On 11/09/2015 13:01, Fam Zheng wrote: > On Fri, 09/11 12:46, Paolo Bonzini wrote: >> >> >> On 11/09/2015 12:40, Fam Zheng wrote: >>> On Fri, 09/11 11:54, Paolo Bonzini wrote: >>>> >>>> >>>> On 11/09/2015 11:44, Fam Zheng wrote: >>>>>>>> That would be a step back. Using GSource is useful because it lets >>>>>>>> you integrate libraries such as GTK+. >>>>>>> >>>>>>> Can we move GTK to a separate GSource thread? >>>>>> >>>>>> I think that GTK should always run in the main thread, or at least the >>>>>> one running the default main loop / GMainContext. >>>>> >>>>> Yeah it's basically GMainContext staying in the main thread and >>>>> block/net/chardev I/O put in a new AioContext thread. >>>> >>>> Why? The point of an event loop is that you can multiplex everything on >>>> the same thread. Unless we have specific needs (e.g. scalability) one >>>> thread is the way to go and keep things simple. >>> >>> The reason is scalability. :) >> >> Scalability of what? If virtio-net or virtio-serial needs to be more >> scalable, putting all of them into a non-main-loop thread will not make >> things more scalable, because you have a single thread anyway. You'd >> need to go BQL-free and allow an arbitrary number. >> >>> Moving things to AIO isn't deviation, it's more about enabling of dataplane >>> and >>> epoll. That's why block was moved to AioContext, and I think we can do >>> similar >>> for net and serial, the difference is that as a start, they don't need to be >>> fully BQL-free like virtio-blk and scsi. But by running in an aio_poll() >>> loop, >>> they can better performance because of epoll. >> >> Isn't that what your "iohandler.c with AioHandler" already does? True, >> it would be epoll-within-poll, not pure poll. But if you need epoll, >> you might as well go BQL-free. > > epoll-within-poll? Do you mean change the main event loop from: > > qemu_poll_ns([..., ioeventfd1, ioeventfd2, ..., ioeventfd99], ...) > > to > > qemu_poll_ns([epollfd], ...) > > where epollfd watches all the fds, and let the handler of epollfd do > epoll_wait()?
I mean that glib's main loop (or os_host_main_loop_wait in main-loop.c) uses poll, and then the AioContext GSource uses epoll. Still, you have a constant (and low) number of file descriptors in the outer poll. Paolo
