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a3696c0b91
lib/sysdep: clean up by moving OS and cpu-arch folders into "os" and "arch" folders This was SVN commit r6162.
104 lines
3.2 KiB
C++
104 lines
3.2 KiB
C++
/**
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* =========================================================================
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* File : counter.cpp
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* Project : 0 A.D.
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* Description : Interface for counter implementations
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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#include "precompiled.h"
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#include "counter.h"
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#include "lib/bits.h"
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#include "lib/sysdep/cpu.h" // cpu_CAS
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#include "tsc.h"
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#include "hpet.h"
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#include "pmt.h"
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#include "qpc.h"
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#include "tgt.h"
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// to add a new counter type, simply include its header here and
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// insert a case in ConstructCounterAt's switch statement.
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//-----------------------------------------------------------------------------
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// create/destroy counters
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/**
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* @return pointer to a newly constructed ICounter subclass of type <id> at
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* the given address, or 0 iff the ID is invalid.
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* @param size maximum allowable size [bytes] of the subclass instance
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**/
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static ICounter* ConstructCounterAt(size_t id, void* address, size_t size)
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{
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// rationale for placement new: see call site.
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// counters are chosen according to the following order. rationale:
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// - TSC must come before QPC and PMT to make sure a bug in the latter on
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// Pentium systems doesn't come up.
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// - PMT works, but is inexplicably slower than QPC on a PIII Mobile.
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// - TGT really isn't as safe as the others, so it should be last.
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// - low-overhead and high-resolution counters are preferred.
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switch(id)
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{
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case 0:
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debug_assert(sizeof(CounterHPET) <= size);
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return new(address) CounterHPET();
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case 1:
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debug_assert(sizeof(CounterTSC) <= size);
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return new(address) CounterTSC();
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case 2:
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debug_assert(sizeof(CounterQPC) <= size);
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return new(address) CounterQPC();
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case 3:
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debug_assert(sizeof(CounterPMT) <= size);
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return new(address) CounterPMT();
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case 4:
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debug_assert(sizeof(CounterTGT) <= size);
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return new(address) CounterTGT();
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default:
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return 0;
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}
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}
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static volatile uintptr_t isCounterAllocated;
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ICounter* CreateCounter(size_t id)
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{
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// we placement-new the Counter classes in a static buffer.
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// this is dangerous, but we are careful to ensure alignment. it is
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// unusual and thus bad, but there's also one advantage: we avoid
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// using global operator new before the CRT is initialized (risky).
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//
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// alternatives:
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// - defining as static doesn't work because the ctors (necessary for
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// vptr initialization) run during _cinit, which comes after our
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// first use of them.
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// - using static_calloc isn't possible because we don't know the
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// size until after the alloc / placement new.
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if(!cpu_CAS(&isCounterAllocated, 0, 1))
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debug_assert(0); // static counter memory is already in use!
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static const size_t memSize = 200;
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static u8 mem[memSize];
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u8* alignedMem = (u8*)round_up((uintptr_t)mem, (uintptr_t)16u);
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const size_t bytesLeft = mem+memSize - alignedMem;
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ICounter* counter = ConstructCounterAt(id, alignedMem, bytesLeft);
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return counter;
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}
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void DestroyCounter(ICounter*& counter)
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{
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debug_assert(counter);
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counter->Shutdown();
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counter->~ICounter(); // must be called due to placement new
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counter = 0;
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isCounterAllocated = 0;
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}
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