QT4 Tray application and CPU load in 18.04

[Stefan]

Ubuntu 18.04 LTS
Session: gnome-flashback
Tested with: gnome-panel: 3.26.0-1ubuntu5 / 3.28.0-1ubuntu1 (cosmic)

We recognized a steady CPU load of about 2% when starting our QT4 tray application. To eliminate any issues in our application, we created a minimal python qt4 tray app (attached).

As soon as this app is started, the gnome-panel process gets a CPU load of about 2%.
When stracing the gnome-panel, we recognize a repeating log pattern:

poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN}], 3, 0) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
writev(3, [{iov_base="\212\5\4\0f\26 \0\0\0\26\0\26\0\2\0\217\3\4\0U\1 \0f\26 \0\0\0\0\0"..., iov_len=40}, {iov_base=NULL, iov_len=0}, {iov_base="", iov_len=0}], 3) = 40
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN}], 3, 13) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
writev(3, [{iov_base="5 \4\0g\26 \0\3\0 \0\26\0\2\0\213\4\6\0h\26 \0g\26 \0&\0\0\0"..., iov_len=236}, {iov_base=NULL, iov_len=0}, {iov_base="", iov_len=0}], 3) = 236
recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="[\2\353kT\1 \0U\1 \0\200)y\0\0\0\26\0\26\0\2\0\n\5h\3\26\0\30\0", iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 32
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN}], 3, 0) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
writev(3, [{iov_base="\212\5\4\0i\26 \0\0\0\26\0\26\0\2\0\217\3\4\0U\1 \0i\26 \0\0\0\0\0"..., iov_len=40}, {iov_base=NULL, iov_len=0}, {iov_base="", iov_len=0}], 3) = 40
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN}], 3, 13) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
writev(3, [{iov_base="5 \4\0j\26 \0\3\0 \0\26\0\2\0\213\4\6\0k\26 \0j\26 \0&\0\0\0"..., iov_len=236}, {iov_base=NULL, iov_len=0}, {iov_base="", iov_len=0}], 3) = 236
recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="[\2\371kT\1 \0U\1 \0\217)y\0\0\0\26\0\26\0\2\0\n\5h\3\26\0\30\0", iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 32
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN}], 3, 0) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])

The trayapp is doing nothing. Can anybody explain how to stop this behaviour in gnome-panel? Thanks!

[Dmitry Shachnev (mitya57)]

Qt 4 is no longer supported. Does it happen with Qt 5?

[Stefan (steffel)]

Tried the same python minimal application with pyqt5 (qt 5.9.5) - and no, it does not happen.

So it seems to be a QT4 problem somehow in connection to the gnome-panel, because this does not happen with the same QT4 application and fbpanel in the same environment.

stracing the gnome-panel with this pyqt5 app, a similar output is logged, but not as frequent as with qt4:

restart_syscall(<... resuming interrupted poll ...>) = 1
recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\34\0\260\202\275\2\0\0\21\2\0\0:\201\247\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 32
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN}], 3, -1) = 1 ([{fd=3, revents=POLLIN}])
recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\34\0\260\202\275\2\0\0\21\2\0\0R\324\247\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 32
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable)
poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN}], 3, -1

I attached the pyqt5 tray app if somebody wants to take a look at that.
But the CPU load disappears with QT5.

[Dmitry Shachnev (mitya57)]

I think it is a bug in sni-qt that sends too many events to gnome-panel. Other panels like fbpanel do not use indicators so the X11 tray is used there, which does not have the issue.

sni-qt is also unmaintained so I doubt that this will be fixed.

You can use the X11 tray with gnome-panel too, by removing sni-qt package and adding “Notification area” applet to the panel.

If you want to further debug the issue, output of dbus-monitor may be more interesting than strace output.

[Stefan (steffel)]

I thought, the QSystemTrayIcon is in the notification area, automatically. Because we have this area activated and it only appears within this area.

Here ist the output of dbus-monitor:

QT4 app:

method call time=1530618711.195260 sender=:1.901 -> destination=org.freedesktop.DBus serial=1 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=Hello
method return time=1530618711.195277 sender=org.freedesktop.DBus -> destination=:1.901 serial=1 reply_serial=1
   string ":1.901"
signal time=1530618711.195283 sender=org.freedesktop.DBus -> destination=(null destination) serial=5 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
   string ":1.901"
   string ""
   string ":1.901"
signal time=1530618711.195291 sender=org.freedesktop.DBus -> destination=:1.901 serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameAcquired
   string ":1.901"
method call time=1530618711.195759 sender=:1.901 -> destination=org.freedesktop.DBus serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',member='NameOwnerChanged',arg0='org.gnome.GConf'"
method call time=1530618711.199344 sender=:1.901 -> destination=org.freedesktop.DBus serial=3 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='method_call',interface='org.gnome.GConf.Database',member='Notify'"
method call time=1530618711.199795 sender=:1.901 -> destination=org.freedesktop.DBus serial=4 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',interface='org.gnome.GConf.Server',member='Bye'"
method call time=1530618711.200079 sender=:1.901 -> destination=org.freedesktop.DBus serial=5 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',member='Disconnected'"
method call time=1530618711.200335 sender=:1.901 -> destination=org.freedesktop.DBus serial=6 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=StartServiceByName
   string "org.gnome.GConf"
   uint32 0
method return time=1530618711.200347 sender=org.freedesktop.DBus -> destination=:1.901 serial=3 reply_serial=6
   uint32 2
method call time=1530618711.200694 sender=:1.901 -> destination=org.gnome.GConf serial=7 path=/org/gnome/GConf/Server; interface=org.gnome.GConf.Server; member=GetDefaultDatabase
method return time=1530618711.200704 sender=:1.79 -> destination=:1.901 serial=217 reply_serial=7
   object path "/org/gnome/GConf/Database/0"
method call time=1530618711.200822 sender=:1.901 -> destination=org.gnome.GConf serial=8 path=/org/gnome/GConf/Database/0; interface=org.gnome.GConf.Database; member=LookupExtended
   string "/desktop/gnome/interface/menus_have_icons"
   string "en_US.UTF-8"
   boolean true
method return time=1530618711.200836 sender=:1.79 -> destination=:1.901 serial=218 reply_serial=8
   struct {
      string "/desktop/gnome/interface/menus_have_icons"
      struct {
         int32 4
         boolean false
      }
      boolean true
      string "/schemas/desktop/gnome/interface/menus_have_icons"
      boolean true
      boolean true
   }
signal time=1530618711...

[Dmitry Shachnev (mitya57)]

> Could not get owner of name 'org.kde.StatusNotifierWatcher': no such name

Oh, it looks like I was wrong then.

There are two ways to get icons in the panel: via indicator-application and via the old X11 tray.

The indicator-based tray is default if you have the standard panel configuration (with indicator-applet added to the panel). But it looks like you don’t have it, so the X11 tray is used instead.

You can try adding indicator-applet to the panel and see if this helps.

[Stefan (steffel)]

It was not a big task to convert my application to a qt5 app, which I did this afternoon. The CPU load is gone, now, and for me, this is the solution to my problem.

I appreciate your help, thanks!

[Launchpad Janitor (janitor)]

[Expired for gnome-panel (Ubuntu) because there has been no activity for 60 days.]