On Sat, May 31, 2014 at 08:43:07PM +0200, Max Reitz wrote: > For the NBD server to work with dataplane, it needs to correctly access > the exported BDS. It makes the most sense to run both in the same > AioContext, therefore this series implements methods for tracking a > BDS's AioContext and makes NBD make use of this for keeping the clients > connected to that BDS in the same AioContext. > > The reason this is an RFC and not a PATCH is my inexperience with AIO, > coroutines and the like. Also, I'm not sure about what to do about the > coroutines. The NBD server has up to two coroutines per client: One for > receiving and one for sending. Theoretically, both have to be > "transferred" to the new AioContext if it is changed; however, as far as > I see it, coroutines are not really bound to an AioContext, they are > simply run in the AioContext entering them. Therefore, I think a > transfer is unnecessary. All coroutines are entered from nbd_read() and > nbd_restart_write(), both of which are AIO routines registered via > aio_set_fd_handler2(). > > As bs_aio_detach() unregisters all of these routines, the coroutines can > no longer be entered, but only after bs_aio_attach() is called again. > Then, when they are called, they will enter the coroutines in the new > AioContext. Therefore, I think an explicit transfer unnecessary. > > However, if bs_aio_detach() is called from a different thread than the > old AioContext is running in, we may still have coroutines running for > which we should wait before returning from bs_aio_detach(). > > But because of my inexperience with coroutines, I'm not sure. I now have > these patches nearly unchanged here for about a week and I'm looking for > ways of testing them, but so far I could only test whether the old use > cases work, but not whether they will work for what they are intended to > do: With BDS changing their AioContext. > > So, because I'm not sure what else to do and because I don't know how to > test multiple AIO threads (how do I move a BDS into another iothread?) > I'm just sending this out as an RFC. > > > Max Reitz (5): > nbd: Correct name comparison for export_set_name() > aio: Add io_read_poll() callback > nbd: Use aio_set_fd_handler2() > block: Add AIO followers > nbd: Follow the BDS' AIO context > > aio-posix.c | 26 ++++++++++++++++----- > block.c | 55 +++++++++++++++++++++++++++++++++++++++++++ > include/block/aio.h | 12 ++++++++++ > include/block/block_int.h | 40 ++++++++++++++++++++++++++++++++ > include/qemu/main-loop.h | 1 - > nbd.c | 59 > ++++++++++++++++++++++++++++++++++++++--------- > 6 files changed, 175 insertions(+), 18 deletions(-)
Thanks for the RFC. It looks like the concept will work correctly. I left comments, a lot of them are just ideas and you don't have to implement them if you don't want to. Stefan