Re: [libvirt] [[RFC] 0/8] Implement async QEMU event handling in libvirtd.

Hi Marc, Currently the block job handling needs to be sorted out before events can assume independent handling from RPC contexts. Sorry, I have not been able to revisit this in the past 2 months, but this is something I would very much like to fix. I will try looking up the exact dependency of the block layer so that this series could make some progress. regards, Prerna On Wed, Mar 21, 2018 at 1:24 PM, Marc Hartmayer <mhartmay(a)linux.vnet.ibm.com > On Tue, Oct 24, 2017 at 07:34 PM +0200, Prerna Saxena < > saxenap.ltc(a)gmail.com> > As noted in > > https://www.redhat.com/archives/libvir-list/2017-May/msg00016.html > > libvirt-QEMU driver handles all async events from the main loop. > > Each event handling needs the per-VM lock to make forward progress. In > > the case where an async event is received for the same VM which has an > > RPC running, the main loop is held up contending for the same lock. > > > > This impacts scalability, and should be addressed on priority. > > > > Note that libvirt does have a 2-step deferred handling for a few event > > categories, but (1) That is insufficient since blockign happens before > > the handler could disambiguate which one needs to be posted to this > > other queue. > > (2) There needs to be homogeniety. > > > > The current series builds a framework for recording and handling VM > > events. > > It initializes per-VM event queue, and a global event queue pointing to > > events from all the VMs. Event handling is staggered in 2 stages: > > - When an event is received, it is enqueued in the per-VM queue as well > > as the global queues. > > - The global queue is built into the QEMU Driver as a threadpool > > (currently with a single thread). > > - Enqueuing of a new event triggers the global event worker thread, which > > then attempts to take a lock for this event's VM. > > - If the lock is available, the event worker runs the function > handling > > this event type. Once done, it dequeues this event from the global > > as well as per-VM queues. > > - If the lock is unavailable(ie taken by RPC thread), the event > worker > > thread leaves this as-is and picks up the next event. > > - Once the RPC thread completes, it looks for events pertaining to the > > VM in the per-VM event queue. It then processes the events serially > > (holding the VM lock) until there are no more events remaining for > > this VM. At this point, the per-VM lock is relinquished. > > > > Patch Series status: > > Strictly RFC only. No compilation issues. I have not had a chance to > > (stress) test it after rebase to latest master. > > Note that documentation and test coverage is TBD, since a few open > > points remain. > > > > Known issues/ caveats: > > - RPC handling time will become non-deterministic. > > - An event will only be "notified" to a client once the RPC for same VM > completes. > > - Needs careful consideration in all cases where a QMP event is used to > > "signal" an RPC thread, else will deadlock. > > > > Will be happy to drive more discussion in the community and completely > > implement it. > > > > Prerna Saxena (8): > > Introduce virObjectTrylock() > > QEMU Event handling: Introduce async event helpers in qemu_event.[ch] > > Setup global and per-VM event queues. Also initialize per-VM queues > > when libvirt reconnects to an existing VM. > > Events: Allow monitor to "enqueue" events to a queue. Also introduce a > > framework of handlers for each event type, that can be called when > > the handler is running an event. > > Events: Plumb event handling calls before a domain's APIs complete. > > Code refactor: Move helper functions of doCoreDump*, syncNicRxFilter*, > > and qemuOpenFile* to qemu_process.[ch] > > Fold back the 2-stage event implementation for a few events : > > Watchdog, Monitor EOF, Serial changed, Guest panic, Nic RX filter > > changed .. into single level. > > Initialize the per-VM event queues in context of domain init. > > > > src/Makefile.am | 1 + > > src/conf/domain_conf.h | 3 + > > src/libvirt_private.syms | 1 + > > src/qemu/qemu_conf.h | 4 + > > src/qemu/qemu_driver.c | 1710 +++++++---------------------------- > > src/qemu/qemu_event.c | 317 +++++++ > > src/qemu/qemu_event.h | 231 +++++ > > src/qemu/qemu_monitor.c | 592 ++++++++++-- > > src/qemu/qemu_monitor.h | 80 +- > > src/qemu/qemu_monitor_json.c | 291 +++--- > > src/qemu/qemu_process.c | 2031 ++++++++++++++++++++++++++++++ > ++++-------- > > src/qemu/qemu_process.h | 88 ++ > > src/util/virobject.c | 26 + > > src/util/virobject.h | 4 + > > src/util/virthread.c | 5 + > > src/util/virthread.h | 1 + > > tests/qemumonitortestutils.c | 2 +- > > 17 files changed, 3411 insertions(+), 1976 deletions(-) > > create mode 100644 src/qemu/qemu_event.c > > create mode 100644 src/qemu/qemu_event.h > > > > -- > > 2.9.5 > > > > -- > > libvir-list mailing list > > libvir-list(a)redhat.com > > https://www.redhat.com/mailman/listinfo/libvir-list > > Hey Prerna, > > any updates so far? :) I’m just curious about the status of this series > as it would fix a performance problem we’ve. > > Thank you. > > Beste Grüße / Kind regards > Marc Hartmayer > > IBM Deutschland Research & Development GmbH > Vorsitzende des Aufsichtsrats: Martina Koederitz > Geschäftsführung: Dirk Wittkopp > Sitz der Gesellschaft: Böblingen > Registergericht: Amtsgericht Stuttgart, HRB 243294 > >