From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59773) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZaMGQ-0006Ri-1e for qemu-devel@nongnu.org; Fri, 11 Sep 2015 07:13:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZaMGP-0005gv-3i for qemu-devel@nongnu.org; Fri, 11 Sep 2015 07:13:05 -0400 Date: Fri, 11 Sep 2015 19:12:55 +0800 From: Fam Zheng Message-ID: <20150911111255.GD9241@ad.nay.redhat.com> References: <20150909032205.GA10922@ad.nay.redhat.com> <55F28D99.5060908@redhat.com> <20150911091433.GA6759@ad.nay.redhat.com> <20150911094425.GA9241@ad.nay.redhat.com> <55F2A4D6.6050009@redhat.com> <20150911104055.GB9241@ad.nay.redhat.com> <55F2B0EE.7030407@redhat.com> <20150911110122.GC9241@ad.nay.redhat.com> <55F2B4D7.4060801@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55F2B4D7.4060801@redhat.com> Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v2 11/11] block: Only poll block layer fds in bdrv_aio_poll List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: kwolf@redhat.com, qemu-block@nongnu.org, Alberto Garcia , qemu-devel@nongnu.org, stefanha@redhat.com On Fri, 09/11 13:02, Paolo Bonzini wrote: > > > 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. > OK, I think I get your idea, and it sounds good to me, thank you very much! ;-) Fam