>>> On 4/1/2015 at 05:14 PM, Cole Robinson <crobinso@xxxxxxxxxx> wrote: > On 04/01/2015 05:42 PM, Charles Arnold wrote: >> Under certain conditions I see the guest CPU usage display not >> being updated. The problem seems most prevalent when Xen >> is the underlying hypervisor but I have seen it occasionally with >> KVM. >> >> What appears to be happening is that when a VM is created, the >> engine's _handle_tick_queue() calls the connection tick() method >> which in turn calls _tick(). In here it calls _update_vms() which >> gets a new vmmDomain object. Then it spawns a new thread to >> call tick_send_signals() where if 'pollvm' is True then 'self._vms' >> will get the newly create vmmDomain object. >> >> The problem (I think) is that under certain conditions the thread >> spun up by self.idle_add(tick_send_signals) doesn't run quickly >> enough (and therefore doesn't set self._vms) until after _tick() returns >> and is called again and second vmmDomain object is created. >> >> At this point it appears that the first vmmDomain object collects the >> cpu stats from libvirt while the second vmmDomain object updates >> the display which doesn't have the stats and therefore nothing appears. >> > > That analysis sounds reasonable. Since tick() is running in a thread, if the > mainloop is handling lots of UI stuff or similar it seems possible that > tick() > could be invoked twice before the mainloop handles tick_send_signals. > > Unfortunately our threading model is pretty hacky here since we have threads > touch a bunch of shared state without any locking, but it's simple and > generally works out fine. > >> Below are a couple approaches to solving the problem (assuming >> my analysis is correct). This first one simply yields to give the >> tick_send_signals thread a chance to run. >> > >> diff --git a/virtManager/connection.py b/virtManager/connection.py >> index a907a3f..af27141 100644 >> --- a/virtManager/connection.py >> +++ b/virtManager/connection.py >> @@ -1240,6 +1240,9 @@ class vmmConnection(vmmGObject): >> self._change_state(self._STATE_ACTIVE) >> >> self.idle_add(tick_send_signals) >> + if len(self._vms) < len(vms): >> + # Allow time for tick_send_signals to run >> + time.sleep(.1) >> >> ticklist = [] >> def add_to_ticklist(l, args=()): >> > > Obviously a timeout is sketchy since it might just make it less likely to > trigger. > >> This second solution doesn't wait for the thread and sets self._vms >> if pollvm is True. >> >> diff --git a/virtManager/connection.py b/virtManager/connection.py >> index a907a3f..96c208e 100644 >> --- a/virtManager/connection.py >> +++ b/virtManager/connection.py >> @@ -1240,6 +1240,8 @@ class vmmConnection(vmmGObject): >> self._change_state(self._STATE_ACTIVE) >> >> self.idle_add(tick_send_signals) >> + if pollvm: >> + self._vms = vms >> >> ticklist = [] >> def add_to_ticklist(l, args=()): >> >> Any thoughts on this problem and the potential solutions? > > We can't update any of the conn lists in the thread since it's possible the > self._vms is in use by the mainloop, which can cause weird errors if it's > updated while another part of the code is iterating over it or similar. > > I think the proper thing to do short of some larger refactoring is to use a > threading.Lock(). conn.tick() will grab the lock at the start, > tick_send_signals will release the Lock when it's updated the conn state. So > tick() can't run until the previous tick_send_signals has finished. > > If you can reproduce easily, does this patch fix it (and not cause issues?). > I > only did light testing. Not pushed yet Thanks for the patch. I have a machine that reproduces the problem easily. I've tested your patch for both KVM and Xen and it fixes the problem without any adverse side effects that I was able to see. I started about a dozen installs on each (same machine booted either KVM or Xen) with a mix of ISO and network installation sources for KVM, Xen PV, and Xen HVM. I would say the patch is good. - Charles _______________________________________________ virt-tools-list mailing list virt-tools-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/virt-tools-list
