer Science and Engineering Faculty of Engineering March 2019 Thesis/Dissertation Sheet Surname/Family Name : Shen Given Name/s : Yanyan Abbreviation for degree as give in the University calendar : PhD Faculty : Faculty of Engineering School : School of Computer Science and Engineering Microkernel Mechanisms for Improving the Trustworthiness of Commodity Thesis Title : Hardware Abstract 350 words maximum: (PLEASE TYPE) The thesis presents microkernel-based software-implemented mechanisms for improving the trustworthiness of computer systems based on commercial off-the-shelf (COTS) hardware that can malfunction when the hardware is impacted by transient hardware faults. The hardware anomalies, if undetected, can cause data corruptions, system crashes, and security vulnerabilities, significantly undermining system dependability. Specifically, we adopt the single event upset (SEU) fault model and address transient CPU or memory faults. We take advantage of the functional correctness and isolation guarantee provided by the formally verified seL4 microkernel and hardware redundancy provided by multicore processors, design the redundant co-execution (RCoE) architecture that replicates a whole software system (including the microkernel) onto different CPU cores, and implement two variants, loosely-coupled redundant co-execution (LC-RCoE) and closely-coupled redundant co-execution (CC-RCoE), for the ARM and x86 architectures. RCoE treats each replica of the software system as a state machine and ensures that the replicas start from the same initial state, observe consistent inputs, perform equivalent state transitions, and thus produce consistent outputs during error-free executions. -
Asynchronous Page Faults Aix Did It Red Hat Author Gleb Natapov August 10, 2010
Asynchronous page faults Aix did it Red Hat Author Gleb Natapov August 10, 2010 Abstract Host memory overcommit may cause guest memory to be swapped. When guest vcpu access memory swapped out by a host its execution is suspended until memory is swapped back. Asynchronous page fault is a way to try and use guest vcpu more efficiently by allowing it to execute other tasks while page is brought back into memory. Part I How KVM Handles Guest Memory and What Inefficiency it Has With Regards to Host Swapping Mapping guest memory into host memory But we do it on demand Page fault happens on first guest access What happens on a page fault? 1 VMEXIT 2 kvm mmu page fault() 3 gfn to pfn() 4 get user pages fast() no previously mapped page and no swap entry found empty page is allocated 5 page is added into shadow/nested page table What happens on a page fault? 1 VMEXIT 2 kvm mmu page fault() 3 gfn to pfn() 4 get user pages fast() no previously mapped page and no swap entry found empty page is allocated 5 page is added into shadow/nested page table What happens on a page fault? 1 VMEXIT 2 kvm mmu page fault() 3 gfn to pfn() 4 get user pages fast() no previously mapped page and no swap entry found empty page is allocated 5 page is added into shadow/nested page table What happens on a page fault? 1 VMEXIT 2 kvm mmu page fault() 3 gfn to pfn() 4 get user pages fast() no previously mapped page and no swap entry found empty page is allocated 5 page is added into shadow/nested page table What happens on a page fault? 1 VMEXIT 2 kvm mmu page fault() 3 gfn to pfn() -
Advanced Operating Systems #1
<Slides download> https://www.pf.is.s.u-tokyo.ac.jp/classes Advanced Operating Systems #2 Hiroyuki Chishiro Project Lecturer Department of Computer Science Graduate School of Information Science and Technology The University of Tokyo Room 007 Introduction of Myself • Name: Hiroyuki Chishiro • Project Lecturer at Kato Laboratory in December 2017 - Present. • Short Bibliography • Ph.D. at Keio University on March 2012 (Yamasaki Laboratory: Same as Prof. Kato). • JSPS Research Fellow (PD) in April 2012 – March 2014. • Research Associate at Keio University in April 2014 – March 2016. • Assistant Professor at Advanced Institute of Industrial Technology in April 2016 – November 2017. • Research Interests • Real-Time Systems • Operating Systems • Middleware • Trading Systems Course Plan • Multi-core Resource Management • Many-core Resource Management • GPU Resource Management • Virtual Machines • Distributed File Systems • High-performance Networking • Memory Management • Network on a Chip • Embedded Real-time OS • Device Drivers • Linux Kernel Schedule 1. 2018.9.28 Introduction + Linux Kernel (Kato) 2. 2018.10.5 Linux Kernel (Chishiro) 3. 2018.10.12 Linux Kernel (Kato) 4. 2018.10.19 Linux Kernel (Kato) 5. 2018.10.26 Linux Kernel (Kato) 6. 2018.11.2 Advanced Research (Chishiro) 7. 2018.11.9 Advanced Research (Chishiro) 8. 2018.11.16 (No Class) 9. 2018.11.23 (Holiday) 10. 2018.11.30 Advanced Research (Kato) 11. 2018.12.7 Advanced Research (Kato) 12. 2018.12.14 Advanced Research (Chishiro) 13. 2018.12.21 Linux Kernel 14. 2019.1.11 Linux Kernel 15. 2019.1.18 (No Class) 16. 2019.1.25 (No Class) Linux Kernel Introducing Synchronization /* The cases for Linux */ Acknowledgement: Prof. -
Process Scheduling Ii
PROCESS SCHEDULING II CS124 – Operating Systems Spring 2021, Lecture 12 2 Real-Time Systems • Increasingly common to have systems with real-time scheduling requirements • Real-time systems are driven by specific events • Often a periodic hardware timer interrupt • Can also be other events, e.g. detecting a wheel slipping, or an optical sensor triggering, or a proximity sensor reaching a threshold • Event latency is the amount of time between an event occurring, and when it is actually serviced • Usually, real-time systems must keep event latency below a minimum required threshold • e.g. antilock braking system has 3-5 ms to respond to wheel-slide • The real-time system must try to meet its deadlines, regardless of system load • Of course, may not always be possible… 3 Real-Time Systems (2) • Hard real-time systems require tasks to be serviced before their deadlines, otherwise the system has failed • e.g. robotic assembly lines, antilock braking systems • Soft real-time systems do not guarantee tasks will be serviced before their deadlines • Typically only guarantee that real-time tasks will be higher priority than other non-real-time tasks • e.g. media players • Within the operating system, two latencies affect the event latency of the system’s response: • Interrupt latency is the time between an interrupt occurring, and the interrupt service routine beginning to execute • Dispatch latency is the time the scheduler dispatcher takes to switch from one process to another 4 Interrupt Latency • Interrupt latency in context: Interrupt! Task -
Integrating Preemption Threshold Scheduling and Dynamic Voltage Scaling for Energy Efficient Real-Time Systems
Integrating Preemption Threshold Scheduling and Dynamic Voltage Scaling for Energy Efficient Real-Time Systems Ravindra Jejurikar1 and Rajesh Gupta2 1 Centre for Embedded Computer Systems, University of California Irvine, Irvine CA 92697, USA jeÞÞ@cec׺ÙciºedÙ 2 Department of Computer Science and Engineering, University of California San Diego, La Jolla, CA 92093, USA gÙÔØa@c׺Ùc×dºedÙ Abstract. Preemption threshold scheduling (PTS) enables designing scalable real-time systems. PTS not only decreases the run-time overhead of the system, but can also be used to decrease the number of threads and the memory require- ments of the system. In this paper, we combine preemption threshold scheduling with dynamic voltage scaling to enable energy efficient scheduling in real-time systems. We consider scheduling with task priorities defined by the Earliest Dead- line First (EDF) policy. We present an algorithm to compute threshold preemption levels for tasks with given static slowdown factors. The proposed algorithm im- proves upon known algorithms in terms of time complexity. Experimental results show that preemption threshold scheduling reduces on an average 90% context switches, even in the presence of task slowdown. Further, we describe a dynamic slack reclamation technique that working in conjunction with PTS that yields on an average 10% additional energy savings. 1 Introduction With increasing mobility and proliferation of embedded systems, low power consump- tion is an important aspect of embedded systems design. Generally speaking, the pro- cessor consumes a significant portion of the total energy, primarily due to increased computational demands. Scaling the processor frequency and voltage based on the per- formance requirements can lead to considerable energy savings. -
Chapter 1. Origins of Mac OS X
1 Chapter 1. Origins of Mac OS X "Most ideas come from previous ideas." Alan Curtis Kay The Mac OS X operating system represents a rather successful coming together of paradigms, ideologies, and technologies that have often resisted each other in the past. A good example is the cordial relationship that exists between the command-line and graphical interfaces in Mac OS X. The system is a result of the trials and tribulations of Apple and NeXT, as well as their user and developer communities. Mac OS X exemplifies how a capable system can result from the direct or indirect efforts of corporations, academic and research communities, the Open Source and Free Software movements, and, of course, individuals. Apple has been around since 1976, and many accounts of its history have been told. If the story of Apple as a company is fascinating, so is the technical history of Apple's operating systems. In this chapter,[1] we will trace the history of Mac OS X, discussing several technologies whose confluence eventually led to the modern-day Apple operating system. [1] This book's accompanying web site (www.osxbook.com) provides a more detailed technical history of all of Apple's operating systems. 1 2 2 1 1.1. Apple's Quest for the[2] Operating System [2] Whereas the word "the" is used here to designate prominence and desirability, it is an interesting coincidence that "THE" was the name of a multiprogramming system described by Edsger W. Dijkstra in a 1968 paper. It was March 1988. The Macintosh had been around for four years. -
Mac OS X: an Introduction for Support Providers
Mac OS X: An Introduction for Support Providers Course Information Purpose of Course Mac OS X is the next-generation Macintosh operating system, utilizing a highly robust UNIX core with a brand new simplified user experience. It is the first successful attempt to provide a fully-functional graphical user experience in such an implementation without requiring the user to know or understand UNIX. This course is designed to provide a theoretical foundation for support providers seeking to provide user support for Mac OS X. It assumes the student has performed this role for Mac OS 9, and seeks to ground the student in Mac OS X using Mac OS 9 terms and concepts. Author: Robert Dorsett, manager, AppleCare Product Training & Readiness. Module Length: 2 hours Audience: Phone support, Apple Solutions Experts, Service Providers. Prerequisites: Experience supporting Mac OS 9 Course map: Operating Systems 101 Mac OS 9 and Cooperative Multitasking Mac OS X: Pre-emptive Multitasking and Protected Memory. Mac OS X: Symmetric Multiprocessing Components of Mac OS X The Layered Approach Darwin Core Services Graphics Services Application Environments Aqua Useful Mac OS X Jargon Bundles Frameworks Umbrella Frameworks Mac OS X Installation Initialization Options Installation Options Version 1.0 Copyright © 2001 by Apple Computer, Inc. All Rights Reserved. 1 Startup Keys Mac OS X Setup Assistant Mac OS 9 and Classic Standard Directory Names Quick Answers: Where do my __________ go? More Directory Names A Word on Paths Security UNIX and security Multiple user implementation Root Old Stuff in New Terms INITs in Mac OS X Fonts FKEYs Printing from Mac OS X Disk First Aid and Drive Setup Startup Items Mac OS 9 Control Panels and Functionality mapped to Mac OS X New Stuff to Check Out Review Questions Review Answers Further Reading Change history: 3/19/01: Removed comment about UFS volumes not being selectable by Startup Disk. -
Irmx® 286/Irmx® II Troubleshooting Guide
iRMX® 286/iRMX® II Troubleshooting Guide Q1/1990 Order Number: 273472-001 inter iRMX® 286/iRMX® II Troubleshooting Guide Q1/1990 Order Number: 273472-001 Intel Corporation 2402 W. Beardsley Road Phoenix, Arizona Mailstop DV2-42 Intel Corporation (UK) Ltd. Pipers Way Swindon, Wiltshire SN3 1 RJ United Kingdom Intel Japan KK 5-6 Tokodai, Toyosato-machi Tsukuba-gun Ibaragi-Pref. 300-26 An Intel Technical Report from Technical Support Operations Copyright ©1990, Intel Corporation Copyright ©1990, Intel Corporation The information in this document is subject to change without notice. Intel Corporation makes no warranty of any kind with regard to this material, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Intel Corporation assumes no responsibility for any errors that ~ay :!ppe3r in this d~ur:::ent. Intel Corpomtion make:; nc ccmmitmcut tv update nor to keep C"l..iiTeilt thc information contained in this document. Intel Corporation assUmes no responsibility for the use of any circuitry other than circuitry embodied in an Intel product. No other circuit patent licenses are implied. Intel software products are copyrighted by and shall remain the property of Intel Corporation. Use, duplication or disclosure is subject to restrictions stated in Intel's software license, or as defined in FAR 52.227-7013. No part of this document may be copied or reproduced in any form or by any means without the prior written consent of Intel Corporation. The following are trademarks of Intel Corporation