The LXF Benchmark: Desktop environments

It's widely accepted that Gnome and KDE are the heaviest Unix desktops, while Xfce is lighter and faster. Yet many accuse Xfce of piling on the pounds in recent releases, and debates rage on as to whether Gnome or KDE is the king of the memory munchers. So we've gathered together some extensive benchmarks to find out the real story.

A desktop environment (DE) is not a window manager (WM) - the latter is a program which only draws and manages all the windows on your screen. A desktop environment is a homogeneous collection of tools, from window and file managers to hardware configuration utilities and (theoretically) any other application you may ever need. "Homogeneous" means that all pieces share the same base libraries and design guidelines, reusing interfaces (eg the file selector) and communicating with one another in various ways, from copy and pasting to opening a browser whenever you click on a URL.

For our tests we used the desktops packaged in Fedora 9 (this article was written just before Fedora 10 was released): Gnome 2.22.3, KDE 4.1.2 and Xfce 4.4.2. Our test machine was a dual-core AMD 64 3800+ system with 2 GB of RAM.

Early Gnome 2 releases were notoriously sluggish,
but the desktop has improved over the years.

Starting from the top

We created a separate user account with default settings for each DE and then ran the top command, with the $HOME/.toprc configuration file of Listing 8 (at the bottom of this article), and took several measurements. Eventually, all measurements of the same type were combined in one listing. You can read the definitions of the parameters in each listing in the top man page. Here, for brevity, we'll just note that RES is supposed to give you an idea of how much physical RAM an application is actually using. Stats can vary from system to system, so RES is not a laser-focused and exact indication of RAM usage - view these numbers as ballpark figures for a general idea of how much memory a desktop uses.

The questions we asked are:

• How much disk space does each DE needs?
• How much RAM does it consume just to stand up, waiting for input?
• What are the minimum RAM requirements of its most basic applications (file manager, text editor, X terminal?)

The most notable facts are that KDE is relatively slow to start and Xfce, while not the fastest, takes much less space on disk than its competitors.

Listing 1: Startup time, number of packages and disk usage for each DE:

            Startup time   # of packages   Total Size (MB)
  Gnome:    11s            268             ~200 MB
  KDE:     ~22s            138             335 MB
  Xfce:     14s            20              30 MB

Xfce also has the lightest file manager, Thunar:

Listing 2: File Manager displaying home directory (RES column is most important):

                     PID VIRT  RES  SHR S %CPU %MEM SWAP CODE DATA
  
  GNOME (Nautilus): 2602 500m  72m  12m S  1.0  3.7 428m 1280 152m
  KDE (Dolphin):    2852 339m  20m  14m S 10.9  1.0 319m  416 5852
  XFCE (Thunar):    2671 254m  10m 8100 S  0.7  0.6 244m  528  32m

The load mentioned in the next lists consisted of showing (S) and then copying (C) a folder containing 1642 JPEG pictures, occupying a total of 3.6GB:

Listing 3: File managers under load (RAM):

                      VIRT  RES  SHR S %CPU %MEM SWAP CODE DATA COMMAND
  
  GNOME (Nautilus): S 681m 202m  12m R 98.7 10.4 478m 1280 331m
  GNOME (Nautilus): C 718m 233m  12m D 17.6 12.0 485m 1280 368m
  KDE (Dolphin):    S 385m  33m  16m S 18.6  1.7 351m  416  16m dolphin
                      294m  32m 7528 R 95.6  1.7 262m   44  24m kio_thumbnail
  KDE (Dolphin):    C 388m  36m  16m S 13.6  1.9 351m  416  20m dolphin
                      242m 6592 3844 D 10.0  0.3 236m   44 2444 kio_file
                      242m 6208 3844 S  9.6  0.3 236m   44 2036 kio_file
  XFCE (Thunar):    S 429m  25m 9972 S  0.3  1.3 403m  528 182m
  XFCE (Thunar):    C 431m  28m  12m S 33.2  1.5 403m  528 182m

Listing 4: File manager under stress (times):

                     Show      Copy
  GNOME (Nautilus):  2m55s     3m27s
  KDE (Dolphin):     2m50s     3m38s
  XFCE (Thunar):     2m46s     3m45s

Plasma and other parts of KDE 4 make it start quite slowly,
but once it's up and running things aren't so bad.

Thunar was the lightest on RAM, while Dolphin was terribly slow and memory hungry both to display thumbnails and copy files. The leanest text editor is Xfce's Mousepad, while the terminal emulators have all more or less the same requirements.

Text editors and terminals

Listing 5: Text Editor

                     PID VIRT  RES  SHR S %CPU %MEM SWAP CODE DATA
  GNOME (gedit):    2748 320m  14m  10m S  2.3  0.7 305m  616 3704
  KDE (kwrite):     2820 354m  22m  16m S  1.7  1.2 331m    4 5496
  Xfce (mousepad):  2742 170m 7712 6012 S  0.7  0.4 163m   72 1608

Listing 6: X terminal

                          PID  VIRT  RES  SHR S %CPU %MEM SWAP CODE DATA
  GNOME (gnome-terminal): 2863 333m  13m 9772 S  1.0  0.7 320m  256  13m
  KDE (konsole):          2800 349m  15m  10m S  1.0  0.8 334m    4  78m
  Xfce (xfce4-terminal):  2719 244m  12m 8888 S  1.0  0.6 232m  152 3460

There are several facts, both technical and not technical, to take into account in order to understand the meaning of the listings. First of all, if you have enough RAM to run all the programs you need without swapping, every DE may feel adequately fast. This is especially true because what often slows down a desktop is the X server (about 30MB before you even log in) and the user programs you run. For instance, a spreadsheet with thousands of columns and complicated formulas, a program which leaks memory, or a web portal full of JavaScript and Flash are all do more to degrade performance than the DE.

Moreover, end user programs and DE basic components interact with each other in nasty, mysterious ways which may even differ from distro to distro. If desktop A uses twice as much RAM as desktop B just by waiting for you to touch the keyboard, this may be because it has already loaded all the shared libraries that, say, your favourite email client needs. In such a case, writing and reading email may require less memory and swapping, and will therefore be faster, on desktop A. Other things that can make numbers less reliable are whether (and how much) an application uses threads, or the average size of the files you load in it: these are all things which may increase the usage of swap and make your computer much less responsive. Of course, if a desktop needs to dip into swap just to start up, you need to make the most effective use of your RAM - eg a slick window manager like Blackbox or its derivatives.

Xfce's terminal and text editor are by far the
lightest of the bunch, although Mousepad doesn't compare
to KWrite and gEdit in feature terms.

Putting it all together

So lastly, here's a summary chart of the three desktops in their idle states, showing the RAM usage of their main components:

Listing 7: Idle desktop memory usage (RES column is most important)

  
          PID VIRT  RES  SHR S %CPU %MEM SWAP CODE DATA COMMAND
  GNOME:
         2386 135m  38m 8280 S  1.0  2.0  96m 1688  30m Xorg
         2598 193m 9024 7112 S  1.3  0.5 184m  540 1780 metacity
         2725 323m  12m 9104 S  1.3  0.7 310m  256  13m gnome-terminal
         2572 332m   9m 7716 S  0.3  0.5 322m   36  22m gnome-settings-
         2600 323m  15m  10m S  0.3  0.8 307m  544 4280 gnome-panel
         2588 213m 2244 1232 S  1.0  0.1 210m  164  820 gnome-screensav
  KDE:
         2400 169m  43m 5940 S  4.3  2.2 125m 1688  37m Xorg
         2820 354m  22m  16m S  1.7  1.2 331m    4 5496 kwrite
         2646 284m  16m  13m S  1.3  0.9 267m    4 3944 kwin
         2800 349m  15m  10m S  1.0  0.8 334m    4  78m konsole
         2662 517m  28m  16m S  0.7  1.5 488m    4 105m plasma
         2698 295m 9980 8192 S  0.3  0.5 285m    4 1408 klipper
         2760 213m 7776 5988 S  0.3  0.4 206m    4 1032 kded
  XFCE:
         2395 136m  25m 8456 S  1.2  1.3 110m 1688  16m Xorg
         2661 213m 2528 1512 S  0.3  0.1 210m  164  816 gnome-screensaver
         2665 293m 5032 2588 S  0.3  0.3 289m   16  12m xfce-mcs-manager
         2742 170m 7712 6012 S  0.7  0.4 163m   72 1608 mousepad
         2666 179m 7300 5800 S  0.3  0.4 172m  288 1324 xfwm4
         2673 232m 9460 6884 S  0.3  0.5 222m  104 2472 xfce4-panel
         2682 244m 8792 6288 S  0.3  0.4 235m   44  12m xfce4-mixer-plugin

Final stats: So from this chart, the total RAM usage for Gnome's main components is 85MB, the total for KDE is 140MB, and for Xfce it's 66MB. As mentioned, these are the results from one set of tests - results will vary from distro to distro, and are affected by many factors such as the optimisation flags used to build the software. It's important that these figures aren't analysed too deeply, but instead seen as a roundabout approximation of Linux desktop memory usage.

We conclude this article with an invitation: copy the top configuration file of Listing 8 in your home directory, start your favourite apps, run top and then paste in a comment here its output, together with your Linux distribution, CPU type and amount of RAM. Let's see who can do more with less!

Listing 8: $HOME/.toprc

  RCfile for "top with windows"           # shameless braggin'
  Id:a, Mode_altscr=0, Mode_irixps=1, Delay_time=3.000, Curwin=0
  Def     fieldscur=AEHIOQTWKNmbcdfgjPlRSuvyzX
          winflags=62777, sortindx=10, maxtasks=0
          summclr=1, msgsclr=1, headclr=3, taskclr=1
  Job     fieldscur=ABcefgjlrstuvyzMKNHIWOPQDX
          winflags=62777, sortindx=0, maxtasks=0
          summclr=6, msgsclr=6, headclr=7, taskclr=6
  Mem     fieldscur=ANOPQRSTUVbcdefgjlmyzWHIKX
          winflags=62777, sortindx=13, maxtasks=0
          summclr=5, msgsclr=5, headclr=4, taskclr=5
  Usr     fieldscur=ABDECGfhijlopqrstuvyzMKNWX
          winflags=62777, sortindx=4, maxtasks=0
          summclr=3, msgsclr=3, headclr=2, taskclr=3