Re: Emacs uses 100% cpu time

[Richard Stallman]

    According point "** If the symptom of the bug is that Emacs fails to
    respond" I stopped emacs with C-z in the terminal GDB is running in and
    typed finish till the call didn't return anymore. That was in
    wait_reading_process_output.

That function is waiting for keyboard input which does not arrive.
That is normal when Emacs is idle.

    #32 0x0818b2e8 in wait_reading_process_output (time_limit=30, microsecs=0,
        read_kbd=-1, do_display=1, wait_for_cell=137459913, wait_proc=0x0,
        just_wait_proc=0) at process.c:4343

That line is a call to timer_check.  Apparently Emacs is running a timer
over and over.  You need to investigate the data in a few frames
directly inside this one, to see which timer is running.

You omitted the first 31 frames; what do they say?

     So I pressed C-z again and stepped through
    that frame with next:

    (gdb) finish
    Run till exit from #0  0x0818b2e8 in wait_reading_process_output (
        time_limit=30, microsecs=0, read_kbd=-1, do_display=1,
        wait_for_cell=137459913, wait_proc=0x0, just_wait_proc=0) at 
process.c:4343

    Program received signal SIGTSTP, Stopped (user).
    0x08141c3c in mark_object (arg=151918113) at alloc.c:5447
    5447    {
    (gdb) next

That time you hit it inside a GC.  It appears that there's no problem
with GC.  So just continue, when you're inside GC.