我正在嘗試Linux libaio以在服務器應用程序中優化IO性能。我相信我已經做了所有必要的事情(使用O_DIRECT,將緩衝區與內存頁面對齊...)。我在等待io_submit立即返回,但一個簡單的測試顯示它實際上需要80微秒左右的時間才能在我的核心i7筆記本電腦上返回。我是否期望過多或者測試計劃有問題? (編譯G ++ --std =的C++ 0x -laio)具有libaio性能問題的Linux異步IO
#include <unistd.h>
#include <fcntl.h>
#include <libaio.h>
#include <errno.h>
#include <cstdlib>
#include <cstdio>
#include <iostream>
#include <chrono>
// Open the file for write, return the file descriptor
int open_write(char const* file)
{
int fd = open(file, O_DIRECT|O_CREAT|O_WRONLY, S_IRWXU|S_IRWXG|S_IROTH);
if (fd < 0) {
perror("open_write");
exit(1);
}
}
// Make a buffer of _size_ byte, fill with 'a', return the buffer, it should be aligned to memory page
void* make_write_buffer(size_t size)
{
void* buf = 0;
int ret = posix_memalign((void**)&buf, sysconf(_SC_PAGESIZE), size);
if (ret < 0 || buf == 0) {
perror("make_write_buffer");
exit(1);
}
memset(buf, 'a', size);
return buf;
}
int main (int argc, char *argv[])
{
static const size_t SIZE = 16 * 1024;
// Prepare file and buffer to write
int write_fd = open_write("test.dat");
void* buf = make_write_buffer(SIZE);
// Prepare aio
io_context_t ctx;
memset(&ctx, 0, sizeof(ctx));
const int maxEvents = 32;
io_setup(maxEvents, &ctx);
iocb *iocbpp = new iocb;
io_prep_pwrite(iocbpp, write_fd, buf, SIZE, 0);
using namespace std::chrono;
// Submit aio task
auto start = monotonic_clock::now();
int status = io_submit(ctx, 1, &iocbpp);
if (status < 0) {
errno = -status;
perror("io_submit");
exit(1);
}
auto dur = duration_cast<microseconds>(monotonic_clock::now() - start);
std::cout << "io_submit takes: " << dur.count() << " microseconds." << std::endl;
io_event events[10];
int n = io_getevents(ctx, 1, 10, events, NULL);
close(write_fd);
io_destroy(ctx);
delete iocbpp;
free(buf);
return 0;
}
80微秒,慢? :p最佳猜想:你的過程已經安排完畢。如果你增加你的緩衝區大小呢? – fge 2011-12-25 13:07:38
另外,測量幾百(或幾千)個調用,對該函數的第一次調用進行計時似乎不是一個好主意。 – Mat 2011-12-25 13:08:37
謝謝,馬特。我做了幾次,80微秒是平均水平。 「冷」操作有時可能需要400微秒。 – 2011-12-25 21:36:25