Re: [Libguestfs] [PATCH libnbd] ublk: Add new nbdublk program

nbd work thread is created by nbd target code just like before, but the thread is changed to the following way, basically bound with one aio_ctx:

while (!ublksrv_aio_ctx_dead(aio_ctx)) { struct aio_list compl; aio_list_init(&compl); //retrieve requests from submit list, and submit each one via //aio_submitter(), if anyone is done, add it to &compl. ublksrv_aio_submit_worker(aio_ctx, aio_submitter, &compl); //add requests completed from command_completed() to &compl pthread_spin_lock(&c->lock); aio_list_splice(&c->list, &compl); pthread_spin_unlock(&c->lock); //notify io_uring thread for the completed requests in &compl, //then batching complete & re-issue can be done in io_uring //context ublksrv_aio_complete_worker(aio_ctx, &compl); //wait for network IO and evevfd from io_uring at the same time //so if either one is ready, nbd_poll2() will return from sleep if (nbd_poll2 (h, aio_ctx->efd, -1) == -1) { fprintf (stderr, "%s\n", nbd_get_error ()); exit (EXIT_FAILURE); } }

> I've never used eventfd before and the man page for it is very opaque. > > > In your previous implementation, nbd work thread may wait on one pthread > > mutex and aio_poll(), this way may not be efficient, given when waiting > > on one event, another events can't be handled. > > I'm not sure what "event" means in this context. Does it mean > "NBD command"? Or poll(2) event? Here event is generic, I meant: NBD IO ready(exactly what aio_poll() waits for) or io_uring eventfd ready(one write done from nbd_handle_io_async()). > > There are multiple (usually 4) nbd_work threads, one for each NBD > network connection. Each NBD network connection can handle many > commands in flight at once. OK, but aio_poll() supposes to get notified if one command is done, so here it is just the implementation detail, but correct me if I am wrong.