DiskCacheGovernor.h

Go to the documentation of this file.

// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Misc/CoreMiscDefines.h"
#include <atomic>
 
namespace UE::IoStore
{
 
class FDiskCacheGovernor
{
public:
    struct FAllowance
    {
        uint32  Bytes = 16 << 20;
        uint32  Ops = 32;
        uint32  Seconds = 60;
    };
 
    struct FDemand
    {
        uint8   Threshold = 30;
        uint8   Boost = 60;
        uint8   SuperBoost = 87;
    };
 
    struct FConfig
    {
        FAllowance  Allowance;
        FDemand     Demand;
        uint32      CommitBufferSize = 0;
    };
 
            FDiskCacheGovernor();
            UE_NONCOPYABLE(FDiskCacheGovernor);
 
    void    ConfigureStreamingCache(const FConfig& Config);
    int32   TryBeginWriteToStreamingCache(uint32 DemandPercent);
    int32   EndWriteToStreamingCache(uint32 UnusedAllowance);
    void    OnInstallCacheFlushed(uint64 ByteCount, uint32 OpCount);
 
private:
    struct FCacheState;
 
    static void     Configure(FCacheState& CacheState, const FConfig& Config);
    static int32    TryBeginWrite(FCacheState& CacheState, uint32 DemandPercent, int64 Cycles);
    static int32    TryBeginWrite(FCacheState& CacheState, uint32 DemandPercent);
    static int32    EndWrite(struct FCacheState& CacheState, uint32 UnusedAllowance);
    static int32    GetMaxWaitCycles(FCacheState& CacheState);
 
    struct FCacheState
    {
        enum class EState : uint8
        {
            Waiting,
            Rolling,
        };
 
        int64               OpInterval = 0;
        int64               PrevCycles = 0;
        uint32              RunOff = 0;
        uint32              OpCount = 0;
        uint32              MaxOpCount = 0;
        uint32              OpAllowance = 0;
        std::atomic_int64_t CyclesSuspended{0};
        FDemand             Demand;
        EState              State = EState::Waiting;
    };
 
    FCacheState StreamingCacheState;
};
 
} // namespace UE::IoStore