VTE rendering slow.. [LWN.net]

VTE rendering slow..

Posted Jun 4, 2004 20:59 UTC (Fri) by kit (guest, #4609)
Parent article: The Grumpy Editor's guide to terminal emulators

The biggest problem with gnome-terminal is that with the move the VTE for rendering, CPU usage is through the roof. When compiling apps, gnome-terminal can consume more CPU than gcc.

scrolling speed

Posted Jun 5, 2004 0:48 UTC (Sat) by donio (guest, #94) [Link] (4 responses)

Indeed, rendering and scrolling speed is a very important consideration for me too. Here are the results of a little benchmark I just did with the terminal emulators I had handy. I ran the following command which prints 1000000 lines:

time seq -f 'teeeeeeeeeeeeeeeeeeeeeeeeeeeeeest %g' 1000000

The scrollback buffer was set to 1000 lines in each case (because that's about how much I use normally), scrollbars were enabled and jumpscroll was enabled where available (rxvt,xterm). The times are wall clock seconds:

gnome-terminal: 300.13
konsole: 33.311
rxvt: 9.741
xterm: 24.490

As you can see gnome-terminal is a dog, the rest of them did OK. rxvt rocks.

I remember that when I did a similar test a few years ago konsole was really slow while gnome-terminal was reasonable. I am happy to see that konsole got a lot better. It's a shame about gnome-terminal.

scrolling speed

Posted Jun 5, 2004 7:04 UTC (Sat) by jamesh (guest, #1159) [Link] (3 responses)

Out of interest, were you using the same fonts in each terminal emulator? For gnome-terminal, were you using a monochrome or antialiased font?

Did you use a core X font in xterm (set with the -fn argument), or a fontconfig font (set with the -fa/-fs arguments)? Does it make much of a difference if you put xterm into unicode mode?

Rxvt may be faster than the other terminal emulators, but its speed comes at the cost of features. You might not require some of the features found in the slower terminals, but some people can't do without them (a good example is the accessibility support found in gnome-terminal).

scrolling speed

Posted Jun 5, 2004 7:39 UTC (Sat) by donio (guest, #94) [Link] (2 responses)

For rxvt and xterm I specified the following font using X resources:

-*-lucidatypewriter-medium-r-*-*-*-120-*-*-*-*-iso8859-*

For gnome-terminal and konsole I tried selecting the same font using
menu selections. I had to select the size by pixels instead of points
but I think I got the same font.

Also, I normally run with

export GDK_USE_XFT=0

to disable the antialiased fonts in GTK (I like my fonts nice and
crisp, not fuzzy) so that was in effect too, but in my experience that
only increases the performance.

Terminal size was the default 80x25 size in all cases.

If you or anyone else has the time it would be great if you could try
reproducing this or do some similar test to make sure that the bad
gnome-terminal result is not caused by some peculiarity in my setup.

Thanks

scrolling speed

Posted Jun 5, 2004 11:06 UTC (Sat) by jamesh (guest, #1159) [Link] (1 responses)

Did you know that setting the GDK_USE_XFT environment variable to 0 will actually make VTE run slower? In pretty much all cases Xft will be faster than core fonts if you disable antialiasing, so most of the work goes into the default font rendering technology (which is now the only available font renderer for GTK in 2.4). So you actually deoptimised gnome-terminal for your tests.

If you prefer monochrome glyphs for a particular font, try putting something like this in your ~/.fonts.conf file:

<match target="font">
  <test name="family" compare="eq">
    <string>Terminal Font Name</string>
  </test>
  <edit name="antialias" mode="assign">
    <bool>false</bool>
  </edit>
</match>

You will probably need to restart gnome-terminal after the change in order for it to take effect.

Alternatively, you can just copy a bitmap font in uncompressed .pcf format to ~/.fonts and use that (the bitmap font will actually be faster to render too, which should improve performance). This should make it usable from gnome-terminal and any other terminal that can use Xft/fontconfig (such as xterm).

scrolling speed

Posted Jun 5, 2004 20:04 UTC (Sat) by donio (guest, #94) [Link]

Thank you for the advice, I appreciate your help!

I did some more testing this morning and here is what I found:

1. Yesterday I was *not* using the same font (lucidatypewriter) for
gnome-terminal that I used for the others. I must have left the "use
the system terminal font" setting on by accident. I am sorry about the
misleading numbers.

When I actually use lucidatypewriter I get 70 seconds instead of 300.

2. Even when using the system terminal font setting I am able to get
the 70s result by disabling antialiasing using your suggested .fonts.conf setting.

3. GDK_USE_XFT=0 doesn't seem to make a difference with the version of
gnome-terminal (2.4.2) and GTK (2.2.4) I have available. It doesn't
affect performance and it doesn't turn off antialiasing - I verified
that with xmag :)

70 seconds, while still a bit slower than the others (and a lot slower
than rxvt), is definitely major improvement over 300!

I will stop using GDK_USE_XFT=0 and learn about fontconfig.