本文主要介绍fio是如何运行的，并且以单线程、单job为例
fio的入口在fio.c中的main函数,下面列出了main函数，此处只出示了一些调用的关键函数
int main(int argc, char *argv[], char *envp[])
{
parse_options(argc, argv);
fio_backend();
}
在main函数中主要调用了两个关键函数，parse_options，顾名思义，就是分析options，也就是fio的参数，而fio_backend()函数则是fio进程的入口
fio_backend()函数在backend.c文件中
int fio_backend(void)
{
......
run_threads();
......
}
在fio_backend()函数中，初始化一些数据结构之后，调用了run_threads()(backend.c)函数，该函数是fio用来创建譬如I/O, verify线程等。
/*
* Main function for kicking off and reaping jobs, as needed.
*/
static void run_threads(void)
{
......
todo = thread_number;
......
while (todo) {
if (td->o.use_thread) {
......
ret = pthread_create(&td->thread, NULL,thread_main, td);
ret = pthread_detach(td->thread);
......
}
......
}
在这个函数中，创建了thread_main线程(backend.c)，这个线程功能是，生成I/O，发送并完成I/O，记录数据等。
/*
* Entry point for the thread based jobs. The process based jobs end up
* here as well, after a little setup.
*/
static void *thread_main(void *data)
{
........
/*
* May alter parameters that init_io_u() will use, so we need to
* do this first.
* 下面两个函数的主要功能是生成读写的参数，offset，len
*/
if (init_iolog(td))
goto err; if (init_io_u(td))
goto err;
......
while (keep_running(td)) {
do_io(td);
do_verify(td, verify_bytes);//如果需要verification的话
}
}
如果不考虑verify的话，下面主要看do_io(backend.c)函数。
/*
* Main IO worker function. It retrieves io_u's to process and queues
* and reaps them, checking for rate and errors along the way.
*
* Returns number of bytes written and trimmed.
*/
static uint64_t do_io(struct thread_data *td)
{
......
//下面是do_io的主循环，判断条件是，io_log里有生成的pos信息，而且已经iuuse的数据小于总数据，
while ((td->o.read_iolog_file && !flist_empty(&td->io_log_list)) ||
(!flist_empty(&td->trim_list)) || !io_bytes_exceeded(td) ||
td->o.time_based) {
......
io_u = get_io_u(td);// io_u,是一个io unit，是根据参数生成的io unit
......
ret = td_io_queue(td, io_u); //将io_u提交到队列中
switch (ret) {
case FIO_Q_COMPLETED: //处理错误，以及同步的操作
......
case FIO_Q_QUEUED://成功入队
bytes_issued += io_u->xfer_buflen;
case FIO_Q_BUSY: //队伍满了，重新入队
.......
/*
* See if we need to complete some commands. Note that we
* can get BUSY even without IO queued, if the system is
* resource starved.
*/
full = queue_full(td) || (ret == FIO_Q_BUSY && td->cur_depth);
if (full || !td->o.iodepth_batch_complete) {
min_evts = min(td->o.iodepth_batch_complete,td->cur_depth);
/*
* if the queue is full, we MUST reap at least 1 event
*/
if (full && !min_evts)
min_evts = ;
do {
ret = io_u_queued_complete(td, min_evts, bytes_done);
} while (full && (td->cur_depth > td->o.iodepth_low));
}
}
上面do_io函数的关键入队函数td_io_queue(ioengines.c)
int td_io_queue(struct thread_data *td, struct io_u *io_u)
{
......
ret = td->io_ops->queue(td, io_u);
......
else if (ret == FIO_Q_QUEUED) {
int r;
if (ddir_rw(io_u->ddir)) {
td->io_u_queued++;
td->ts.total_io_u[io_u->ddir]++;
}
if (td->io_u_queued >= td->o.iodepth_batch) {
r = td_io_commit(td);
if (r < )
return r;
}
}
}
int td_io_commit(struct thread_data *td)
{
......
int ret;
if (td->io_ops->commit) {
ret = td->io_ops->commit(td);
}
......
return ;
}
对于td->iops，它是在各个engines中定义了，以libaio(/engines/libaio.c)为例，调用的函数就是相应engines里对应的函数
static struct ioengine_ops ioengine = {
.name = "libaio",
.version = FIO_IOOPS_VERSION,
.init = fio_libaio_init,
.prep = fio_libaio_prep,
.queue = fio_libaio_queue,
.commit = fio_libaio_commit,
.cancel = fio_libaio_cancel,
.getevents = fio_libaio_getevents,
.event = fio_libaio_event,
.cleanup = fio_libaio_cleanup,
.open_file = generic_open_file,
.close_file = generic_close_file,
.get_file_size = generic_get_file_size,
.options = options,
.option_struct_size = sizeof(struct libaio_options),
};对于reap流程里的io_u_queued_complete(io_u.c)函数
/*
* Called to complete min_events number of io for the async engines.
*/
int io_u_queued_complete(struct thread_data *td, int min_evts,
uint64_t *bytes)
{
...... ret = td_io_getevents(td, min_evts, td->o.iodepth_batch_complete, tvp);
......
} int td_io_getevents(struct thread_data *td, unsigned int min, unsigned int max,
struct timespec *t)
{
int r = ; if (min > && td->io_ops->commit) {
r = td->io_ops->commit(td);
if (r < )
goto out;
}
if (max > td->cur_depth)
max = td->cur_depth;
if (min > max)
max = min; r = ;
if (max && td->io_ops->getevents)
r = td->io_ops->getevents(td, min, max, t);
out:
......
return r;
}
这里调用的getevents也是各个engines里定义的函数