On Tue, Aug 30, 2022 at 05:38:35PM +0800, Ming Lei wrote:
> 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 think where I'm confused is where is pthread_create called to create
this thread? (Or maybe this is being called on an io_uring thread context?)
> > 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.
nbd_poll -> poll(2) -> POLLIN. The state machine code (lib/states.c)
will call recv(2) and may complete zero, one or several NBD commands
before it blocks again.
Rich.
--
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