Program Loading and Memory Mapping in Linux

The goal here is to familiarize yourself with how programs are loaded, dynamically paged, and some of the mechanics of signal handling and memory mapping in Linux.

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Scheduler Activation

What is a thread? A thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler.

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Add MathJax v3 Support to Jekyll

I was using Mathjax v2 for a while and I heard v3 perform significantly better than v2. Many great tutorials explains explains how to add Mathjax support to Jekyll websites. Some of them only cover Mathjax v2. So here is the brief summary on how to add Mathjax v3 support to your Jekyll website.

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Linux Program Measurement and mmap

This is a summary over Linux kernel program measurement and mmap. The specs of our experiment environment is listed below. For more details regarding the CPU spec please refer to cpu world. This is the system spec:

Attribute Value
Processor name (BIOS) Intel(R) Core(TM) i7-6800K CPU @ 3.40GHz
Cores 6
Logical processors 12
TLB/Cache details 64-byte Prefetching Data TLB: 1-GB pages, 4-way set associative, 4 entries Data TLB: 4-KB Pages, 4-way set associative, 64 entries Instruction TLB: 4-KByte pages, 8-way set associative, 64 entries L2 TLB: 1-MB, 4-way set associative, 64-byte line size Shared 2nd-Level TLB: 4-KB / 2-MB pages, 6-way associative, 1536 entries. Plus, 1-GB pages, 4-way, 16 entries
RAM 32GB
Operating System Ubuntu 20.04.1 LTS
Kernel Version 5.4.0-47-generic


8-way set associative means the CPU cache is made up of sets that can fit 8 blocks each.

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Memory Resource Management in VMware ESX Server

VMWare ESX Server is a software layer designed to multiplex hardware resources among virtual machines running unmodified commodity operating systems. ESX Server, different to VMware Workstation, is a type 1 hypervisor, which means it runs directly on bare metal. ESX Server focuses on running guest VMs without modifying the guest OSes at all, which is challenging.

Memory Virtualization is done by interposing an extra abstraction layer between a physical address from the VM’s point of view, and a machine address which represents the actual hardware memory. ESX Server maintains a pmap data structure for each VM to translate PPMs to MPNs. A seperate shadow page table, consistent with the physical-to-machine mappings, is used to map virtual-to-machine page mappings. This avoids additional overheads as the hardware TLB will cache direct virtual-to-machine address translations read from the shadow page table.

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Xen and the Art of Virtualization

Xen is an x86 virtual machine monitor which allows multiple commodity operating systems to share conventional hardware in a safe and resource managed fashion, without sacrificing either performance or functionality. Xen is type I hypervisor, which directly runs on top of bare metal.

paravirtualization - presents a virtual machine abstraction that is similar but not identical to the underlying hardware.

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Start Linux Kernel Hacking

This is a summary of how to compile and boot the Linux kernel on the KVM-qemu virtual machine. It coveres how to get a VM running in KVM, how to build a customized kernel, and how to use GDB with the Linux kernel. The experiment is conducted on an amd64 architecture CPU. We use Ubuntu as our testing environment but the steps covered here should apply to other distros as well.

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Performance Anamoly of 802.11b

This research is conducted by Martin Heusse, Franck Rousseau, Cilles Berger-Sabbatel, Andrzej Duda on analyzing the performance of the IEEE 802.11b wireless local area networks. Degraded transmitting rate is caused by CSMA/CA channel access method.

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Exokernel

Exokernel is a term every system researcher has heard of at some point in life. However, according to the PDOS group at MIT, there aren’t any exokernel-baseed operating ssytems in active use today. It’s interesting to discover what ideas exokernels brought to the OS high-level design and some potential drawbacks of such design choice.

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Sketch on the UNIX Timesharing System

Unix is general-purpose, multi-user, interactive operating system, it offers several new features hardly found in other largers operating systems back in the day. These features include (1) a hierarchical file system incorporating demountable volumes; (2) compatible file, device, and inter-process I/O; (3) the ability to initiate asynchronous processes; (4) system command language selectable on a per-user basis; and (5) over 100 subsystems including a dozen languages.

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