[Bug 281775] New: knotify4 is wasting CPU cycles

[Dima Ryazanov]

https://bugs.kde.org/show_bug.cgi?id=281775

           Summary: knotify4 is wasting CPU cycles
           Product: kde
           Version: unspecified
          Platform: Ubuntu Packages
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
        AssignedTo: unassigned-bugs at kde.org
        ReportedBy: dima at gmail.com


Version:           unspecified (using KDE 4.7.1) 
OS:                Linux

knotify4 is constantly using up about 2% of the CPU. Sure, it's not a lot, but
when dbus-daemon, udisks-daemon, amarok, etc. each use another 1-2%, it all
adds up. Even when doing a Google search for "knotify4", most of the results
are about knotify wasting CPU, so looks like it affects lots of people.

I've tried running strace and gdb, but the output doesn't look very
interesting:


$ strace -fp 2796
[pid  2796] read(7, 0x1737d34, 4096)    = -1 EAGAIN (Resource temporarily
unavailable)
[pid  2796] read(7, 0x1737d34, 4096)    = -1 EAGAIN (Resource temporarily
unavailable)
[pid  2796] poll([{fd=3, events=POLLIN}, {fd=7, events=POLLIN}, {fd=9,
events=POLLIN}, {fd=11, events=POLLIN}, {fd=5, events=POLLIN}, {fd=14,
events=POLLIN}], 6, 0) = 0 (Timeout)
[pid  2796] read(7, 0x1737d34, 4096)    = -1 EAGAIN (Resource temporarily
unavailable)
[pid  2796] read(7, 0x1737d34, 4096)    = -1 EAGAIN (Resource temporarily
unavailable)
[pid  2796] poll([{fd=3, events=POLLIN}, {fd=7, events=POLLIN}, {fd=9,
events=POLLIN}, {fd=11, events=POLLIN}, {fd=5, events=POLLIN}, {fd=14,
events=POLLIN}], 6, 0) = 0 (Timeout)
...

$ gdb -p 2796
...
Breakpoint 1, read () at ../sysdeps/unix/syscall-template.S:82
82      ../sysdeps/unix/syscall-template.S: No such file or directory.
        in ../sysdeps/unix/syscall-template.S
(gdb) bt
#0  read () at ../sysdeps/unix/syscall-template.S:82
#1  0x00007f32fe9e2f1d in ?? () from /usr/lib/x86_64-linux-gnu/libxcb.so.1
#2  0x00007f32fe9e33f8 in xcb_poll_for_event () from
/usr/lib/x86_64-linux-gnu/libxcb.so.1
#3  0x00007f3302d26099 in poll_for_event (dpy=0x1742750) at
../../src/xcb_io.c:256
#4  0x00007f3302d26161 in poll_for_response (dpy=0x1742750) at
../../src/xcb_io.c:288
#5  0x00007f3302d2688d in _XEventsQueued (dpy=0x1742750, mode=<optimized out>)
at ../../src/xcb_io.c:362
#6  0x00007f3302d1714f in XEventsQueued (dpy=0x1742750, mode=2) at
../../src/Pending.c:43
#7  0x00007f3304973a9c in x11EventSourceCheck (s=0x171fce0) at
kernel/qguieventdispatcher_glib.cpp:85
#8  0x00007f3300c2a844 in g_main_context_check (context=0x171f800,
max_priority=0, fds=<optimized out>, n_fds=<optimized out>)
    at /build/buildd/glib2.0-2.29.90/./glib/gmain.c:2959
#9  0x00007f3300c2b092 in g_main_context_iterate (context=0x171f800,
block=<optimized out>, dispatch=1, self=<optimized out>)
    at /build/buildd/glib2.0-2.29.90/./glib/gmain.c:3086
#10 0x00007f3300c2b539 in g_main_context_iteration (context=0x171f800,
may_block=1) at /build/buildd/glib2.0-2.29.90/./glib/gmain.c:3152
#11 0x00007f3303c7ded6 in QEventDispatcherGlib::processEvents (this=0x16facd0,
flags=<optimized out>) at kernel/qeventdispatcher_glib.cpp:422
#12 0x00007f3304973c6e in QGuiEventDispatcherGlib::processEvents
(this=<optimized out>, flags=<optimized out>) at
kernel/qguieventdispatcher_glib.cpp:204
#13 0x00007f3303c51cf2 in QEventLoop::processEvents (this=<optimized out>,
flags=...) at kernel/qeventloop.cpp:149
#14 0x00007f3303c51ef7 in QEventLoop::exec (this=0x7fff28105dd0, flags=...) at
kernel/qeventloop.cpp:201
#15 0x00007f3303c56789 in QCoreApplication::exec () at
kernel/qcoreapplication.cpp:1064
#16 0x0000000000409787 in ?? ()
#17 0x00007f330346130d in __libc_start_main (main=0x409140, argc=1,
ubp_av=0x7fff281061f8, init=<optimized out>, fini=<optimized out>,
rtld_fini=<optimized out>, 
    stack_end=0x7fff281061e8) at libc-start.c:226
#18 0x0000000000409865 in _start ()


Reproducible: Always

Steps to Reproduce:
Start KDE and run "top"

Actual Results:  
knotify4 is on top, using up 2% of CPU.

Expected Results:  
knotify should not be doing anything.

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