diff --git a/Core/Config.cpp b/Core/Config.cpp
index c7b194a3a3..4dc64d8518 100644
--- a/Core/Config.cpp
+++ b/Core/Config.cpp
@@ -1838,7 +1838,7 @@ int Config::GetPSPLanguage() {
 	}
 }
 
-void PlayTimeTracker::Start(std::string gameId) {
+void PlayTimeTracker::Start(const std::string &gameId) {
 	if (gameId.empty()) {
 		return;
 	}
@@ -1860,7 +1860,7 @@ void PlayTimeTracker::Start(std::string gameId) {
 	tracker_[gameId] = playTime;
 }
 
-void PlayTimeTracker::Stop(std::string gameId) {
+void PlayTimeTracker::Stop(const std::string &gameId) {
 	if (gameId.empty()) {
 		return;
 	}
diff --git a/Core/Config.h b/Core/Config.h
index de2d6971cb..6a2114391c 100644
--- a/Core/Config.h
+++ b/Core/Config.h
@@ -48,8 +48,8 @@ public:
 	};
 
 	// It's OK to call these redundantly.
-	void Start(std::string gameId);
-	void Stop(std::string gameId);
+	void Start(const std::string &gameId);
+	void Stop(const std::string &gameId);
 
 	void Load(const Section *section);
 	void Save(Section *section);
diff --git a/Core/Core.cpp b/Core/Core.cpp
index 36f9fd0f83..ef7ca4e94d 100644
--- a/Core/Core.cpp
+++ b/Core/Core.cpp
@@ -418,7 +418,7 @@ void Core_MemoryException(u32 address, u32 accessSize, u32 pc, MemoryExceptionTy
 	}
 }
 
-void Core_MemoryExceptionInfo(u32 address, u32 accessSize, u32 pc, MemoryExceptionType type, std::string additionalInfo, bool forceReport) {
+void Core_MemoryExceptionInfo(u32 address, u32 accessSize, u32 pc, MemoryExceptionType type, const std::string &additionalInfo, bool forceReport) {
 	const char *desc = MemoryExceptionTypeAsString(type);
 	// In jit, we only flush PC when bIgnoreBadMemAccess is off.
 	if ((g_Config.iCpuCore == (int)CPUCore::JIT || g_Config.iCpuCore == (int)CPUCore::JIT_IR) && g_Config.bIgnoreBadMemAccess) {
diff --git a/Core/Core.h b/Core/Core.h
index 9024214c5d..42caf85996 100644
--- a/Core/Core.h
+++ b/Core/Core.h
@@ -105,7 +105,7 @@ enum class ExecExceptionType {
 // Separate one for without info, to avoid having to allocate a string
 void Core_MemoryException(u32 address, u32 accessSize, u32 pc, MemoryExceptionType type);
 
-void Core_MemoryExceptionInfo(u32 address, u32 accessSize, u32 pc, MemoryExceptionType type, std::string additionalInfo, bool forceReport);
+void Core_MemoryExceptionInfo(u32 address, u32 accessSize, u32 pc, MemoryExceptionType type, const std::string &additionalInfo, bool forceReport);
 
 void Core_ExecException(u32 address, u32 pc, ExecExceptionType type);
 void Core_Break(u32 pc);
diff --git a/Core/Debugger/DisassemblyManager.cpp b/Core/Debugger/DisassemblyManager.cpp
index ecea54a868..7b1c7f4c4b 100644
--- a/Core/Debugger/DisassemblyManager.cpp
+++ b/Core/Debugger/DisassemblyManager.cpp
@@ -820,7 +820,7 @@ void DisassemblyMacro::setMacroLi(u32 _immediate, u8 _rt)
 	numOpcodes = 2;
 }
 
-void DisassemblyMacro::setMacroMemory(std::string _name, u32 _immediate, u8 _rt, int _dataSize)
+void DisassemblyMacro::setMacroMemory(const std::string &_name, u32 _immediate, u8 _rt, int _dataSize)
 {
 	type = MACRO_MEMORYIMM;
 	name = _name;
diff --git a/Core/Debugger/DisassemblyManager.h b/Core/Debugger/DisassemblyManager.h
index 81520818b1..c0f990d853 100644
--- a/Core/Debugger/DisassemblyManager.h
+++ b/Core/Debugger/DisassemblyManager.h
@@ -120,7 +120,7 @@ public:
 	DisassemblyMacro(u32 _address): address(_address) { }
 
 	void setMacroLi(u32 _immediate, u8 _rt);
-	void setMacroMemory(std::string _name, u32 _immediate, u8 _rt, int _dataSize);
+	void setMacroMemory(const std::string &_name, u32 _immediate, u8 _rt, int _dataSize);
 
 	void recheck() override { };
 	int getNumLines() override { return 1; };
diff --git a/Core/Dialog/PSPGamedataInstallDialog.cpp b/Core/Dialog/PSPGamedataInstallDialog.cpp
index 84cef563d9..3ce0f30ff2 100644
--- a/Core/Dialog/PSPGamedataInstallDialog.cpp
+++ b/Core/Dialog/PSPGamedataInstallDialog.cpp
@@ -49,7 +49,7 @@ static const std::string SFO_FILENAME = "PARAM.SFO";
 
 namespace
 {
-	std::vector<std::string> GetPSPFileList (std::string dirpath) {
+	std::vector<std::string> GetPSPFileList (const std::string &dirpath) {
 		std::vector<std::string> FileList;
 		auto Fileinfos = pspFileSystem.GetDirListing(dirpath);
 
@@ -258,7 +258,7 @@ int PSPGamedataInstallDialog::Shutdown(bool force) {
 	return PSPDialog::Shutdown(force);
 }
 
-std::string PSPGamedataInstallDialog::GetGameDataInstallFileName(const SceUtilityGamedataInstallParam *param, std::string filename) {
+std::string PSPGamedataInstallDialog::GetGameDataInstallFileName(const SceUtilityGamedataInstallParam *param, const std::string &filename) {
 	if (!param)
 		return "";
 	std::string GameDataInstallPath = saveBasePath + param->gameName + param->dataName + "/";
diff --git a/Core/Dialog/PSPGamedataInstallDialog.h b/Core/Dialog/PSPGamedataInstallDialog.h
index bf076c751e..859d9a3d72 100644
--- a/Core/Dialog/PSPGamedataInstallDialog.h
+++ b/Core/Dialog/PSPGamedataInstallDialog.h
@@ -44,7 +44,7 @@ public:
 	void DoState(PointerWrap &p) override;
 
 	int Abort();
-	std::string GetGameDataInstallFileName(const SceUtilityGamedataInstallParam *param, std::string filename);
+	std::string GetGameDataInstallFileName(const SceUtilityGamedataInstallParam *param, const std::string &filename);
 
 protected:
 	// TODO: Manage status correctly.
diff --git a/Core/Dialog/PSPMsgDialog.cpp b/Core/Dialog/PSPMsgDialog.cpp
index 3722d89faf..6b23fde60b 100755
--- a/Core/Dialog/PSPMsgDialog.cpp
+++ b/Core/Dialog/PSPMsgDialog.cpp
@@ -179,7 +179,7 @@ void PSPMsgDialog::FormatErrorCode(uint32_t code) {
 	}
 }
 
-void PSPMsgDialog::DisplayMessage(std::string text, bool hasYesNo, bool hasOK) {
+void PSPMsgDialog::DisplayMessage(const std::string &text, bool hasYesNo, bool hasOK) {
 	auto di = GetI18NCategory(I18NCat::DIALOG);
 
 	PPGeStyle buttonStyle = FadedStyle(PPGeAlign::BOX_CENTER, FONT_SCALE);
diff --git a/Core/Dialog/PSPMsgDialog.h b/Core/Dialog/PSPMsgDialog.h
index 32a4831640..6291cf3648 100644
--- a/Core/Dialog/PSPMsgDialog.h
+++ b/Core/Dialog/PSPMsgDialog.h
@@ -76,7 +76,7 @@ protected:
 
 private:
 	void FormatErrorCode(uint32_t code);
-	void DisplayMessage(std::string text, bool hasYesNo = false, bool hasOK = false);
+	void DisplayMessage(const std::string &text, bool hasYesNo = false, bool hasOK = false);
 
 	enum Flags
 	{
diff --git a/Core/Dialog/PSPNetconfDialog.cpp b/Core/Dialog/PSPNetconfDialog.cpp
index 70b1a41511..c1802db9e7 100644
--- a/Core/Dialog/PSPNetconfDialog.cpp
+++ b/Core/Dialog/PSPNetconfDialog.cpp
@@ -103,7 +103,7 @@ void PSPNetconfDialog::DrawIndicator() {
 	PPGeDrawImage(456, 248, 20.0f, 20.0f, 1, 10, 1, 10, 10, 10, FadedImageStyle());
 }
 
-void PSPNetconfDialog::DisplayMessage(std::string text1, std::string text2a, std::string text2b, std::string text3a, std::string text3b, bool hasYesNo, bool hasOK) {
+void PSPNetconfDialog::DisplayMessage(const std::string &text1, const std::string &text2a, const std::string &text2b, const std::string &text3a, const std::string &text3b, bool hasYesNo, bool hasOK) {
 	auto di = GetI18NCategory(I18NCat::DIALOG);
 
 	PPGeStyle buttonStyle = FadedStyle(PPGeAlign::BOX_CENTER, FONT_SCALE);
diff --git a/Core/Dialog/PSPNetconfDialog.h b/Core/Dialog/PSPNetconfDialog.h
index 52a3ce203a..e2d06f3739 100644
--- a/Core/Dialog/PSPNetconfDialog.h
+++ b/Core/Dialog/PSPNetconfDialog.h
@@ -52,7 +52,7 @@ protected:
 	}
 
 private:
-	void DisplayMessage(std::string text1, std::string text2a = "", std::string text2b = "", std::string text3a = "", std::string text3b = "", bool hasYesNo = false, bool hasOK = false);
+	void DisplayMessage(const std::string &text1, const std::string &text2a = "", const std::string &text2b = "", const std::string &text3a = "", const std::string &text3b = "", bool hasYesNo = false, bool hasOK = false);
 	void DrawBanner();
 	void DrawIndicator();
 
diff --git a/Core/Dialog/PSPNpSigninDialog.cpp b/Core/Dialog/PSPNpSigninDialog.cpp
index bc8def540e..9af12480c9 100644
--- a/Core/Dialog/PSPNpSigninDialog.cpp
+++ b/Core/Dialog/PSPNpSigninDialog.cpp
@@ -100,7 +100,7 @@ void PSPNpSigninDialog::DrawLogo() {
 	PPGeDrawImage(416, 22, 64.0f, 64.0f, 1, 10, 1, 10, 64, 64, FadedImageStyle());
 }
 
-void PSPNpSigninDialog::DisplayMessage(std::string text1, std::string text2a, std::string text2b, std::string text3a, std::string text3b, bool hasYesNo, bool hasOK) {
+void PSPNpSigninDialog::DisplayMessage(const std::string &text1, const std::string &text2a, const std::string &text2b, const std::string &text3a, const std::string &text3b, bool hasYesNo, bool hasOK) {
 	auto di = GetI18NCategory(I18NCat::DIALOG);
 
 	PPGeStyle buttonStyle = FadedStyle(PPGeAlign::BOX_CENTER, FONT_SCALE);
diff --git a/Core/Dialog/PSPNpSigninDialog.h b/Core/Dialog/PSPNpSigninDialog.h
index 2b31922735..5b67b508da 100644
--- a/Core/Dialog/PSPNpSigninDialog.h
+++ b/Core/Dialog/PSPNpSigninDialog.h
@@ -48,7 +48,7 @@ protected:
 	}
 
 private:
-	void DisplayMessage(std::string text1, std::string text2a = "", std::string text2b = "", std::string text3a = "", std::string text3b = "", bool hasYesNo = false, bool hasOK = false);
+	void DisplayMessage(const std::string &text1, const std::string &text2a = "", const std::string &text2b = "", const std::string &text3a = "", const std::string &text3b = "", bool hasYesNo = false, bool hasOK = false);
 	void DrawBanner();
 	void DrawIndicator();
 	void DrawLogo();
diff --git a/Core/Dialog/PSPSaveDialog.cpp b/Core/Dialog/PSPSaveDialog.cpp
index ee388bef19..31f59b29be 100755
--- a/Core/Dialog/PSPSaveDialog.cpp
+++ b/Core/Dialog/PSPSaveDialog.cpp
@@ -580,7 +580,7 @@ void PSPSaveDialog::DisplaySaveDataInfo2(bool showNewData) {
 	PPGeDrawText(saveinfoTxt.c_str(), 8, 200, textStyle);
 }
 
-void PSPSaveDialog::DisplayMessage(std::string text, bool hasYesNo)
+void PSPSaveDialog::DisplayMessage(const std::string &text, bool hasYesNo)
 {
 	PPGeStyle textStyle = FadedStyle(PPGeAlign::BOX_CENTER, FONT_SCALE);
 
diff --git a/Core/Dialog/PSPSaveDialog.h b/Core/Dialog/PSPSaveDialog.h
index be6024ac52..d068a07a6b 100644
--- a/Core/Dialog/PSPSaveDialog.h
+++ b/Core/Dialog/PSPSaveDialog.h
@@ -94,7 +94,7 @@ private:
 	void DisplaySaveIcon(bool checkExists);
 	void DisplaySaveDataInfo1();
 	void DisplaySaveDataInfo2(bool showNewData = false);
-	void DisplayMessage(std::string text, bool hasYesNo = false);
+	void DisplayMessage(const std::string &text, bool hasYesNo = false);
 	const std::string GetSelectedSaveDirName() const;
 
 	void JoinIOThread();
diff --git a/Core/Dialog/SavedataParam.cpp b/Core/Dialog/SavedataParam.cpp
index 58f107b218..55437681fd 100644
--- a/Core/Dialog/SavedataParam.cpp
+++ b/Core/Dialog/SavedataParam.cpp
@@ -63,7 +63,7 @@ namespace
 		truncate_cpy(str, strLength, value.c_str());
 	}
 
-	bool ReadPSPFile(std::string filename, u8 **data, s64 dataSize, s64 *readSize)
+	bool ReadPSPFile(const std::string &filename, u8 **data, s64 dataSize, s64 *readSize)
 	{
 		int handle = pspFileSystem.OpenFile(filename, FILEACCESS_READ);
 		if (handle < 0)
@@ -86,7 +86,7 @@ namespace
 		return result != 0;
 	}
 
-	bool WritePSPFile(std::string filename, const u8 *data, SceSize dataSize)
+	bool WritePSPFile(const std::string &filename, const u8 *data, SceSize dataSize)
 	{
 		int handle = pspFileSystem.OpenFile(filename, (FileAccess)(FILEACCESS_WRITE | FILEACCESS_CREATE | FILEACCESS_TRUNCATE));
 		if (handle < 0)
@@ -110,7 +110,7 @@ namespace
 		return info;
 	}
 
-	bool PSPMatch(std::string text, std::string regexp)
+	bool PSPMatch(const std::string &text, const std::string &regexp)
 	{
 		if(text.empty() && regexp.empty())
 			return true;
@@ -1607,7 +1607,7 @@ int SavedataParam::SetPspParam(SceUtilitySavedataParam *param)
 	return 0;
 }
 
-void SavedataParam::SetFileInfo(SaveFileInfo &saveInfo, PSPFileInfo &info, std::string saveName, std::string savrDir)
+void SavedataParam::SetFileInfo(SaveFileInfo &saveInfo, PSPFileInfo &info, const std::string &saveName, const std::string &savrDir)
 {
 	saveInfo.size = info.size;
 	saveInfo.saveName = saveName;
@@ -1647,7 +1647,7 @@ void SavedataParam::SetFileInfo(SaveFileInfo &saveInfo, PSPFileInfo &info, std::
 	}
 }
 
-void SavedataParam::SetFileInfo(int idx, PSPFileInfo &info, std::string saveName, std::string saveDir)
+void SavedataParam::SetFileInfo(int idx, PSPFileInfo &info, const std::string &saveName, const std::string &saveDir)
 {
 	SetFileInfo(saveDataList[idx], info, saveName, saveDir);
 	saveDataList[idx].idx = idx;
@@ -1679,7 +1679,7 @@ void SavedataParam::ClearFileInfo(SaveFileInfo &saveInfo, const std::string &sav
 	}
 }
 
-PSPFileInfo SavedataParam::GetSaveInfo(std::string saveDir) {
+PSPFileInfo SavedataParam::GetSaveInfo(const std::string &saveDir) {
 	PSPFileInfo info = pspFileSystem.GetFileInfo(saveDir);
 	if (info.exists) {
 		info.access = 0777;
@@ -1970,7 +1970,7 @@ int SavedataParam::GetSaveCryptMode(const SceUtilitySavedataParam *param, const
 	return 0;
 }
 
-bool SavedataParam::IsInSaveDataList(std::string saveName, int count) {
+bool SavedataParam::IsInSaveDataList(const std::string &saveName, int count) {
 	for(int i = 0; i < count; ++i) {
 		if(strcmp(saveDataList[i].saveName.c_str(),saveName.c_str()) == 0)
 			return true;
diff --git a/Core/Dialog/SavedataParam.h b/Core/Dialog/SavedataParam.h
index 257fc02746..04c8dca5e4 100644
--- a/Core/Dialog/SavedataParam.h
+++ b/Core/Dialog/SavedataParam.h
@@ -318,7 +318,7 @@ public:
 	int GetFilesList(SceUtilitySavedataParam* param, u32 requestAddr);
 	bool GetSize(SceUtilitySavedataParam* param);
 	int GetSaveCryptMode(const SceUtilitySavedataParam *param, const std::string &saveDirName);
-	bool IsInSaveDataList(std::string saveName, int count);
+	bool IsInSaveDataList(const std::string &saveName, int count);
 
 	std::string GetGameName(const SceUtilitySavedataParam *param) const;
 	std::string GetSaveName(const SceUtilitySavedataParam *param) const;
@@ -361,10 +361,10 @@ public:
 
 private:
 	void Clear();
-	void SetFileInfo(int idx, PSPFileInfo &info, std::string saveName, std::string saveDir = "");
-	void SetFileInfo(SaveFileInfo &saveInfo, PSPFileInfo &info, std::string saveName, std::string saveDir = "");
+	void SetFileInfo(int idx, PSPFileInfo &info, const std::string &saveName, const std::string &saveDir = "");
+	void SetFileInfo(SaveFileInfo &saveInfo, PSPFileInfo &info, const std::string &saveName, const std::string &saveDir = "");
 	void ClearFileInfo(SaveFileInfo &saveInfo, const std::string &saveName);
-	PSPFileInfo GetSaveInfo(std::string saveDir);
+	PSPFileInfo GetSaveInfo(const std::string &saveDir);
 
 	int LoadSaveData(SceUtilitySavedataParam *param, const std::string &saveDirName, const std::string& dirPath, bool secureMode);
 	u32 LoadCryptedSave(SceUtilitySavedataParam *param, u8 *data, const u8 *saveData, int &saveSize, int prevCryptMode, const u8 *expectedHash, bool &saveDone);
diff --git a/Core/ELF/ParamSFO.cpp b/Core/ELF/ParamSFO.cpp
index d6717af0b2..3aeb92b7bf 100644
--- a/Core/ELF/ParamSFO.cpp
+++ b/Core/ELF/ParamSFO.cpp
@@ -43,38 +43,38 @@ struct IndexTable
 	u32_le data_table_offset; /* Offset of the param_data from start of data_table */
 };
 
-void ParamSFOData::SetValue(std::string key, unsigned int value, int max_size) {
+void ParamSFOData::SetValue(const std::string &key, unsigned int value, int max_size) {
 	values[key].type = VT_INT;
 	values[key].i_value = value;
 	values[key].max_size = max_size;
 }
-void ParamSFOData::SetValue(std::string key, std::string value, int max_size) {
+void ParamSFOData::SetValue(const std::string &key, const std::string &value, int max_size) {
 	values[key].type = VT_UTF8;
 	values[key].s_value = value;
 	values[key].max_size = max_size;
 }
 
-void ParamSFOData::SetValue(std::string key, const u8 *value, unsigned int size, int max_size) {
+void ParamSFOData::SetValue(const std::string &key, const u8 *value, unsigned int size, int max_size) {
 	values[key].type = VT_UTF8_SPE;
 	values[key].SetData(value, size);
 	values[key].max_size = max_size;
 }
 
-int ParamSFOData::GetValueInt(std::string key) const {
+int ParamSFOData::GetValueInt(const std::string &key) const {
 	std::map<std::string,ValueData>::const_iterator it = values.find(key);
 	if(it == values.end() || it->second.type != VT_INT)
 		return 0;
 	return it->second.i_value;
 }
 
-std::string ParamSFOData::GetValueString(std::string key) const {
+std::string ParamSFOData::GetValueString(const std::string &key) const {
 	std::map<std::string,ValueData>::const_iterator it = values.find(key);
 	if(it == values.end() || (it->second.type != VT_UTF8))
 		return "";
 	return it->second.s_value;
 }
 
-const u8 *ParamSFOData::GetValueData(std::string key, unsigned int *size) const {
+const u8 *ParamSFOData::GetValueData(const std::string &key, unsigned int *size) const {
 	std::map<std::string,ValueData>::const_iterator it = values.find(key);
 	if(it == values.end() || (it->second.type != VT_UTF8_SPE))
 		return 0;
@@ -195,7 +195,7 @@ bool ParamSFOData::ReadSFO(const u8 *paramsfo, size_t size) {
 	return true;
 }
 
-int ParamSFOData::GetDataOffset(const u8 *paramsfo, std::string dataName) {
+int ParamSFOData::GetDataOffset(const u8 *paramsfo, const std::string &dataName) {
 	const Header *header = (const Header *)paramsfo;
 	if (header->magic != 0x46535000)
 		return -1;
@@ -320,7 +320,7 @@ void ParamSFOData::ValueData::SetData(const u8* data, int size) {
 	u_size = size;
 }
 
-std::string ParamSFOData::GenerateFakeID(std::string filename) const {
+std::string ParamSFOData::GenerateFakeID(const std::string &filename) const {
 	// Generates fake gameID for homebrew based on it's folder name.
 	// Should probably not be a part of ParamSFO, but it'll be called in same places.
 	std::string file = PSP_CoreParameter().fileToStart.ToString();
diff --git a/Core/ELF/ParamSFO.h b/Core/ELF/ParamSFO.h
index 0e5afab4bd..f132e1c5f7 100644
--- a/Core/ELF/ParamSFO.h
+++ b/Core/ELF/ParamSFO.h
@@ -27,16 +27,16 @@
 class ParamSFOData
 {
 public:
-	void SetValue(std::string key, unsigned int value, int max_size);
-	void SetValue(std::string key, std::string value, int max_size);
-	void SetValue(std::string key, const u8 *value, unsigned int size, int max_size);
+	void SetValue(const std::string &key, unsigned int value, int max_size);
+	void SetValue(const std::string &key, const std::string &value, int max_size);
+	void SetValue(const std::string &key, const u8 *value, unsigned int size, int max_size);
 
-	int GetValueInt(std::string key) const;
-	std::string GetValueString(std::string key) const;
-	const u8 *GetValueData(std::string key, unsigned int *size) const;
+	int GetValueInt(const std::string &key) const;
+	std::string GetValueString(const std::string &key) const;
+	const u8 *GetValueData(const std::string &key, unsigned int *size) const;
 
 	std::vector<std::string> GetKeys() const;
-	std::string GenerateFakeID(std::string filename = "") const;
+	std::string GenerateFakeID(const std::string &filename = "") const;
 
 	std::string GetDiscID();
 
@@ -51,7 +51,7 @@ public:
 		}
 	}
 
-	int GetDataOffset(const u8 *paramsfo, std::string dataName);
+	int GetDataOffset(const u8 *paramsfo, const std::string &dataName);
 
 	void Clear();
 
diff --git a/Core/FileSystems/DirectoryFileSystem.cpp b/Core/FileSystems/DirectoryFileSystem.cpp
index 0ead3b15f7..7695653c03 100644
--- a/Core/FileSystems/DirectoryFileSystem.cpp
+++ b/Core/FileSystems/DirectoryFileSystem.cpp
@@ -966,7 +966,7 @@ VFSFileSystem::~VFSFileSystem() {
 	entries.clear();
 }
 
-std::string VFSFileSystem::GetLocalPath(std::string localPath) {
+std::string VFSFileSystem::GetLocalPath(const std::string &localPath) {
 	return basePath + localPath;
 }
 
diff --git a/Core/FileSystems/DirectoryFileSystem.h b/Core/FileSystems/DirectoryFileSystem.h
index 5edfa9a1a3..965a90f8fc 100644
--- a/Core/FileSystems/DirectoryFileSystem.h
+++ b/Core/FileSystems/DirectoryFileSystem.h
@@ -145,5 +145,5 @@ private:
 	std::string basePath;
 	IHandleAllocator *hAlloc;
 
-	std::string GetLocalPath(std::string localpath);
+	std::string GetLocalPath(const std::string &localpath);
 };
diff --git a/Core/FileSystems/ISOFileSystem.cpp b/Core/FileSystems/ISOFileSystem.cpp
index 06ebac25af..4fb682684e 100644
--- a/Core/FileSystems/ISOFileSystem.cpp
+++ b/Core/FileSystems/ISOFileSystem.cpp
@@ -30,7 +30,7 @@
 
 const int sectorSize = 2048;
 
-bool parseLBN(std::string filename, u32 *sectorStart, u32 *readSize) {
+bool parseLBN(const std::string &filename, u32 *sectorStart, u32 *readSize) {
 	// The format of this is: "/sce_lbn" "0x"? HEX* ANY* "_size" "0x"? HEX* ANY*
 	// That means that "/sce_lbn/_size1/" is perfectly valid.
 	// Most commonly, it looks like /sce_lbn0x10_size0x100 or /sce_lbn10_size100 (always hex.)
diff --git a/Core/FileSystems/ISOFileSystem.h b/Core/FileSystems/ISOFileSystem.h
index 613bfcf15d..be613bee93 100644
--- a/Core/FileSystems/ISOFileSystem.h
+++ b/Core/FileSystems/ISOFileSystem.h
@@ -25,7 +25,7 @@
 
 #include "BlockDevices.h"
 
-bool parseLBN(std::string filename, u32 *sectorStart, u32 *readSize);
+bool parseLBN(const std::string &filename, u32 *sectorStart, u32 *readSize);
 
 class ISOFileSystem : public IFileSystem {
 public:
diff --git a/Core/FileSystems/MetaFileSystem.cpp b/Core/FileSystems/MetaFileSystem.cpp
index c35f0e59ef..5dece8e210 100644
--- a/Core/FileSystems/MetaFileSystem.cpp
+++ b/Core/FileSystems/MetaFileSystem.cpp
@@ -274,7 +274,7 @@ std::string MetaFileSystem::NormalizePrefix(std::string prefix) const {
 	return prefix;
 }
 
-void MetaFileSystem::Mount(std::string prefix, std::shared_ptr<IFileSystem> system) {
+void MetaFileSystem::Mount(const std::string &prefix, std::shared_ptr<IFileSystem> system) {
 	std::lock_guard<std::recursive_mutex> guard(lock);
 
 	MountPoint x;
@@ -297,7 +297,7 @@ void MetaFileSystem::UnmountAll() {
 	currentDir.clear();
 }
 
-void MetaFileSystem::Unmount(std::string prefix) {
+void MetaFileSystem::Unmount(const std::string &prefix) {
 	for (auto iter = fileSystems.begin(); iter != fileSystems.end(); iter++) {
 		if (iter->prefix == prefix) {
 			fileSystems.erase(iter);
@@ -306,7 +306,7 @@ void MetaFileSystem::Unmount(std::string prefix) {
 	}
 }
 
-bool MetaFileSystem::Remount(std::string prefix, std::shared_ptr<IFileSystem> system) {
+bool MetaFileSystem::Remount(const std::string &prefix, std::shared_ptr<IFileSystem> system) {
 	std::lock_guard<std::recursive_mutex> guard(lock);
 	for (auto &it : fileSystems) {
 		if (it.prefix == prefix) {
diff --git a/Core/FileSystems/MetaFileSystem.h b/Core/FileSystems/MetaFileSystem.h
index bd18bfaf22..a735106f68 100644
--- a/Core/FileSystems/MetaFileSystem.h
+++ b/Core/FileSystems/MetaFileSystem.h
@@ -57,12 +57,12 @@ public:
 		Reset();
 	}
 
-	void Mount(std::string prefix, std::shared_ptr<IFileSystem> system);
+	void Mount(const std::string &prefix, std::shared_ptr<IFileSystem> system);
 	// Fails if there's not already a file system at prefix.
-	bool Remount(std::string prefix, std::shared_ptr<IFileSystem> system);
+	bool Remount(const std::string &prefix, std::shared_ptr<IFileSystem> system);
 
 	void UnmountAll();
-	void Unmount(std::string prefix);
+	void Unmount(const std::string &prefix);
 
 	// The pointer returned from these are for temporary usage only. Do not store.
 	IFileSystem *GetSystem(const std::string &prefix);
diff --git a/Core/HLE/proAdhoc.cpp b/Core/HLE/proAdhoc.cpp
index 9a1cfc94bd..32ad2b4bfb 100644
--- a/Core/HLE/proAdhoc.cpp
+++ b/Core/HLE/proAdhoc.cpp
@@ -1310,7 +1310,7 @@ void timeoutFriendsRecursive(SceNetAdhocctlPeerInfo * node, int32_t* count) {
 	if (count != NULL) (*count)++;
 }
 
-void sendChat(std::string chatString) {
+void sendChat(const std::string &chatString) {
 	SceNetAdhocctlChatPacketC2S chat;
 	auto n = GetI18NCategory(I18NCat::NETWORKING);
 	chat.base.opcode = OPCODE_CHAT;
diff --git a/Core/HLE/proAdhoc.h b/Core/HLE/proAdhoc.h
index bb80a10a64..49ab5c8e48 100644
--- a/Core/HLE/proAdhoc.h
+++ b/Core/HLE/proAdhoc.h
@@ -1038,7 +1038,7 @@ void addFriend(SceNetAdhocctlConnectPacketS2C * packet);
 * Send chat or get that
 * @param std::string ChatString 
 */
-void sendChat(std::string chatString);
+void sendChat(const std::string &chatString);
 std::vector<std::string> getChatLog();
 int GetChatChangeID();
 int GetChatMessageCount();
diff --git a/Core/HLE/sceKernelMsgPipe.cpp b/Core/HLE/sceKernelMsgPipe.cpp
index 5b44e57bb4..5292d90c10 100644
--- a/Core/HLE/sceKernelMsgPipe.cpp
+++ b/Core/HLE/sceKernelMsgPipe.cpp
@@ -125,7 +125,7 @@ struct MsgPipeWaitingThread
 	}
 };
 
-static bool __KernelMsgPipeThreadSortPriority(MsgPipeWaitingThread thread1, MsgPipeWaitingThread thread2)
+static bool __KernelMsgPipeThreadSortPriority(const MsgPipeWaitingThread &thread1, const MsgPipeWaitingThread &thread2)
 {
 	return __KernelThreadSortPriority(thread1.threadID, thread2.threadID);
 }
diff --git a/Core/HLE/sceNetAdhoc.cpp b/Core/HLE/sceNetAdhoc.cpp
index 14bca68380..00b624a67b 100644
--- a/Core/HLE/sceNetAdhoc.cpp
+++ b/Core/HLE/sceNetAdhoc.cpp
@@ -1233,7 +1233,7 @@ void __UpdateAdhocctlHandlers(u32 flag, u32 error) {
 	adhocctlEvents.push_back({ flag, error });
 }
 
-void __UpdateMatchingHandler(MatchingArgs ArgsPtr) {
+void __UpdateMatchingHandler(const MatchingArgs &ArgsPtr) {
 	std::lock_guard<std::recursive_mutex> adhocGuard(adhocEvtMtx);
 	matchingEvents.push_back(ArgsPtr);
 }
diff --git a/Core/HLE/sceNetAdhoc.h b/Core/HLE/sceNetAdhoc.h
index e2f53efaf6..db9bec3b33 100644
--- a/Core/HLE/sceNetAdhoc.h
+++ b/Core/HLE/sceNetAdhoc.h
@@ -102,7 +102,7 @@ void __NetAdhocInit();
 void __NetAdhocShutdown();
 void __NetAdhocDoState(PointerWrap &p);
 void __UpdateAdhocctlHandlers(u32 flags, u32 error);
-void __UpdateMatchingHandler(MatchingArgs params);
+void __UpdateMatchingHandler(const MatchingArgs &params);
 
 // I have to call this from netdialog
 int sceNetAdhocctlGetState(u32 ptrToStatus);
diff --git a/Core/HW/AsyncIOManager.cpp b/Core/HW/AsyncIOManager.cpp
index 8718bcbdb0..2156d5261a 100644
--- a/Core/HW/AsyncIOManager.cpp
+++ b/Core/HW/AsyncIOManager.cpp
@@ -39,7 +39,7 @@ bool AsyncIOManager::HasOperation(u32 handle) {
 	return false;
 }
 
-void AsyncIOManager::ScheduleOperation(AsyncIOEvent ev) {
+void AsyncIOManager::ScheduleOperation(const AsyncIOEvent &ev) {
 	{
 		std::lock_guard<std::mutex> guard(resultsLock_);
 		if (!resultsPending_.insert(ev.handle).second) {
@@ -143,7 +143,7 @@ void AsyncIOManager::Write(u32 handle, const u8 *buf, size_t bytes) {
 	EventResult(handle, AsyncIOResult(result, usec));
 }
 
-void AsyncIOManager::EventResult(u32 handle, AsyncIOResult result) {
+void AsyncIOManager::EventResult(u32 handle, const AsyncIOResult &result) {
 	std::lock_guard<std::mutex> guard(resultsLock_);
 	if (results_.find(handle) != results_.end()) {
 		ERROR_LOG_REPORT(SCEIO, "Overwriting previous result for file action on handle %d", handle);
diff --git a/Core/HW/AsyncIOManager.h b/Core/HW/AsyncIOManager.h
index 1145db17ac..54d24eb047 100644
--- a/Core/HW/AsyncIOManager.h
+++ b/Core/HW/AsyncIOManager.h
@@ -83,7 +83,7 @@ public:
 	void DoState(PointerWrap &p);
 
 	bool HasOperation(u32 handle);
-	void ScheduleOperation(AsyncIOEvent ev);
+	void ScheduleOperation(const AsyncIOEvent &ev);
 	void Shutdown();
 
 	bool HasResult(u32 handle);
@@ -102,7 +102,7 @@ private:
 	void Read(u32 handle, u8 *buf, size_t bytes, u32 invalidateAddr);
 	void Write(u32 handle, const u8 *buf, size_t bytes);
 
-	void EventResult(u32 handle, AsyncIOResult result);
+	void EventResult(u32 handle, const AsyncIOResult &result);
 
 	std::mutex resultsLock_;
 	std::condition_variable resultsWait_;
diff --git a/Core/KeyMap.cpp b/Core/KeyMap.cpp
index f408182e59..e3a746841d 100644
--- a/Core/KeyMap.cpp
+++ b/Core/KeyMap.cpp
@@ -608,7 +608,7 @@ bool IsKeyMapped(InputDeviceID device, int key) {
 	return false;
 }
 
-bool ReplaceSingleKeyMapping(int btn, int index, MultiInputMapping key) {
+bool ReplaceSingleKeyMapping(int btn, int index, const MultiInputMapping &key) {
 	std::lock_guard<std::recursive_mutex> guard(g_controllerMapLock);
 	// Check for duplicate
 	for (int i = 0; i < (int)g_controllerMap[btn].size(); ++i) {
diff --git a/Core/KeyMap.h b/Core/KeyMap.h
index 976ed67e06..69a9bd40b9 100644
--- a/Core/KeyMap.h
+++ b/Core/KeyMap.h
@@ -188,7 +188,7 @@ namespace KeyMap {
 	// Any configuration will be saved to the Core config.
 	void SetInputMapping(int psp_key, const MultiInputMapping &key, bool replace);
 	// Return false if bind was a duplicate and got removed
-	bool ReplaceSingleKeyMapping(int btn, int index, MultiInputMapping key);
+	bool ReplaceSingleKeyMapping(int btn, int index, const MultiInputMapping &key);
 
 	MappedAnalogAxes MappedAxesForDevice(InputDeviceID deviceId);
 
diff --git a/Core/Loaders.cpp b/Core/Loaders.cpp
index 6bb5f5d343..b304af72bd 100644
--- a/Core/Loaders.cpp
+++ b/Core/Loaders.cpp
@@ -37,7 +37,7 @@
 
 static std::map<std::string, std::unique_ptr<FileLoaderFactory>> factories;
 
-void RegisterFileLoaderFactory(std::string prefix, std::unique_ptr<FileLoaderFactory> factory) {
+void RegisterFileLoaderFactory(const std::string &prefix, std::unique_ptr<FileLoaderFactory> factory) {
 	factories[prefix] = std::move(factory);
 }
 
diff --git a/Core/Loaders.h b/Core/Loaders.h
index 5bc90d3e2c..3eeb301fc3 100644
--- a/Core/Loaders.h
+++ b/Core/Loaders.h
@@ -152,7 +152,7 @@ public:
 	virtual ~FileLoaderFactory() {}
 	virtual FileLoader *ConstructFileLoader(const Path &filename) = 0;
 };
-void RegisterFileLoaderFactory(std::string prefix, std::unique_ptr<FileLoaderFactory> factory);
+void RegisterFileLoaderFactory(const std::string &prefix, std::unique_ptr<FileLoaderFactory> factory);
 
 // Can modify the string filename, as it calls IdentifyFile above.
 bool LoadFile(FileLoader **fileLoaderPtr, std::string *error_string);
diff --git a/Core/Reporting.cpp b/Core/Reporting.cpp
index 6d1f5a983c..3f4d8df28d 100644
--- a/Core/Reporting.cpp
+++ b/Core/Reporting.cpp
@@ -623,7 +623,7 @@ namespace Reporting
 		return true;
 	}
 
-	bool Enable(bool flag, std::string host)
+	bool Enable(bool flag, const std::string &host)
 	{
 		if (IsSupported() && IsEnabled() != flag)
 		{
diff --git a/Core/Reporting.h b/Core/Reporting.h
index 1d254256f7..fff45d3b15 100644
--- a/Core/Reporting.h
+++ b/Core/Reporting.h
@@ -53,7 +53,7 @@ namespace Reporting
 
 	// Set the current enabled state of the reporting system and desired reporting server host.
 	// Returns if anything was changed.
-	bool Enable(bool flag, std::string host);
+	bool Enable(bool flag, const std::string &host);
 
 	// Use the default reporting setting (per compiled settings) of host and enabled state.
 	void EnableDefault();
diff --git a/Core/SaveState.cpp b/Core/SaveState.cpp
index 1b0087444f..80563be08d 100644
--- a/Core/SaveState.cpp
+++ b/Core/SaveState.cpp
@@ -397,7 +397,7 @@ namespace SaveState
 		pspFileSystem.DoState(p);
 	}
 
-	void Enqueue(SaveState::Operation op)
+	void Enqueue(const SaveState::Operation &op)
 	{
 		if (Achievements::HardcoreModeActive()) {
 			if (g_Config.bAchievementsSaveStateInHardcoreMode && ((op.type == SaveState::SAVESTATE_SAVE) || (op.type == SAVESTATE_SAVE_SCREENSHOT))) {
diff --git a/Core/Util/GameManager.cpp b/Core/Util/GameManager.cpp
index 52bc6a6821..17aa0013cd 100644
--- a/Core/Util/GameManager.cpp
+++ b/Core/Util/GameManager.cpp
@@ -86,12 +86,12 @@ Path GameManager::GetTempFilename() const {
 #endif
 }
 
-bool GameManager::IsGameInstalled(std::string name) {
+bool GameManager::IsGameInstalled(const std::string &name) {
 	Path pspGame = GetSysDirectory(DIRECTORY_GAME);
 	return File::Exists(pspGame / name);
 }
 
-bool GameManager::DownloadAndInstall(std::string storeFileUrl) {
+bool GameManager::DownloadAndInstall(const std::string &storeFileUrl) {
 	if (curDownload_.get() != nullptr) {
 		ERROR_LOG(HLE, "Can only process one download at a time");
 		return false;
@@ -107,7 +107,7 @@ bool GameManager::DownloadAndInstall(std::string storeFileUrl) {
 	return true;
 }
 
-bool GameManager::IsDownloading(std::string storeZipUrl) {
+bool GameManager::IsDownloading(const std::string &storeZipUrl) {
 	if (curDownload_)
 		return curDownload_->url() == storeZipUrl;
 	return false;
@@ -128,7 +128,7 @@ float GameManager::DownloadSpeedKBps() {
 	return 0.0f;
 }
 
-void GameManager::UninstallGame(std::string name) {
+void GameManager::UninstallGame(const std::string &name) {
 	SetCurrentThreadName("UninstallGame");
 
 	AndroidJNIThreadContext context;  // Destructor detaches.
@@ -285,7 +285,7 @@ ZipFileContents DetectZipFileContents(struct zip *z, ZipFileInfo *info) {
 }
 
 // Parameters need to be by value, since this is a thread func.
-bool GameManager::InstallGame(Path url, Path fileName, bool deleteAfter) {
+bool GameManager::InstallGame(const Path &url, const Path &fileName, bool deleteAfter) {
 	SetCurrentThreadName("InstallGame");
 
 	if (installDonePending_) {
diff --git a/Core/Util/GameManager.h b/Core/Util/GameManager.h
index 0d6b9ce78e..ec4ad5b8c2 100644
--- a/Core/Util/GameManager.h
+++ b/Core/Util/GameManager.h
@@ -42,11 +42,11 @@ class GameManager {
 public:
 	GameManager();
 
-	bool IsGameInstalled(std::string name);
+	bool IsGameInstalled(const std::string &name);
 
 	// This starts off a background process.
-	bool DownloadAndInstall(std::string storeZipUrl);
-	bool IsDownloading(std::string storeZipUrl);
+	bool DownloadAndInstall(const std::string &storeZipUrl);
+	bool IsDownloading(const std::string &storeZipUrl);
 
 	// Cancels the download in progress, if any.
 	bool CancelDownload();
@@ -79,12 +79,12 @@ public:
 
 private:
 	// TODO: The return value on this is a bit pointless, we can't get at it.
-	bool InstallGame(Path url, Path tempFileName, bool deleteAfter);
+	bool InstallGame(const Path &url, const Path &tempFileName, bool deleteAfter);
 	bool InstallMemstickGame(struct zip *z, const Path &zipFile, const Path &dest, const ZipFileInfo &info, bool allowRoot, bool deleteAfter);
 	bool InstallMemstickZip(struct zip *z, const Path &zipFile, const Path &dest, const ZipFileInfo &info, bool deleteAfter);
 	bool InstallZippedISO(struct zip *z, int isoFileIndex, const Path &zipfile, bool deleteAfter);
 	bool InstallRawISO(const Path &zipFile, const std::string &originalName, bool deleteAfter);
-	void UninstallGame(std::string name);
+	void UninstallGame(const std::string &name);
 
 	void InstallDone();
 
diff --git a/Core/Util/PPGeDraw.cpp b/Core/Util/PPGeDraw.cpp
index 8a4f3f90f0..6c88b29a37 100644
--- a/Core/Util/PPGeDraw.cpp
+++ b/Core/Util/PPGeDraw.cpp
@@ -948,7 +948,7 @@ static PPGeTextDrawerImage PPGeGetTextImage(const char *text, const PPGeStyle &s
 	return im;
 }
 
-static void PPGeDrawTextImage(PPGeTextDrawerImage im, float x, float y, const PPGeStyle &style) {
+static void PPGeDrawTextImage(const PPGeTextDrawerImage &im, float x, float y, const PPGeStyle &style) {
 	if (!im.ptr) {
 		return;
 	}