Windows

Windows PRESENTED BY:

EZZAH BINT-E- SHAUKAT

TAYYABA ILYAS

M. SULEMAN TANVEER

THREADS: A thread is the entity within a

process that can be scheduled for execution. All threads of a process share its virtual address space and system resources. Each process is started with a single thread, but can create additional threads from any of its threads.

There are three basic components of Windows thread. All of these three components together create Windows thread:

Thread Kernel ObjectStackTEB Windows Thread

Components

What Windows Thread Consists Of

Thread Kernel Object

Operating systems use thread kernel objects for managing and executing threads across the system. Keeps all the statistical information about the thread.

Some of the important properties of thread kernel object are:

Thread ContextEach thread kernel object contains set of

CPU registers, called the thread's context. The context reflects state of the CPU registers when the thread last executed.

OS use kernel object context information while performing thread context switching.

Some of other important information held in thread kernel object about the thread.

StackUsed for maintaining local variables and functions.

Types of stackUser-mode stacko Used for local variables and arguments passed to methods.

Contains the address indicating what the thread should execute next.

o By default, Windows allocates 1 MB of memory for each thread’s user-mode stack

Kernel-mode stacko Used when application code passes arguments to a kernel function

in the operating system.o The kernel calls methods within itself and uses the kernel-mode

stack to pass its own arguments. o The kernel-mode stack is 12 KB when running on a 32-bit Windows

system and 24 KB when running on a 64-bit Windows system.

Thread Environment Block (TEB) TEB is a block of

memory allocated and initialized in user mode.

The TEB consumes 1 page of memory (4 KB on x86 and x64 CPUs).

 TEB contains information about exception handling which is used by SEH (Microsoft Structured Exception Handling).

Thread StateOperating system uses these states that are relevant to performance;

these are: Running - thread is using CPU Blocked - thread is waiting for input Ready - thread is ready to run (not Blocked or Running) Exited - thread has exited but not been destroyed

Thread State Diagram

Thread Scheduler Queues

Ready queueWaiting queues Exited queue: 

How OS runs Threads

Every 20 milliseconds or so, OS thread scheduler looks at all the thread kernel objects currently inside Ready Queue.

Introduction to windows osMicrosoft Windows came to dominate the

world's personal computer market.

The most recent version of Windows is Windows

8.

Windows uses demand paging with Clustering.

Clustering handles page faults by bringing in

not only the faulting page but also the multiple

pages surrounding the faulting page.

Windows uses clock algorithm.

What is Virtual Memory?Memory that appears to exits as Main Memory.

CPU can address up to 3GB of memory, using its full

32 bits.

The hardware provides for programs to operate in

terms of as much as they wish of this full 4GB space

as Virtual Memory, those parts of the program and

data which are currently active being loaded into

Physical Random Access Memory (RAM).

Why virtual memory?The first is to allow the use of programs

that are too big to physically fit in the

memory.

The other reason is to allow for

multitasking – multiple programs running

at once. 

Virtual Memory in WindowsIn Windows the processor manages the mapping in

terms of pages.

Page size of 4 KB each.

Only some parts of the program and data that are

currently in active needs to be held in physical

RAM.

Other parts are then held in a swap file or page

file.

Address space of Windows32-bit Address Space

32-bits = 2^32 = 4 GB

3 GB for address space

1 GB for kernel mode

64-bit Address space

64-bits = 2^64 = 17,179,869,184 GB

x64 today supports 48 bits virtual = 262,144 GB = 256 TB

IA-64 today support 50 bits virtual = 1,048,576 GB = 1024 TB

64-bit Windows supports 44 bits = 16,384 GB = 16 TB

Virtual Address Space (V.A.S.)

Process space contains:

The application you are running (.EXE + .DLLs (dynamic link library ))

A user-mode stack for each thread

UserAccessible

Kernel-modeaccessible

00000000

7FFFFFFF

80000000

Unique perprocess

System-wide

Virtual Address Space (V.A.S.)

System space contains:Executive, Kernel Statically-allocated

system-wide data cellsPage tablesKernel-mode device

driversFile system cacheA kernel-mode stack

for every thread in every process

UserAccessible

Kernel-modeaccessible

00000000

7FFFFFFF

80000000

FFFFFFFF

Unique perprocess

System-wide

Virtual Address TranslationHardware converts each valid virtual address to a physical address

Address translation (hardware)

Virtual page number Byte within page

Byte within pagePhysical page number

PageTables

TranslationLookaside

Buffer

PageDirectory

virtual address

physical address

If page not valid

Page fault

.

Virtual Address Translation

What is loaded in RAM?

Items of RAM can be divided into two parts :

-Non paged area

Parts of system which are very important . This cannot

be paged out.

-page pool

Program code, Data pages that had actual data written

to them.

Disadvantages of virtual memory

Virtual memory can slow down performance.

If the size of virtual memory is quite large in comparison to

the real memory, then more swapping to and from the hard

disk will occur as a result.

Accessing the hard disk is far slower than using system

memory.

Using too many programs at once in a system with an

insufficient amount of RAM results in constant disk

swapping – also called thrashing.

Page faults

When the program needs the page which is not in

main memory the page fault interrupt will be invoked.

If this is available on disk then it will be swapped.

If it is not available due to some hardware problems

the system will have ‘invalid page fault error’.

It may manifest itself as a ‘blue screen’ failure with a

STOP code.

Page FaultsA page fault occurs when there is a reference to a page

that isn’t mapped to a physical page

The system goes to the appropriate block in the associated

file to find the contents of the page:

Physical page is allocated

Block is read into physical page

Page table entry is filled in

Exception is dismissed

Processor re-executes the instruction that caused the

page fault

The page has now been “faulted into” the process

“working set”

Pages are only brought into memory as a result of page

faults

Working Set Each process has a default working set minimum and

maximum

Can change with SetProcessWorkingSet

Working set minimum controls maximum number of

locked pages (Virtual Lock)

Minimum is also reserved from RAM as a guarantee

to the process

Working set maximum is ignored

If there’s ample memory, process working set represents

all the memory it has referenced (but not freed)

Working Set List

All the physical pages “owned” by a process

E.g. the pages the process can reference without

incurring a page fault

A process always starts with an empty working set

It then incurs page faults when referencing a page that

isn’t in its working set

Working Set

newer pages older pages

Working Set Replacement

When memory manager decides the process is large

enough, it give up pages to make room for new pages

Local page replacement policy

o Means that a single process cannot take over all of

physical memory unless other processes aren’t using it

o Page replacement algorithm is least recently accessed

(pages are aged when available memory is low)

Working Set

To standby or modified

page list

Working Set BreakdownConsists of 2 types of pages:

Shareable (of which some may be shared)

Private

Four performance counters available:

Working Set Shareable

o Working Set Shared (subset of shareable that are

currently shared)

Working Set Private

Working Set Size (total of WS Shareable+Private)

o Note: adding this up for each process over counts shared

pages

Standby and Modified Page ListsModified pages go to modified (dirty) list

Avoids writing pages back to disk too soon

Unmodified pages go to standby (clean) lists

They form a system-wide cache of “pages likely to be needed

again”

Pages can be faulted back into a process from the

standby and modified page list

These are counted as page faults, but not page reads

Modified Page Writer

When modified list reaches certain size, modified page

writer system thread is awoken to write pages out

o Also triggered when memory is overcommitted (too few

free pages)

o Does not flush entire modified page list

Pages move from the modified list to the standby list

o E.g. can still be soft faulted into a working set

Thank you