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.
--
Sincerely,
Aere
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