bug#16995: 24.3; CPU usage spikes to 100% for minutes at a time

[Eli Zaretskii]

> From: Andrew Beekhof <andrew@beekhof.net>
> Date: Wed, 12 Mar 2014 18:08:27 +1100
> 
> I've been editing lots of python files in the last few days and noticed
> that Emacs has begun locking up for minutes at a time, for no apparent
> reason.
> 
> Example actions that can trigger the problem C-s (isearch-forward),
> pressing 'y' in response to query-replace prompts, typing, etc.
> Whether the buffer is saved or not makes no difference.
> 
> The only thing that really seems to help is switching back to a .c file.
> 
> Is this a known problem?
>  
> Example top output:
> 
> top - 17:44:11 up 29 days, 22:26,  3 users,  load average: 0.44, 0.50, 0.42
> Tasks: 236 total,   2 running, 233 sleeping,   0 stopped,   1 zombie
> %Cpu(s): 12.6 us,  0.1 sy,  0.0 ni, 87.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 
> st
> KiB Mem:   7871472 total,  7538448 used,   333024 free,   305676 buffers
> KiB Swap:  6029308 total,   731032 used,  5298276 free,  2390156 cached
> 
>   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
> 22971 beekhof   20   0  644976  49236  16308 R 100.1  0.6  19:33.79 emacs     
>                                                                               
>                                                                               
>                                                                         
> 26689 root      20   0   53020    272    176 S   0.7  0.0 308:17.91 plymouthd 
>                                                                               
>                                                                               
>                                                                         
> 
> A random blog suggested the following command might show something of
> interest. All I can tell is that thread 1 is quite deep.
> 
> # echo 't a a where' > gdb.cmd; gdb /usr/bin/emacs -p 22971 -x gdb.cmd 2>&1 
> </dev/null | tee /tmp/emacs.crash.backtrace
> GNU gdb (GDB) Fedora 7.6.50.20130731-19.fc20

The backtrace you posted indicates that Emacs is in garbage
collection.  To see if this is indeed the cause of those "lockups",
could you please customize garbage-collection-messages to a non-nil
value, and then see if every time Emacs locks up there's a message in
the echo area announcing GC?