Overhead in 14.04 Comparing Xubuntu and Lubuntu

Nio Wiklund nio.wiklund at gmail.com
Mon May 5 19:21:45 UTC 2014

2014-05-05 19:24, Israel skrev:
> On 05/05/2014 11:08 AM, Aere Greenway wrote:
>> All:
>> In testing UbuntuStudio 14.04 (which uses the XFCE desktop), I have
>> been observing a surprising amount of overhead on slow machines. This
>> was surprising, given how well Lubuntu 14.04 performed doing the same
>> tests.
>> Since UbuntuStudio includes a lot of KDE libraries, I decided to
>> install Xubuntu 14.04 on my 450 megahertz Pentium III (512 MB RAM)
>> machine (an HP Vectra).  It took a very long time to install it.
>> The results of my testing of Xubuntu 14.04 corresponded to the testing
>> I did with UbuntuStudio.  It appears to be associated with the XFCE
>> desktop environment, and the overhead appears to be graphics-related
>> (the Xorg process using most of the CPU).
>> I don't know why there is such a radical difference between Lubuntu
>> (LXDE desktop), and Xubuntu (XFCE desktop), but I am sure of what I
>> observed on that particular machine.  These results correspond with
>> similar testing I have done on an HP deskpro 933 mhz (512 MB RAM)
>> machine, and also on a 1.7 gigahertz (1GB RAM) machine.  But I looked
>> most closely on the 450 Mhz (HP Vectra) machine.
>> Lubuntu Results:
>> After booting, with the resource monitor applet showing CPU and RAM,
>> fairly quickly the CPU usage went down to low values (6%), and stayed
>> there.
>> On starting a terminal window, and executing a "top" command, the CPU
>> usage returned to 6%.  I found that the terminal window could be
>> dragged around the screen much more easily than I remembered with
>> dragging other windows.
>> I started the Task Manager application, and observed the CPU usage
>> again go back down to around 6%.  However, when I tried to drag the
>> Task Manager window around the screen, it moved very slowly
>> (consistent with my past experience), and the CPU usage was near 100%
>> while moving it.  But when I released the window (and it stopped
>> moving), CPU usage went back to around 6%.
>> This closer look corresponds to my earlier testing, in which I
>> concluded that Lubuntu 14.04 works well on my 450 megahertz, 512
>> megabyte RAM machine, doing MIDI music with software synthesizers
>> (Qsynth and Qjackctl, in particular).  It passed my stress-test with a
>> complicated MIDI sequence file with no under-runs, which I was
>> particularly pleased with.
>> The only case I encountered overhead, was when I tried to drag windows
>> around the screen, and that was so bad that I stopped trying to drag
>> windows at all.
>> Xubuntu Results:
>> After booting, and signing-in, it takes a long time for the icons to
>> appear on the screen.  The CPU-graph applet on the task-bar stayed at
>> 100%.  When the icons finally appeared on the screen, the CPU-graph
>> applet finally went down to 83% usage, with no windows active.
>> I started up a terminal session, and ran a "top" command in it. That
>> showed that the Xorg process was using around 64% of the CPU (it
>> varied between 63% and 66%, but most often near 64%).  There was some
>> percent going to the CPU-graph (and System Monitor applets) in the
>> task-bar, but not anywhere near as much as the Xorg process.
>> I could drag the terminal session window around the screen with
>> similar performance as with Lubuntu).
>> I fired-up a Task Manager window, but could not identify in it
>> anything similar to the Xorg process.  I could drag the Task Manager
>> window around the screen, and it seemed to move at the same rate as
>> the terminal window (unlike my experience with Lubuntu, where a
>> graphics-oriented window moved much more slowly).
>> With the Task Manager window active, the "top" command running in the
>> terminal window showed the Xorg process using around 50% of the CPU
>> (it sometimes went higher), but it appeared to be because the Task
>> Manager process was using a significant amount of the CPU, and Xorg
>> could no longer use as much as it did on an idle system (the total
>> can't exceed 100%).
>> My overall impressions of testing both Xubuntu and UbuntuStudio on the
>> 450 megahertz machine is that it is way too slow to be practical to
>> use (as might have been apparent if anyone were listening to the words
>> I was muttering while doing the testing).
>> It appears that the excessive overhead is graphics-related.
>> Interestingly, at one point in testing, things were going very slow,
>> and I needed to do something to break it loose, but I really didn't
>> want to terminate Firefox.  I tried 'rolling-up' the Firefox window
>> (leaving only its title-bar, which incidentally, was now easy to drag
>> around the screen), and things seemed to then move forward in the
>> testing.
>> In my earlier testing on a 933 megahertz machine using UbuntuStudio, I
>> had reported (to the ZynAddSubFX developers) that ZynAddSubFX was no
>> longer usable on my 933 megahertz machine.  They did some checking,
>> and their testing didn't show any significant increase in the overhead
>> of their application.
>> From current results, I am now convinced that overhead is
>> graphics-related.
>> Conclusions:
>> Given the results in testing Xubuntu and UbuntuStudio (both XFCE
>> desktop), I can see why Ali insisted that 14.04 will not perform well
>> on low-spec machines.  From what Ali has said, he has been testing
>> Xubuntu and Ubuntu-Gnome.  I don't know what testing he did with
>> Lubuntu 14.04, and I have not yet tested Ubuntu-Gnome on a slower
>> machine.
>> But my testing of Lubuntu 14.04 on the same low-spec machines (at
>> least, the machines I have), shows that the system performs well
>> (until you try to drag a window around the screen).
>> I don't know why there is such a radical difference in the performance
>> of the XFCE desktop, and the LXDE desktop.
>> The Ubuntu Unity desktop performs poorly on my 1.7 gigahertz, 1
>> gigabyte RAM machine, though I am able to easily drag windows around
>> the screen (it has a NVIDIA graphics card).  My impressions are (I
>> haven't attempted to measure it yet) that it performs more poorly than
>> Windows 7 on that same machine.
>> UbuntuStudio on that 1.7 Ghz machine also performs poorly (it worked
>> fine in level  13.10), now (with 14.04) it is barely usable.
>> I think it would be useful for other people with low-spec machines to
>> see if they can duplicate my test results.
>> All of this poor performance is not apparent in fast machines.  It
>> only becomes apparent when you test on slower machines.
> I (and others) have observed the slow window dragging on low spec iBooks.
> It seems to me that installing xcompmgr helped.  If you could test it
> and report back that would be helpful, as I might just be imagining a
> difference because I like semi-transparent terminals SOOOOO much. :D
> It would be a waste of time to try to use (daily) something as heavy as
> XFCE on my iBook.  However, I have one that I am going to test
> reinstalling Lubuntu 14.04 on soon, so I may try using UbuntuStudio
> 14.04 (since I already have the ISO) and telling you how it goes.
> I fully expect it to be slow.
> Unity doesn't perform well on any machines with around 1Gig... I think
> you need at least 3 or 4 for it to be a really slick machine.  I can
> bare it on a 2Gig, but it isn't as fast as XFCE on the same hardware. 
> Oddly enough I found Lubuntu and Xubuntu to be about the same on a
> machine with that much memory.  The difference shows on machines with
>> 1Gig.  When you have less than 512 it becomes harder to use LXDE. 
> around 128 I pretty much will only use jwm, and Slim (instead of
> lightdm), as it performs close to Lubuntu on a 512 machine (some apps
> still take a looooong time to load)

Hi Aere and Israel,

@Aere, First of all, thanks for sharing your test results :-)

I agree that LXDE is better for low end computers, but was not aware of
the big difference. I guess the concept of a 'sweet point' may apply,
where a distro/flavour/desktop environment start working well. And this
sweet point may have a horsepower coordinate and a memory coordinate.

@Israel, Interesting point about xcompmgr :-)

@Aere, I think you have some old Intel graphics. Will UXA graphics
change the speed of it?

I have also read somewhere, that XFCE can be quite efficient with low
end computers, while Xubuntu is more demanding, because it is running
more processes. You could start from the Ubuntu mini.iso and install
xfce4 and compare the performance. Of course you can also install LXDE
in a similar way, or 'only' Openbox.

Finally, what about the low latency kernel (that you can always install,
and that comes with Ubuntu Studio)?

Best regards

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