bug#22305: 24.5; permanent 100% CPU load for no apparent reason

bug#22305: 24.5; permanent 100% CPU load for no apparent reason

[Roland Winkler]

Lately emacs gives me some strange problem, where according to `top'
the CPU load due to the emacs process goes up to a permanent value
of 100% (and I notice this because the laptop fan starts spinning
loudly), whereas according to `ps' the emacs process continues to
give rise to only a marginal CPU load.  While this happens, emacs
responds normally, so it appears that emacs is not trying to do
anything unusual in the background.

I did not have this problem while I was using emacs 24.5 under
ubuntu 14.04.  It only appeared lately when I upgraded to a new
laptop running ubuntu 15.10.  I am not aware of any significant
change in my emacs configuration since I made this switch.

What can I do to pin this down further?  So far, I have not noticed
anything that triggers this behavior reproducibly and my workaround
has been to restart emacs.  But that's not nice for a recurring
problem (about once per day).



In GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.7)
 of 2015-11-24 on regnitz
Windowing system distributor `The X.Org Foundation', version 11.0.11702000
System Description:	Ubuntu 15.10

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: 
  locale-coding-system: utf-8-unix

bug#22305: 24.5; permanent 100% CPU load for no apparent reason

[Eli Zaretskii]

> Date: Mon, 4 Jan 2016 10:48:02 -0600
> From: "Roland Winkler" <winkler@gnu.org>
> 
> Lately emacs gives me some strange problem, where according to `top'
> the CPU load due to the emacs process goes up to a permanent value
> of 100% (and I notice this because the laptop fan starts spinning
> loudly), whereas according to `ps' the emacs process continues to
> give rise to only a marginal CPU load.  While this happens, emacs
> responds normally, so it appears that emacs is not trying to do
> anything unusual in the background.

Not necessarily.  AFAIR, 'top' shows the CPU usage of each program in
terms of processor execution units.  IOW, 100% means Emacs is pegging
a single execution unit.  How many execution units (cores) do you have
on that system?

> What can I do to pin this down further?  So far, I have not noticed
> anything that triggers this behavior reproducibly and my workaround
> has been to restart emacs.  But that's not nice for a recurring
> problem (about once per day).

When this happens, attach a debugger and show us the backtrace,
including the Lisp backtrace.

bug#22305: 24.5; permanent 100% CPU load for no apparent reason

[Roland Winkler]

On Mon Jan 4 2016 Eli Zaretskii wrote:
> Not necessarily.  AFAIR, 'top' shows the CPU usage of each program
> in terms of processor execution units.  IOW, 100% means Emacs is
> pegging a single execution unit.

Sure.  My point is that normally `top' says that my emacs session
does not take more than 2 or 3% CPU load.  Yet suddenly this goes up
to 100% and the fan starts running loudly, too.

> How many execution units (cores) do you have on that system?

`lshw' says

  Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz

which, I believe, comes with four cores.

> When this happens, attach a debugger and show us the backtrace,
> including the Lisp backtrace.

Thanks, will do that.

bug#22305: 24.5; permanent 100% CPU load for no apparent reason

[Glenn Morris]

Since the best part of a year has passed with no further information,
I'm closing this. Please reopen if you can provide the requested
information.

bug#22305: 24.5; permanent 100% CPU load for no apparent reason

[Michael Heerdegen]

Eli Zaretskii <eliz@gnu.org> writes:

> When this happens, attach a debugger and show us the backtrace,
> including the Lisp backtrace.

Using profiler.el might also reveal what Emacs is doing.


Michael.