From 29d3e89b71281c626f151a1585a40d9d2448123b Mon Sep 17 00:00:00 2001
From: rpj <rpj>
Date: Tue, 26 Apr 2005 02:41:11 +0000
Subject: ''

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 tests/README.BENCHTESTS | 97 +++++++++++++++++++++++++++++++++++++++++++++++++
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 create mode 100644 tests/README.BENCHTESTS

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diff --git a/tests/README.BENCHTESTS b/tests/README.BENCHTESTS
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+
+------------
+Benchmarking
+------------
+There is a new but growing set a benchmarking programs in the
+"tests" directory. These should be runnable using the
+following command-lines corresponding to each of the possible
+library builds:
+
+MSVC:
+nmake clean VC-bench
+nmake clean VCE-bench
+nmake clean VSE-bench
+
+Mingw32:
+make clean GC-bench
+make clean GCE-bench
+
+UWIN:
+The benchtests are run as part of the testsuite.
+
+
+Mutex benchtests
+----------------
+
+benchtest1 - Lock plus unlock on an unlocked mutex.
+benchtest2 - Lock plus unlock on a locked mutex.
+benchtest3 - Trylock on a locked mutex.
+benchtest4 - Trylock plus unlock on an unlocked mutex.
+
+
+Each test times up to three alternate synchronisation
+implementations as a reference, and then times each of
+the four mutex types provided by the library. Each is
+described below:
+
+Simple Critical Section
+- uses a simple Win32 critical section. There is no
+additional overhead for this case as there is in the
+remaining cases.
+
+POSIX mutex implemented using a Critical Section
+- The old implementation which uses runtime adaptation
+depending on the Windows variant being run on. When
+the pthreads DLL was run on WinNT or higher then
+POSIX mutexes would use Win32 Critical Sections.
+
+POSIX mutex implemented using a Win32 Mutex
+- The old implementation which uses runtime adaptation
+depending on the Windows variant being run on. When
+the pthreads DLL was run on Win9x then POSIX mutexes
+would use Win32 Mutexes (because TryEnterCriticalSection
+is not implemented on Win9x).
+
+PTHREAD_MUTEX_DEFAULT
+PTHREAD_MUTEX_NORMAL
+PTHREAD_MUTEX_ERRORCHECK
+PTHREAD_MUTEX_RECURSIVE
+- The current implementation supports these mutex types.
+The underlying basis of POSIX mutexes is now the same
+irrespective of the Windows variant, and should therefore
+have consistent performance.
+
+
+In all benchtests, the operation is repeated a large
+number of times and an average is calculated. Loop
+overhead is measured and subtracted from all test times.
+
+Comment on the results
+----------------------
+The gain in performance for Win9x systems is enormous - up to
+40 times faster for unlocked mutexes (2 times faster for locked
+mutexes).
+
+Pthread_mutex_trylock also appears to be faster for locked mutexes.
+
+The price for the new consistency between WinNT and Win9x is
+slower performance (up to twice as long) across a lock/unlock
+sequence. It is difficult to get a good split timing for lock
+and unlock operations, but by code inspection, it is the unlock
+operation that is slowing the pair down in comparison with the
+old-style CS mutexes, even for the fast PTHREAD_MUTEX_NORMAL mutex
+type with no other waiting threads. However, comparitive
+performance for operations on already locked mutexes is very close.
+
+When this is translated to real-world applications, the overall
+camparitive performance should be almost identical on NT class
+systems. That is, applications with heavy mutex contention should
+have almost equal performance, while applications with only light
+mutex contention should also have almost equal performance because
+the most critical operation in this case is the lock operation.
+
+Overall, the newer pthreads-win32 mutex routines are only slower
+(on NT class systems) where and when it is least critical.
+
+Thanks go to Thomas Pfaff for the current implementation of mutex
+routines.
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