我正在尝试整数方式解析二进制文件以检查整数值是否满足某个条件,但循环非常缓慢。
此外,我发现内存映射文件
是将文件快速读入内存的最快方法,因此我正在使用以下基于Boost
的代码:
unsigned long long int get_file_size(const char *file_path) {
const filesystem::path file{file_path};
const auto generic_path = file.generic_path();
return filesystem::file_size(generic_path);
}
boost::iostreams::mapped_file_source read_bytes(const char *file_path,
const unsigned long long int offset,
const unsigned long long int length) {
boost::iostreams::mapped_file_params parameters;
parameters.path = file_path;
parameters.length = static_cast<size_t>(length);
parameters.flags = boost::iostreams::mapped_file::mapmode::readonly;
parameters.offset = static_cast<boost::iostreams::stream_offset>(offset);
boost::iostreams::mapped_file_source file;
file.open(parameters);
return file;
}
boost::iostreams::mapped_file_source read_bytes(const char *file_path) {
const auto file_size = get_file_size(file_path);
const auto mapped_file_source = read_bytes(file_path, 0, file_size);
return mapped_file_source;
}
我的测试用例大致如下:
inline auto test_parsing_binary_file_performance() {
const auto start_time = get_time();
const std::filesystem::path input_file_path = "...";
const auto mapped_file_source = read_bytes(input_file_path.string().c_str());
const auto file_buffer = mapped_file_source.data();
const auto file_buffer_size = mapped_file_source.size();
LOG_S(INFO) << "File buffer size: " << file_buffer_size;
auto printed_lap = (long) (file_buffer_size / (double) 1000);
printed_lap = round_to_nearest_multiple(printed_lap, sizeof(int));
LOG_S(INFO) << "Printed lap: " << printed_lap;
std::vector<int> values;
values.reserve(file_buffer_size / sizeof(int)); // Pre-allocate a large enough vector
// Iterate over every integer
for (auto file_buffer_index = 0; file_buffer_index < file_buffer_size; file_buffer_index += sizeof(int)) {
const auto value = *(int *) &file_buffer[file_buffer_index];
if (value >= 0x30000000 && value < 0x49000000 - sizeof(int) + 1) {
values.push_back(value);
}
if (file_buffer_index % printed_lap == 0) {
LOG_S(INFO) << std::setprecision(4) << file_buffer_index / (double) file_buffer_size * 100 << "%";
}
}
LOG_S(INFO) << "Values found count: " << values.size();
print_time_taken(start_time, false, "Parsing binary file");
}
内存映射文件
的读取速度如预期般快,但在我的设备上逐个整数地迭代速度过慢,尽管硬件条件良好(SSD
等)。2020-12-20 13:04:35.124 ( 0.019s) [main thread ]Tests.hpp:387 INFO| File buffer size: 419430400
2020-12-20 13:04:35.124 ( 0.019s) [main thread ]Tests.hpp:390 INFO| Printed lap: 419432
2020-12-20 13:04:35.135 ( 0.029s) [main thread ]Tests.hpp:405 INFO| 0%
2020-12-20 13:04:35.171 ( 0.065s) [main thread ]Tests.hpp:405 INFO| 0.1%
2020-12-20 13:04:35.196 ( 0.091s) [main thread ]Tests.hpp:405 INFO| 0.2%
2020-12-20 13:04:35.216 ( 0.111s) [main thread ]Tests.hpp:405 INFO| 0.3%
2020-12-20 13:04:35.241 ( 0.136s) [main thread ]Tests.hpp:405 INFO| 0.4%
2020-12-20 13:04:35.272 ( 0.167s) [main thread ]Tests.hpp:405 INFO| 0.5%
2020-12-20 13:04:35.293 ( 0.188s) [main thread ]Tests.hpp:405 INFO| 0.6%
2020-12-20 13:04:35.314 ( 0.209s) [main thread ]Tests.hpp:405 INFO| 0.7%
2020-12-20 13:04:35.343 ( 0.237s) [main thread ]Tests.hpp:405 INFO| 0.8%
2020-12-20 13:04:35.366 ( 0.261s) [main thread ]Tests.hpp:405 INFO| 0.9%
2020-12-20 13:04:35.399 ( 0.293s) [main thread ]Tests.hpp:405 INFO| 1%
2020-12-20 13:04:35.421 ( 0.315s) [main thread ]Tests.hpp:405 INFO| 1.1%
2020-12-20 13:04:35.447 ( 0.341s) [main thread ]Tests.hpp:405 INFO| 1.2%
2020-12-20 13:04:35.468 ( 0.362s) [main thread ]Tests.hpp:405 INFO| 1.3%
2020-12-20 13:04:35.487 ( 0.382s) [main thread ]Tests.hpp:405 INFO| 1.4%
2020-12-20 13:04:35.520 ( 0.414s) [main thread ]Tests.hpp:405 INFO| 1.5%
2020-12-20 13:04:35.540 ( 0.435s) [main thread ]Tests.hpp:405 INFO| 1.6%
2020-12-20 13:04:35.564 ( 0.458s) [main thread ]Tests.hpp:405 INFO| 1.7%
2020-12-20 13:04:35.586 ( 0.480s) [main thread ]Tests.hpp:405 INFO| 1.8%
2020-12-20 13:04:35.608 ( 0.503s) [main thread ]Tests.hpp:405 INFO| 1.9%
2020-12-20 13:04:35.636 ( 0.531s) [main thread ]Tests.hpp:405 INFO| 2%
2020-12-20 13:04:35.658 ( 0.552s) [main thread ]Tests.hpp:405 INFO| 2.1%
2020-12-20 13:04:35.679 ( 0.574s) [main thread ]Tests.hpp:405 INFO| 2.2%
2020-12-20 13:04:35.702 ( 0.597s) [main thread ]Tests.hpp:405 INFO| 2.3%
2020-12-20 13:04:35.727 ( 0.622s) [main thread ]Tests.hpp:405 INFO| 2.4%
2020-12-20 13:04:35.769 ( 0.664s) [main thread ]Tests.hpp:405 INFO| 2.5%
2020-12-20 13:04:35.802 ( 0.697s) [main thread ]Tests.hpp:405 INFO| 2.6%
2020-12-20 13:04:35.831 ( 0.726s) [main thread ]Tests.hpp:405 INFO| 2.7%
2020-12-20 13:04:35.860 ( 0.754s) [main thread ]Tests.hpp:405 INFO| 2.8%
2020-12-20 13:04:35.887 ( 0.781s) [main thread ]Tests.hpp:405 INFO| 2.9%
2020-12-20 13:04:35.924 ( 0.818s) [main thread ]Tests.hpp:405 INFO| 3%
2020-12-20 13:04:35.956 ( 0.850s) [main thread ]Tests.hpp:405 INFO| 3.1%
2020-12-20 13:04:35.998 ( 0.893s) [main thread ]Tests.hpp:405 INFO| 3.2%
2020-12-20 13:04:36.033 ( 0.928s) [main thread ]Tests.hpp:405 INFO| 3.3%
2020-12-20 13:04:36.060 ( 0.955s) [main thread ]Tests.hpp:405 INFO| 3.4%
2020-12-20 13:04:36.102 ( 0.997s) [main thread ]Tests.hpp:405 INFO| 3.5%
2020-12-20 13:04:36.132 ( 1.026s) [main thread ]Tests.hpp:405 INFO| 3.6%
...
2020-12-20 13:05:03.456 ( 28.351s) [main thread ]Tests.hpp:410 INFO| Values found count: 10650389
2020-12-20 13:05:03.456 ( 28.351s) [main thread ] benchmark.cpp:31 INFO| Parsing binary file took 28.341 second(s)
解析那些“419 MB”的数据通常需要大约28-70秒,即使在“Release”模式下编译也没有真正帮助。是否有任何方法可以缩短这段时间?看起来我执行的操作不应该如此低效。请注意,我正在使用“GCC 10”为“Linux 64位”编译。根据评论建议,使用具有“advise()”的“内存映射文件”也不能提高性能。
boost::interprocess::file_mapping file_mapping(input_file_path.string().data(), boost::interprocess::read_only);
boost::interprocess::mapped_region mapped_region(file_mapping, boost::interprocess::read_only);
mapped_region.advise(boost::interprocess::mapped_region::advice_sequential);
const auto file_buffer = (char *) mapped_region.get_address();
const auto file_buffer_size = mapped_region.get_size();
...
根据评论和答案得出的一些结论:
- 使用
advise(boost::interprocess::mapped_region::advice_sequential)
没有帮助 - 不调用
reserve()
或者调用时大小刚好为正确值,可以将性能提高一倍 - 直接迭代
int *
比迭代char *
稍慢一些 - 使用
std::vector
收集结果比使用std::set
稍快一些 - 性能对于进度日志记录来说微不足道
*(int *)
是UB(严格别名违规)。还有%
的日志行在哪里?请包含前几个。添加file.advise(boost::interprocess::mapped_region::advice_sequential);
会有帮助吗? - rustyxadvise()
的memory-mapped file
方法,但它并没有提高性能。此外,我添加了一些缺失的日志行。 - BullyWiiPlaza4 秒
,谢谢您指出内存映射文件
会导致多次磁盘访问的提示。我用将整个文件读入内存后再处理它的方式替换了那段代码,这解决了性能问题,大大缩短了处理时间。 - BullyWiiPlaza