Speed Up Synchronization Locks: How and Why?

Speed Up Synchronization Locks: A Scaleform Case Study Abhishek Agrawal Software Solutions Group

Legal Disclaimer ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Why care for Locking ?? ,[object Object],[object Object],[object Object],Proper use of locks is crucial for multi-threading applications

Common Lock Pathologies ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

How to avoid Lock Pathologies ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Use Atomic Operations and User-Level Locks

Windows* Locking Methodologies ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

WaitForSingleObject Vs. EnterCriticalSection ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],EnterCriticalSection WaitForSingleObject

EnterCriticalSection Vs. WaitForSingleObject ,[object Object],[object Object],Timings for the sample memory management kernel for 1 and 2 threads. Timings for the sample memory management kernel for 1 to 64 threads. Performance tests and ratings are measured using specific computer systems and/or components and reflect the approximate performance of Intel products as measured by those tests. Any difference in system hardware or software design or configuration may affect actual performance. Buyers should consult other sources of information to evaluate the performance of systems or components they are considering purchasing. For more information on performance tests and on the performance of Intel products, visit Intel Performance Benchmark Limitations (http://www.intel.com/performance/resources/limits.htm)

Where is the Performance Hit ?? ,[object Object],[object Object],[object Object],User Level Locks should be used for Granular Operations and in High Contention Scenarios

User Level Atomic Locks ,[object Object],[object Object],[object Object]

A Sample User Level Atomic Lock ,[object Object],Is it necessary to write assembly to take advantage of user land locks which utilize the lock prefix ??

Windows Interlocked Functions ,[object Object],[object Object],[object Object]

Atomic Lock (Performance Comparison) ,[object Object],[object Object],Cost of user-level atomic lock vs. WaitForSingleObject for the memory management locking kernel example Performance tests and ratings are measured using specific computer systems and/or components and reflect the approximate performance of Intel products as measured by those tests. Any difference in system hardware or software design or configuration may affect actual performance. Buyers should consult other sources of information to evaluate the performance of systems or components they are considering purchasing. For more information on performance tests and on the performance of Intel products, visit Intel Performance Benchmark Limitations (http://www.intel.com/performance/resources/limits.htm)

Scaleform* ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Why Is Threaded UI Important ?? ,[object Object]

Scaleform* Case Study Summary ,[object Object],[object Object],[object Object],[object Object],[object Object]

Using Fast Locks in Scaleform* volatile DWORD LockedThreadId = 0; void GLock::Lock() { DWORD threadId = GetCurrentThreadId(); if (threadId != LockedThreadId) { if ( (LockedThreadId == 0) && (InterlockedCompareExchange((long*)&LockedThreadId, threadId, 0) == 0 ) ) { // Single instruction atomic quick-lock was successful. } else { // Potentially locked elsewhere, so do a more expensive // lock with system wait on semaphore. PerfLock(threadId); } } RecursiveLockCount++; } void GLock::Unlock() { if (--RecursiveLockCount == 0) { // Release lock does not need atomic op on Intel Architecture! LockedThreadId = 0; // Release other system semaphore waiters, if any. } }

Scaleform GFx* Multi-threaded Demo ,[object Object],[object Object]

Finding Lock Contention Using Intel Tools ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Please refer to Intel Session on “Comparative Analysis of Game Parallelization” for more details on Thread Profiler

Contention using VTune™ (Where to Look) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Contention in WaitForSingleObject using VTune™ ,[object Object]

Possible Ways to Reduce Lock Contention ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Microsoft Flight Simulator* Case Study ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],Locking Problem Main Thread BKG Thread Main Thread BKG Thread

Locking Root-Cause ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Flight Simulator* Result ,[object Object],[object Object]

Synchronization Primitives in Intel TBB ® ,[object Object],[object Object],[object Object],[object Object],[object Object],No No Yes Yes queuing_rw_mutex No No No No spin_rw_mutex No No Yes Yes queuing_mutex No No No No spin_mutex Yes No OS dependent OS dependent mutex Sleeps Reentrant Fair Scalable

Example TBB ® Reader-Writer Lock ,[object Object],[object Object],#include “tbb/spin_rw_mutex.h” using namespace tbb; spin_rw_mutex MyMutex; int foo (){ /* Construction of ‘lock’ acquires ‘MyMutex’ */ spin_rw_mutex::scoped_lock lock (MyMutex, /*is_writer*/ false); … if (!lock.upgrade_to_writer ()) { /*data may have been modified since the last read*/ } else { /* data was not modified by other thread */ } return 0; /* Destructor of ‘lock’ releases ‘MyMutex’ */ }

General Recommendations for TBB ® Locks ,[object Object],[object Object],[object Object],Please refer to Intel Session on “Comparative Analysis of Game Parallelization” for more details on TBB

Summary & Call to Action ,[object Object],[object Object],[object Object],[object Object]

Contact Info ,[object Object],[object Object]

Speed Up Synchronization Locks: How and Why?

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Speed Up Synchronization Locks: How and Why?