On Mon, May 06, 2013 at 11:26:06AM +0800, liu ping fan wrote: > On Sat, May 4, 2013 at 12:03 AM, Michael Roth <mdr...@linux.vnet.ibm.com> > wrote: > > These patches apply on top of qemu.git master, and can also be obtained > > from: > > git://github.com/mdroth/qemu.git qcontext > > > > OVERVIEW > > > > This series introduces a set of QOM classes/interfaces for event > > registration/handling: QContext and QSource, which are based closely on > > their GMainContext/GSource GLib counterparts. > > > > QContexts can be created via the command-line via -object, and can also be > > intructed (via -object params/properties) to automatically start a > > thread/event-loop to handle QSources we attach to them. > > > > The reference implementation of QContext is GlibQContext, which uses > > GMainContext/GSource interfaces underneath the covers, thus we can > > also attach GSource (and as a result, AioContexts) to it. > > > > As part of this series we also port the QEMU main loop to using QContext > > and drop virtio-blk's dataplane thread in favor of a GlibQContext thread, > > which virtio-blk dataplane attaches to via it's AioContext's GSource. > > > > With these patches in place we can do virtio-blk dataplane assignment > > like so: > > > > qemu ... \ > > -object glib-qcontext,id=ctx0,threaded=yes > > -drive file=file.raw,id=drive0,aio=native,cache=none \ > > -device virtio-blk,drive=drive0,scsi=off,x-data-plane=on,context=ctx0 > > > > And also gain the ability to assign a virtio-blk dataplane to the default > > QContext driven by the QEMU main iothread: > > > > qemu ... \ > > -drive file=file.raw,id=drive0,aio=native,cache=none \ > > -device virtio-blk,drive=drive0,scsi=off,x-data-plane=on,context=main > > > > The latter likely isn't particularly desirable, and the series is in rough > > shape in general, but the goal of this RFC to demonstrate the approach and > > get some feedback on how we might handle thread assignments for things like > > virtio-blk/virtio-net dataplane, and multi-threaded device models general. > > > > Input on this would be greatly appreciated. > > > > BACKGROUND > > > > There has been an outgoing discussion on qemu-devel about what event loop > > interface to consolidate around for virtio-blk dataplane, threaded > > virtio-net, > > and offloading device workloads to seperate threads in general. > > > > Currently the main candidates seem to be GLib GSources and AioContext, with > > virtio-blk/virtio-net dataplane being the use-cases under consideration. > > > > virtio-blk: > > > > In the case of virtio-blk dataplane, we need to drive virtqueue and AIO > > events. > > Since AioContext is used extensively throughout the block layer to drive > > AIO, > > it makes sense to re-use it here as we look toward pushing dataplane > > functionality deeper into the block layer to benefit from things like image > > format support/snapshots/etc. > > > > virtio-net: > > > > In the case of Ping Fan's virtio-net dataplane patches > > (http://thread.gmane.org/gmane.comp.emulators.qemu/196111/focus=196111), we > > need to drive virtqueue and NetClient peer events (such as TAP devices, or > > possibly things like slirp in the future). Currently NetClient events rely > > on > > IOHandler interfaces such as qemu_set_fd_handler(). These interfaces are > > global > > ones that rely on a single IOHandler list serviced by QEMU's main loop. An > > effort is currently underway to port these to GSources so that can be more > > easilly attached to other event loops (as opposed to the hooks used for the > > virtio-net dataplane series). > > > > Theoretically, much of the latter (such as TAP devices) can also be done > > around > > AioContext with some minor changes, but other NetClient backends such as > > slirp > > lend themselves to more open-ended event loop interfaces like GSources. > > Other > > devices might also find themselves needing something more open-ended (a > > somewhat > > silly but present example being virtio-serial + GSource-driven chardev) > > > > QContext: > > > > Since the direction for the forseeable future will likely continue to be > > GSources for some things, AioContext for others, a way to reconcile these > > approaches would be the age-old approach of adding a layer of abstration on > > top of the 2 so that we can handle device/backend thread assignments using > > a general mechanism. Building around this abstration also leaves open the > > ability to deal with things like locking considerations for real-time > > support > > in the future. > > > > A reasonable start to modeling abstraction layer this would be the > > open-ended > > GMainContext/GSource approach that QEMU relies on already, which is what > > the QContext/QSource interfaces do (with some minor differences/additions > > such as QSources storing and opaque instead of the GSource-subclassing > > approach > > for GLib). > > > I think, custom-ed function for readable or not , ex, tap_can_send() > should be passed into QSource, but I failed to find such things in > [PATCH 3/9] QSource: QEMU event source object. Do I miss it?
We can actually do that via the prepare function. It gets called prior to polling the GPollFDs for that QSource/GSource. In the case where tap_can_send() == false, we'd simply zero out the GPollFD.events for the tap device in prepare(). One other interesting option this series opens up with regard to NetClient that currently use qemu_set_fd_handler(): We now have set_fd_handler(ctx, ...) interfaces, which assigns FD handlers to a specific QContext/event loop. So we don't actually need to convert all NetClients to GSources to offload handling to a dataplane thread. I think we'd still want to use a GSource for slirp though. Not saying that approach is better though, but maybe something to consider. > > Thanks and regards, > Pingfan > > TODO/KNOWN ISSUES > > > > - GTK UI causes a crash during certain window refresh events. works fine > > with > > VNC though, and no problems with other GSources. > > - slirp isn't working (will work with Ping Fan's slirp->GSource conversion) > > - add proper locking > > - integrate timers into a QSource to make timer-event driveable in seperate > > QContext event loops > > - consider a command-line wrapper to -object, such as: > > -context <id>,[threaded=<yes|no>],[backend=<default|glib>] > > > > Makefile.objs | 6 +- > > async.c | 16 +++ > > hw/block/dataplane/virtio-blk.c | 46 ++----- > > include/block/aio.h | 6 + > > include/hw/virtio/virtio-blk.h | 7 +- > > include/qcontext/glib-qcontext.h | 59 ++++++++ > > include/qcontext/qcontext.h | 76 +++++++++++ > > include/qcontext/qsource.h | 63 +++++++++ > > include/qemu/main-loop.h | 31 ++++- > > include/qom/object.h | 35 +++++ > > iohandler.c | 238 ++++++++++++++++++++++---------- > > main-loop.c | 96 ++++++------- > > qcontext/Makefile.objs | 1 + > > qcontext/glib-qcontext.c | 280 > > ++++++++++++++++++++++++++++++++++++++ > > qcontext/qcontext.c | 252 ++++++++++++++++++++++++++++++++++ > > qcontext/qsource.c | 143 +++++++++++++++++++ > > qom/Makefile.objs | 6 +- > > qom/object.c | 46 +++++++ > > tests/Makefile | 7 + > > tests/test-qcontext.c | 259 +++++++++++++++++++++++++++++++++++ > > vl.c | 2 + > > 21 files changed, 1512 insertions(+), 163 deletions(-) > > >
