On Tue, Aug 30, 2022 at 11:51:00AM +0100, Richard W.M. Jones wrote:
> 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?)
My patch does not change where/how nbd work thread is created, and is
still created in start_daemon() as you did.
>
> > > 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.
OK, my patch works pretty well with this way.
Thanks,
Ming
_______________________________________________
Libguestfs mailing list
Libguestfs@redhat.com
https://listman.redhat.com/mailman/listinfo/libguestfs
