Whats inside OS kernel

Arch Hooks in Linux Kernel

insidekernel — Wed, 22 Sep 2010 04:18:45 +0000

1. Interrupt Controller

2. dma_ops

3. Memory Management

4. System Bootup

5. Exception handling

6. Timer facilities

Linux Kernel Schedular

insidekernel — Tue, 14 Sep 2010 18:32:44 +0000

Every execution entity in Linux is a process with different priorities.
The processes either run in usermode, kernel mode, guest user mode, guest kernel mode
The processes are
1. user process
2. kernel process
3. work queue
4. softirq
5. tasklet
6. interrupt handler
  1. it does not have much of a process
7. user process running in kernel mode
The state of a process can be
1. running
2. preempted, waiting to run again
3. time slice completed
4. dying
5. waiting for a resource
Pre 2.6.23 Scheduler
1. user 2 run queues , active and expired
2. Each queue has 140 priority lists
3. the queues are per core, and a lock on each runQ protects it
4. In addition, with a runqueue per processor, a task generally shares affinity with a CPU and can better utilize the CPU’s hot cache.
5. the scheduler also offers dynamic task prioritization and SMP load balancing.
6. Every 200ms, a processor checks to see whether the CPU loads are unbalanced; if they are, the processor performs a cross-CPU balancing of tasks
Completely Fair Scheduler
1. Scheduling Entity
2. Scheduling Class
  1. Normal
  2. Real Time
  3. my own class

More to follow…

Hyper-Threading

insidekernel — Tue, 14 Sep 2010 18:31:21 +0000

From Understanding the linux kernel

A hyper-threaded chip is a microprocessor that executes several threads of execution at once; it includes several copies of the internal registers and quickly switches between them.

This technology allows the processor to exploit the machine cycles to execute another thread while the current thread is stalled for a memory access.

A hyper-threaded CPU is seen by Linux as several different logical CPU’s

Question: What does execute another thread above means ???

Linux Interrupt Framework

insidekernel — Tue, 07 Sep 2010 10:22:15 +0000

Lets disucss how linux interrupt framework works
(a) Client Driver
(b) Host Controller
(c) kernel interrupt routines.

Windows vs Linux Kernel

insidekernel — Sat, 24 Jul 2010 08:08:24 +0000

- Inserting a kernel Module
vs
- Adding a new service in Windows

Hypervisor Types

insidekernel — Sat, 24 Jul 2010 06:19:06 +0000

Types of hypervisors

Bare-Metal – Type 1

- Xen
-

Hosted – Type 2

-          Vmware
-          Sun Virtual box
-          Qemu
-          User Space Linux

Hybrid

- KVM ?

Cache Basics

insidekernel — Sat, 24 Jul 2010 06:06:11 +0000

- What is a cache
- Cache Line
- Addressing of caches
- Associativity
- Ways
- Example of a physically addressed cache operation
- Write Back / Write Through
- Non Cachable
- Cache Eviction
- Cache Flushing
- Snooping
- Multicore and Caches
- Cache Protocols

Virtualization Basics

insidekernel — Fri, 23 Jul 2010 07:49:39 +0000

What is virtualization?

Virtual + ization, from the name it means the process of making something virtual. The best example is Virtual Memory where the application is fooled by pretending the avalibility of a large memory area which in reality does not exist.
But the most common example of virtualization today is a virtual machine running under a hypervisor. Like Vmware, Xen, KVM, etc.

What is a hypervisor?

A hypervisor is a piece of software that manages virtual machines. The use is similar to a kernel to an user space application. This simple synonimity has great use cases

(a)    Application Virtualization
(b)   Desktop Virtualization
(c)    Platform Virtualization
(d)   IO Virtualization

JAVA Virtual Machine

Remember the popular Java virtual machine – which poplularized the platform independent stuff, well my take then was that its not platform independent at all. All it does is to put a JVM on that platform J
The Java program was running on top of JVM, which was translating it to the native calls. Java program didn’t assume anything about the system, and yes it was archtecture independent, it was running a byte code. So the JVM can exceute on any platform J

So lets extend this idea of having an x86 JVM like solution, but instead of byte code lets have a powerpc machine code. This is what today’s simulation solutions use eg windriver simics, / open sim. Let’s call it Cross Platfrom Virtualization.

QEMU

Google Dalvik VM

all of the 3 come into the category of

Application Virtualization

-          Legacy applications running on updated vs of OS with some incompatibilities
-          Ntvdm
-          Calls to file / registry apis are intercepted and redirected to a file.