IRIX is the Bestix: An Overview of the IRIX Operating System

CS 351 – Operating SystemsSpring 2001Section 002

GROUP B:Matthew BoyerChristian DunlapSteven HughesPatrick QuentmeyerShelley SloaneMichael Williams

Overview of IRIX

• Developed in 1982 by SGI

• First Unix OS to support symmetric multi-

processing

• first UNIX OS to support 64 and 32 bit

environments

• First Unix OS to support advanced realtime and

graphics features

IRIX History

Overview of IRIX

• Designed for high performance computing,

advanced graphics and visual computing platforms

• Rich set of scalability, big data management, and

real-time 3D visualization enhancements

• Compliant with UNIX SVR4 and The Open Group's

standards including UNIX 95, Year 2000, and

POSIX.

IRIX 6.5

Overview of IRIX

• Used mainly by Researchers and Graphic designers

• IRIX is used to:

– “Carry out grand initiatives in fundamental and advanced research to improve

health, save lives, …”

– “Extend our ability to create and use new kinds of supercomputing capabilities,

build safer and more efficient cars and aircraft, contribute to national security…”

– “There are researchers that do important work with IRIX because, in some

cases, nothing else can do the job.”

-John Mashey, SGI chief

scientist

IRIX 6.5 (cont.)

Overview of IRIX

1. Must be all platforms: no special, platform-

specific IRIX releases.

2. Releases will adhere to a predictable schedule.

3. Must be 100% reliable.

4. Must maintain application binary compatibility.

5. Must always perform at the highest possible level.

Primary Goals

Process States in IRIX

Process scheduling is non-premptive.

Process can yield to another process through an I/O request.

Process time limits enforced by kernel using time slicing.

Process information can be found using the ps command.

Process States in IRIX

Process States in IRIX

Process state information can be found from the ps command using the option -S

Return Value IRIX State Stallings State

O Process is running on the processor Running

S Process is sleeping, waiting for resource. Blocked

R Process is running Running

Z Process is terminated and parent not waiting Exit

T Process is stopped Ready

I Process is in intermediate state of creation New

X Process is waiting for memory Blocked

Z Process is creating core image after error Running Ready

Process States (cont.)

Memory Management in IRIX

• Memory management extremely important because of multiprocessor environment.

• Must produce reasonable levels of locality via page migration and replication in multiple processes.

• IRIX allows for each application to control how memory is allocated and managed.

• This is to minimize access and write times.

IRIX Memory Management

Memory Management in IRIX

• Attached to each process there is a Policy Module.• The Policy Module holds variables that determine

the behaviors for:– Initial Allocation (placement, page size and

fallback policies)– Dynamic Relocation (migration and replication

policies)– Paging (paging policy)

Application Controlled Memory Management

Memory Management in IRIX

• First, Placement Policy is called, returns a handle identifying a node where the page should be placed.

• Page Size Policy determines the page size according to properties of process.

• If not enough space is available on current node the Fallback Policy is called to chose a different node, smaller page size, sleep or fail.

• Fallback policy is determined by the kinds of memory access pattern on application exhibits.

Memory Allocation

Memory Management in IRIX

• Once a page is allocated, it stays on it’s node until it needs to be migrated, paged out, or faulted back in.

• Migration controlled by Migration Policy. Migration is necessary in cases where certain pages are called more and must be moved to improve access time.

• Replication controlled by Replication Policy. Read-only text can be replicated for use by multiple processes running on different nodes.

Memory Allocation (cont.)

Threads in IRIX

• IRIX uses POSIX-style threads or pthreads.• Initially there is one thread for one process, but

programmers can split processes into multiple threads which my run in the same address space.

• Attributes of threads can be changed by calling methods with certain arguments.

• Some of these attributes are scheduling scope, stack size, address for stack, and starting thread priority.

Threads

Threads in IRIX

• In IRIX, processes can use either threads or a scaled down version of a process called a lightweight process.– Less portable and create higher overhead– Can have its own file descriptors– Do not allow for modification of data that is

shared with other lightweight processes, while threads do.

Threads vs. Lightweight Processes

Mutual Exclusion in IRIX

• Mutual Exclusion provides exclusive rights to system resources

• IRIX has several constructs for handling mutual exclusion

• Implementation methods depend on need and system architecture

• Special Mutual Exclusion Methods

Mutual Exclusion

Mutual Exclusion in IRIX

• Test and Set – hardware features

• Locks – access the Test and Set in hardware using Locks

• Semaphores – controlled structures

• Polled – many resources from semaphores on a poll

• Unpolled – one semaphore structure per resource

• Barriers – enforces proper parallel processing

Methods

File Management through filesystems in IRIX

A Filesystem is a data structure that organizes files and directories on a diskpartition for easy retrieval when needed.

Overview

A File is a one-dimensional array of bytes with no other structure implied.

A Directory is a container that stores files and other directories.

The combination of directories and files make up a filesystem.

File Management through filesystems in IRIX

Information about each file is stored in a structure called an inode.

An inode is a data structure that stores all information about file except its name.

Each inode has an identifying inode number, which is unique across the filesystem.

An inode contains:- type of the file- access mode of the file (read, write, and execute)- number of hard links to the file- owner’s user-ID number and group-ID number- size of the file in bytes- date and time the file was last accessed and modified- information for finding the file’s data within the disk parition or logical volume- pathname of symbolic links

Inodes

File Management through filesystems in IRIX

Hard Links

Information about each file is stored in an inode for the file. The name of thefile is stored in the file’s directory and associating the filename with an inodenumber creates a link to the file. This kind of link is called a hard link.

Consider a current directory contains: a file called ‘origfile’ and a hard link called‘linkfile’ connected to ‘origfile’. Since ‘origfile’ and ‘linkfile’ are now two names forthe same file, changes in the file’s content are visible when using either filename.If one of the links is removed there will no be effect on the other link.

Symbolic Links

The symbolic link is really just a file. This file contains the pathname ofanother file or directory as a text string. The symbolic link can point to a fileor directory in another filesystem.

The symbolic link can become useless if the file or directory it points to is removed. When this happens to the target of the symbolic link, the linkbecomes known as a dangling symbolic link.

Hard Links and Symbolic Links

File Management through filesystems in IRIX

Filesystems do not have actual names. Instead, they are identified by locationon a disk or the position in the directory structure.

The filesystems can be located and identified with the following information:

- The block and character device file names of the disk partition or logical volume that holds the specific filesystems.- A mnemonic name for the disk partition or logical volume that holds the filesystem.- The mount point for the filesystem.

Filesystem Names

File Management through filesystems in IRIX

XFS Filesystem is one type of filesystem specially created for Silicon Graphics Inc.

Some of XFS’s important features:- Full 64-bit file capabilities- Efficient support of large, sparse files (files containing ‘holes’)- Rapid and reliable recovery after crashes because of journaling technology- Integrated, full-function volume manager, known as XLV Volume Manager- Very high I/O performance that scales well on multiprocessing systems

XFS is designed to be a very high performance filesystem. Under certain conditions,throughput exceeds 100 MB per second. The performance of the XFS filesystem isscaled to complement the Challenge MP architecture and the Origin 2000 architecture.While traditional filesystems suffer from reduced performance as they grow in size,the XFS filesystem has no performance penalty.

XFS Filesystems

Thank you.