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Dave Probert, Ph.D. - Windows Kernel Architect Microsoft Windows Division Evolution of the Windows Kernel Architecture 08.10.2009 Buenos Aires About Me Ph.D. in Computer Engineering (Operating Systems w/o Kernels) Kernel Architect at Microsoft for over 13 years

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dave probert ph d windows kernel architect microsoft windows division
Dave Probert, Ph.D. - Windows Kernel Architect

Microsoft Windows Division

Evolution of the Windows Kernel Architecture

08.10.2009

Buenos Aires

Copyright Microsoft Corporation

about me
About Me
  • Ph.D. in Computer Engineering (Operating Systems w/o Kernels)
  • Kernel Architect at Microsoft for over 13 years
    • Managed platform-independent kernel development in Win2K/XP
    • Working on multi-core & heterogeneous parallel computing support
      • Architect for UMS in Windows 7 / Windows Server 2008 R2
  • Co-instigator of the Windows Academic Program
    • Providing kernel source and curriculum materials to universities
    • http://microsoft.com/WindowsAcademic or compsci@microsoft.com
    • Wrote the Windows material for leading OS textbooks
      • Tanenbaum, Silberschatz, Stallings
      • Consulted on others, including a successful OS textbook in China
unix vs nt design environments
UNIX vs NT Design Environments

Copyright Microsoft Corporation

effect on os design
Effect on OS Design

Copyright Microsoft Corporation

today s environment 2009
Today’s Environment [2009]

Copyright Microsoft Corporation

windows architecture

ServiceControl Mgr.

LSASS

SvcHost.Exe

Task Manager

WinMgt.Exe

Explorer

WinLogon

SpoolSv.Exe

User

Application

Services.Exe

User

Mode

Subsystem DLLs

Kernel

Mode

Windows Architecture

Environment Subsystems

System Processes

Services

Applications

Windows

OS/2

Session Manager

POSIX

Windows DLLs

System

Threads

NTDLL.DLL

System Service Dispatcher

(kernel mode callable interfaces)

Windows

USER,

GDI

I/O Mgr

File System Cache

Object

Mgr.

Plug and

Play Mgr.

Power

Mgr.

SecurityReferenceMonitor

VirtualMemory

Processes&

Threads

Configura-

tion Mgr

(registry)

Local

Procedure

Call

Device &

File Sys.

Drivers

Graphics

Drivers

Kernel

Hardware Abstraction Layer (HAL)

hardware interfaces (buses, I/O devices, interrupts, interval timers, DMA, memory cache control, etc., etc.)

Copyright Microsoft Corporation

kernel mode architecture of windows
Kernel-mode Architecture of Windows

user mode

NT API stubs (wrap sysenter) -- system library (ntdll.dll)

NTOS kernel layer

Trap/Exception/Interrupt Dispatch

CPU mgmt: scheduling, synchr, ISRs/DPCs/APCs

Drivers

Devices, Filters, Volumes, Networking, Graphics

Procs/Threads

IPC

Object Mgr

kernel mode

Virtual Memory

glue

Security

Caching Mgr

I/O

Registry

NTOS executive layer

Hardware Abstraction Layer (HAL): BIOS/chipset details

firmware/ hardware

CPU, MMU, APIC, BIOS/ACPI, memory, devices

Copyright Microsoft Corporation

Copyright Microsoft Corporation

kernel executive layers
Kernel/Executive layers
  • Kernel layer – ntos/ke – ~ 5% of NTOS source)
    • Abstracts the CPU
      • Threads, Asynchronous Procedure Calls (APCs)
      • Interrupt Service Routines (ISRs)
      • Deferred Procedure Calls (DPCs – aka Software Interrupts)
    • Providers low-level synchronization
  • Executive layer
    • OS Services running in a multithreaded environment
    • Full virtual memory, heap, handles
    • Extensions to NTOS: drivers, file systems, network, …

Copyright Microsoft Corporation

nt native api examples
NT (Native) API examples

NtCreateProcess(&ProcHandle, Access, SectionHandle, DebugPort, ExceptionPort, …)

NtCreateThread(&ThreadHandle, ProcHandle, Access, ThreadContext, bCreateSuspended, …)

NtAllocateVirtualMemory(ProcHandle, Addr, Size, Type, Protection, …)

NtMapViewOfSection(SectionHandle, ProcHandle, Addr, Size, Protection, …)

NtReadVirtualMemory(ProcHandle, Addr, Size, …)

NtDuplicateObject(srcProcHandle, srcObjHandle, dstProcHandle, dstHandle, Access, Attributes, Options)

Copyright Microsoft Corporation

windows vista kernel changes
Windows Vista Kernel Changes
  • Kernel changes mostly minor improvements
    • Algorithms, scalability, code maintainability
    • CPU timing: Uses Time Stamp Counter (TSC)
      • Interrupts not charged to threads
      • Timing and quanta are more accurate
    • Communication
      • ALPC: Advanced Lightweight Procedure Calls
      • Kernel-mode RPC
      • New TCP/IP stack (integrated IPv4 and IPv6)
    • I/O
      • Remove a context switch from I/O Completion Ports
      • I/O cancellation improvements
    • Memory management
      • Address space randomization (DLLs, stacks)
      • Kernel address space dynamically configured
    • Security: BitLocker, DRM, UAC, Integrity Levels

Copyright Microsoft Corporation

windows 7 kernel changes
Windows 7 Kernel Changes
  • Miscellaneous kernel changes
    • MinWin
      • Change how Windows is built
      • Lots of DLL refactoring
      • API Sets (virtual DLLs)
    • Working-set management
      • Runaway processes quickly start reusing own pages
      • Break up kernel working-set into multiple working-sets
        • System cache, paged pool, pageable system code
    • Security
      • Better UAC, new account types, less BitLocker blockers
    • Energy efficiency
      • Trigger-started background services
      • Core Parking
      • Timer-coalescing, tick skipping
  • Major scalability improvements for large server apps
    • Broke apart last two major kernel locks, >64p
  • Kernel support for ConcRT
    • User-Mode Scheduling (UMS)

Copyright Microsoft Corporation

minwin
MinWin
  • MinWin is first step at creating architectural partitions
    • Can be built, booted and tested separately from the rest of the system
    • Higher layers can evolve independently
    • An engineering process improvement, not a microkernel NT!
  • MinWin was defined as set of components required to boot and access network
    • Kernel, file system driver, TCP/IP stack, device drivers, services
    • No servicing, WMI, graphics, audio or shell, etc, etc, etc
  • MinWin footprint:
    • 150 binaries, 25MB on disk, 40MB in-memory
minwin layering
MinWin Layering

Shell,

Graphics,

Multimedia,

Layered Services,

Applets,

Etc.

Kernel,

HAL,

TCP/IP,

File Systems,

Drivers,

Core System Services

MinWin

timer coalescing
Timer Coalescing
  • Secret of energy efficiency: Go idle and Stay idle
  • Staying idle requires minimizing timer interrupts
  • Before, periodic timers had independent cycles even when period was the same
  • New timer APIs permit timer coalescing
    • Application or driver specifies tolerable delay
    • Timer system shifts timer firing

Timer tick

15.6 ms

Vista

Periodic Timer Events

Windows 7

MarkRuss

broke apart the dispatcher lock
Broke apart the Dispatcher Lock
  • Scheduler Dispatcher lock hottest on server workloads
    • Lock protects all thread state changes (wait, unwait)
    • Very lock at >64x
  • Dispatcher lock broken up in Windows 7 / Server 2008 R2
    • Each object protected by its own lock
    • Many operations are lock-free

hot

Copyright Microsoft Corporation

removed pfn lock
Removed PFN Lock
  • Windows tracks the state of pages in physical memory
    • In use: in working sets:
    • Not assigned: on paging lists: freemodified, standby, …
  • Before, all page state changes protected by global PFN (Physical Frame Number) lock
  • As of Windows 7 the PFN lock is gone
    • Pages are now locked individually
    • Improves scalability for large memory applications

Copyright Microsoft Corporation

the silicon power wall
The Silicon Power Wall

The situation:

  • Power2∝ Clock frequency
  • Voltage ∝ Power2
    • Clock frequency and Voltage offset each other
  • Clock frequency inversely proportional to logic path length

Bad News:

  • Power is about as low as it can go
  • Logic paths between clocked elements are pretty short

Good News:

  • Moore’s Law continues (# transistors doubles ~22 months)
  • All that parallel computational theory is going into practice

Transistors going into more cores, not faster cores!

Software subject to Amdahl’s Law, not Moore’s Law

(or Gustafson’s Law

– if my wife can find large enough datasets she cares about)

17

approaches to hw parallelism
Approaches to HW parallelism

Homogeneous

More big superscalar cores

  • Extend with private (or shared) SIMD engines (SSE on steroids)
  • (Maybe) not very energy efficient

A few more big, cores and lots of smaller, slower, cooler cores

  • Use SIMD for performance
  • Shutoff idle small cores for energy efficiency (but leakage?)

Lots of little fully programmable cores, all the same

  • Nobody has ever gotten this to work – more on this later

Heterogeneous

Programmable Accelerators (e.g. GPUs)

  • Attach loosely-coupled, specialized (non-x86), energy-efficient cores

Fixed-function Accelerators

  • Very energy-efficient, device-like computational units for very-specific tasks

18

user mode scheduling ums
User Mode Scheduling (UMS)
  • Improve support for efficient cooperative multithreaded scheduling of small tasks (over-decomposition)
      • Want to schedule tasks in user-mode
      • Use NT threads to simulate CPUs, multiplex tasks onto these threads
  • When a task calls into the kernel and blocks, the CPU may get scheduled to a different app
      • If a single NT thread per CPU, when it blocks it blocks.
      • Could have extra threads, but then kernel and user-mode are competing to schedule the CPU
  • Tasks run arbitrary Win32 code (but only x64/IA64)
      • Assumes running on an NT thread (TEB, kernel thread)
  • Used by ConcRT (Visual Studio 2010’s Concurrency Run-Time)

Copyright Microsoft Corporation

windows 7 user mode scheduling
Windows 7 User-Mode Scheduling
  • UMS breaks NT thread into two parts:
    • UT: user-mode portion (TEB, ustack, registers)
    • KT: kernel-mode portion (ETHREAD, kstack, registers)
  • Three key properties:
    • User-mode scheduler switches UTs w/o ring crossing
    • KT switch is lazy: at kernel entry (e.g. syscall, pagefault)
    • CPU returned to user-mode scheduler when KT blocks
  • KT “returns” to user-mode by queuing completion
    • User-mode scheduler schedules corresponding UT
    • (similar to scheduler activations, etc)

Copyright Microsoft Corporation

normal nt threading
Normal NT Threading

x86 core

Kernel-mode

Scheduler

NTOS executive

KT0

KT1

KT2

kernel

trap code

user

UT0

UT1

UT2

  • NT Thread is Kernel Thread (KT) and User Thread (UT)
  • UT/KT form a single logical thread representing NT thread in user or kernel
    • KT: ETHREAD, KSTACK, link to EPROCESS
    • UT: TEB, USTACK

Copyright Microsoft Corporation

user mode scheduling ums22
User-Mode Scheduling (UMS)

NTOS executive

KT0 blocks

KT0

KT1

KT2

Primary

Thread

trap code

Thread Parking

kernel

user

UT Completion list

UT0

User-mode

Scheduler

Only primary thread runs in user-mode

Trap code switches to parked KT

KT blocks  primary returns to user-mode

KT unblocks & parks  queue UT completion

UT0

UT1

Copyright Microsoft Corporation

slide23
UMS
  • Based on NT threads
      • Each NT thread has user & kernel parts (UT & KT)
      • When a thread becomes UMS, KT never returns to UT
        • (Well, sort of)
      • Instead, the primary thread calls the USched
  • USched
      • Switches between UTs, all in user-mode
      • When a UT enters kernel and blocks, the primary thread will hand CPU back to the USched declaring UT blocked
      • When UT unblocks, kernel queues notification
      • USched consumes notifications, marks UT runnable
  • Primary Thread
      • Self-identified by entering kernel with wrong TEB
      • So UTs can migrate between threads
      • Affinities of primaries and KTs are orthogonal issues

Copyright Microsoft Corporation

ums thread roles
UMS Thread Roles
  • Primary threads: represent CPUs, normal app threads enter the USched world and become primaries, primaries also can be created by UScheds to allow parallel execution
    • Primaries represent concurrent execution
  • UMS threads (UT/KTs): allow blocking in the kernel without losing the CPU
    • UMS thread represent concurrent blocking in kernel

Copyright Microsoft Corporation

thread scheduling vs ums
Thread Scheduling vs UMS

User

Thread

4

User

Thread

3

User

Thread

5

User

Thread

6

Core 2

Core 2

Core 1

Core 1

Thread

4

Thread

5

User

Thread

1

Thread

1

Thread

3

Thread

2

Thread

6

User

Thread

2

Kernel

Thread

1

Kernel

Thread

2

Kernel

Thread

4

Kernel

Thread

3

Kernel

Thread

5

Kernel

Thread

6

Non-running threads

Thread Scheduling

Cooperative Scheduling

MarkRuss

win32 compat considerations
Win32 compat considerations

Why not Win32 fibers?

  • TEB issues
      • Contains TLS and Win32-specific fields (inclLastError)
      • Fibers run on multiple threads, so TEB state doesn’t track
  • Kernel thread issues
      • Visibility to TEB
      • I/O is queued to thread
      • Mutexes record thread owner
      • Impersonation
      • Cross-thread operations expect to find threads and IDs
      • Win32 code has thread and affinity awareness

Copyright Microsoft Corporation

futures master slave ums
Futures: Master/Slave UMS?

x86 core

Kernel-mode

Scheduler

NTOS executive

KT0

KT1

KT2

remote kernel

trap code

Thread Parking

Syscall Request Queue

Syscall Completion Queue

Remote x86

Remote

Scheduler

UT0

UTs (can) run on accelerators or x86s

KTs run on x86s, syscalls remoted/batched

Pagefaults are just like syscalls

Accelerator never “loses the CPU” (implicit primary)

UT2

UT1

Copyright Microsoft Corporation

operating systems futures
Operating Systems Futures
  • Many-core challenge
    • New driving force in software innovation:

Amdahl’s Law overtakes Moore’s Law as high-order bit

    • Heterogeneous cores?
  • OS Scalability
    • Loosely –coupled OS: mem + cpu + services?
    • Energy efficiency
  • Shrink-wrap and Freeze-dry applications?
  • Hypervisor/Kernel/Runtime relationships
    • Move kernel scheduling (cpu/memory) into run-times?
    • Move kernel resource management into Hypervisor?

Copyright Microsoft Corporation

windows academic program
Windows Academic Program
  • Windows Kernel Internals
    • Windows kernel in source (Windows Research Kernel – WRK)
    • Windows kernel in PowerPoint (Curriculum Resource Kit – CRK)
  • Based on Windows Server 2008 Service Pack 1
    • Latest kernel at time of release
    • First kernel release with AMD64 support
  • Joint program between Windows Product Group and MS Academic Groups
    • Program directed by Arkady Retik (Need a DVD? Have questions?)

Information available at

      • http://microsoft.com/WindowsAcademic OR
      • compsci@microsoft.com
  • Microsoft Academic Contacts in Buenos Aires

Miguel Saez (masaez@microsoft.com) or

Ezequiel Glinsky (eglinsky@microsoft.com)

Copyright Microsoft Corporation