Hi, On 4 October 2017 at 07:58, Никита Горбунов <tshiva@xxxxxxxxxxx> wrote: > I write my ioengine and have some questions about how work fio. > > 1. What to do if function "getevents" transmitted pointer (const > struct timespec *t) which indicated garbage? > I want to paused my ioengine on some msec(sec,nsec) when ioengine > wants get answer about recording of write. I don't understand how can > get time for waiting if time pointer indicated garbage. Why does he > pass the pointer to the garbage? You need to check if it is not null before you use it. Off the top of my head I think this is the only place I've seen it being used https://github.com/axboe/fio/blob/fio-3.1/engines/libaio.c#L145 and it's only usuable in certain conditions. If you chase your way up the code to https://github.com/axboe/fio/blob/fio-3.1/io_u.c#L2001 you can see you only get a non-NULL timespec when you don't require a minimum number of events before returning (i.e. the case where you're using the libaio ioengine with userspace_reap=1 - see http://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-userspace-reap ). If you need to just wait for an amount of time you can grab/check time with fio_gettime/mtime_since_now as in https://github.com/axboe/fio/blob/fio-3.1/engines/libaio.c#L284 . > 2. What is the call queue function of ioengine? Can you write minimal > viable call chain? (init->open->queue->commit->getevents->cleanup) It's going to depend. The comments in the skeleton ioengine (https://github.com/axboe/fio/blob/fio-3.1/engines/skeleton_external.c actually state which callbacks must be present (e.g. commit is optional because your ioengine might be synchrnous). Even open/close may not be required if the ioengine is somehow synthetic or connectionless. There are also additional optional callbacks that can be added that are not mentioned in the skeleton ioengine... Your suggested chain looks OK if all those are callbacks are defined but you may find queue is called multiple times successively (since it seems your theoretical ioengine is async), getevents may be called multiple times etc. > 3. Are the function of ioengine can be called in several threads > without indicated numjobs? Each numjob gets its own ioengine - you don't know if a job is going to be run as a process or a thread. If your ioengine is using something that's not thread safe then your ioengine is responsible for serializing access to it... > 4. Why in null-ioengine when iodepth=1 we indicate this flag: > "td->io_ops->flags |= FIO_SYNCIO;" (sorry for my english) (I think this setting is informal enough you don't need to worry too much about your English so long as people know what you mean :-) That ioengine "wants" to behave like a synchronous ioengine when the depth is 1 and like an asynchronous ioengine when the depth is greater than 1. I'm guessing wildly but perhaps being an asynchronous ioengine induces a bit of extra overhead? If you're writing a "throw everything away" ioengine that is going as fast as possible for benchmarking the other parts of fio itself, every little counts... -- Sitsofe | http://sucs.org/~sits/ -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
