sys_fs: Optimize concurrent file reads

rpcs3/Emu/Cell/Modules/cellSaveData.cpp

@@ -1854,17 +1854,17 @@ static NEVER_INLINE error_code savedata_op(ppu_thread& ppu, u32 operation, u32 v
 			}
 
 			const auto file = std::as_const(all_files).find(file_path);
+			const u64 pos = fileSet->fileOffset;
 
-			if (file == all_files.cend() || file->second.size() <= fileSet->fileOffset)
+			if (file == all_files.cend() || file->second.size() <= pos)
 			{
 				cellSaveData.error("Failed to open file %s%s (size=%d, fileOffset=%d)", dir_path, file_path, file == all_files.cend() ? -1 : file->second.size(), fileSet->fileOffset);
 				savedata_result = CELL_SAVEDATA_ERROR_FAILURE;
 				break;
 			}
 
 			// Read from memory file to vm
-			file->second.seek(fileSet->fileOffset);
-			const u64 rr = lv2_file::op_read(file->second, fileSet->fileBuf, fileSet->fileSize);
+			const u64 rr = lv2_file::op_read(file->second, fileSet->fileBuf, fileSet->fileSize, pos);
 			fileGet->excSize = ::narrow<u32>(rr);
 			break;
 		}

rpcs3/Emu/Cell/lv2/sys_fs.cpp

@@ -16,6 +16,7 @@
 
 #include <filesystem>
 #include <span>
+#include <shared_mutex>
 
 LOG_CHANNEL(sys_fs);
 
@@ -371,7 +372,7 @@ lv2_fs_object::lv2_fs_object(utils::serial& ar, bool)
 {
 }
 
-u64 lv2_file::op_read(const fs::file& file, vm::ptr<void> buf, u64 size)
+u64 lv2_file::op_read(const fs::file& file, vm::ptr<void> buf, u64 size, u64 opt_pos)
 {
 	// Copy data from intermediate buffer (avoid passing vm pointer to a native API)
 	std::vector<uchar> local_buf(std::min<u64>(size, 65536));
@@ -381,7 +382,7 @@ u64 lv2_file::op_read(const fs::file& file, vm::ptr<void> buf, u64 size)
 	while (result < size)
 	{
 		const u64 block = std::min<u64>(size - result, local_buf.size());
-		const u64 nread = file.read(+local_buf.data(), block);
+		const u64 nread = (opt_pos == umax ? file.read(local_buf.data(), block) : file.read_at(opt_pos + result, local_buf.data(), block));
 
 		std::memcpy(static_cast<uchar*>(buf.get_ptr()) + result, local_buf.data(), nread);
 		result += nread;
@@ -1930,7 +1931,19 @@ error_code sys_fs_fcntl(ppu_thread& ppu, u32 fd, u32 op, vm::ptr<void> _arg, u32
 			sys_fs.error("%s type: Writing %u bytes to FD=%d (path=%s)", file->type, arg->size, file->name.data());
 		}
 
-		std::lock_guard lock(file->mp->mutex);
+		std::unique_lock wlock(file->mp->mutex, std::defer_lock);
+		std::shared_lock rlock(file->mp->mutex, std::defer_lock);
+
+		if (op == 0x8000000b)
+		{
+			// Writer lock
+			wlock.lock();
+		}
+		else
+		{
+			// Reader lock (not needing exclusivity in this special case because the state should not change)
+			rlock.lock();
+		}
 
 		if (!file->file)
 		{
@@ -1947,14 +1960,23 @@ error_code sys_fs_fcntl(ppu_thread& ppu, u32 fd, u32 op, vm::ptr<void> _arg, u32
 			return CELL_EBUSY;
 		}
 
-		const u64 old_pos = file->file.pos();
-		file->file.seek(arg->offset);
+		u64 old_pos = umax;
+		const u64 op_pos = arg->offset;
+
+		if (op == 0x8000000b)
+		{
+			old_pos = file->file.pos();
+			file->file.seek(op_pos);
+		}
 
 		arg->out_size = op == 0x8000000a
-			? file->op_read(arg->buf, arg->size)
+			? file->op_read(arg->buf, arg->size, op_pos)
 			: file->op_write(arg->buf, arg->size);
 
-		ensure(old_pos == file->file.seek(old_pos));
+		if (op == 0x8000000b)
+		{
+			ensure(old_pos == file->file.seek(old_pos));
+		}
 
 		// TODO: EDATA corruption detection
 

rpcs3/Emu/Cell/lv2/sys_fs.h

@@ -157,7 +157,7 @@ struct lv2_fs_mount_point
 	const bs_t<lv2_mp_flag> flags{};
 	lv2_fs_mount_point* const next = nullptr;
 
-	mutable std::recursive_mutex mutex;
+	mutable shared_mutex mutex;
 };
 
 extern lv2_fs_mount_point g_mp_sys_dev_hdd0;
@@ -340,11 +340,11 @@ struct lv2_file final : lv2_fs_object
 	static open_result_t open(std::string_view vpath, s32 flags, s32 mode, const void* arg = {}, u64 size = 0);
 
 	// File reading with intermediate buffer
-	static u64 op_read(const fs::file& file, vm::ptr<void> buf, u64 size);
+	static u64 op_read(const fs::file& file, vm::ptr<void> buf, u64 size, u64 opt_pos = umax);
 
-	u64 op_read(vm::ptr<void> buf, u64 size) const
+	u64 op_read(vm::ptr<void> buf, u64 size, u64 opt_pos = umax) const
 	{
-		return op_read(file, buf, size);
+		return op_read(file, buf, size, opt_pos);
 	}
 
 	// File writing with intermediate buffer