[Eug-lug] ubuntu xterm strangeness

[Bob Miller]

Mike Cherba wrote:

> I noticed this when I was booting a system attached to a USB serial
> device, but eventually localized the issue to xterm itself.  Basically
> when you put a lot of text through an xterm the cpu usage on gutsy goes
> way up.  like 100%.  I've tried the same thing with the generic terminal
> app gnome-terminal and the cpu usage is much lower.  This seems odd.
> I'm wondering if there is something broken or at least terribly
> sub-optimal in one of the libraries used.

I did some benchmarking.  If xterm uses its default font, fixed, it
has about 16x higher throughput than gnome-terminal.  If both use the
same freetype font, xterm has 0.4x the throughput of gnome-terminal.

In all cases, one CPU is pegged.

Under xterm, font fixed:
    % time sh -c 'od /boot/vmlinuz-2.6.22-14-generic | head -100000'
    0.204u 0.100s 0:08.05 3.7%      0+0k 0+0io 0pf+0w

Under gnome-terminal, default font (dunno what it is):
    % time sh -c 'od /boot/vmlinuz-2.6.22-14-generic | head -100000'
    0.212u 0.100s 2:14.62 0.2%      0+0k 0+0io 0pf+0w

Under xterm, font "monospace 9":
    % time sh -c 'od /boot/vmlinuz-2.6.22-14-generic | head -100000'
    0.204u 0.076s 5:24.08 0.0%      0+0k 0+0io 0pf+0w

Under gnome-terminal, font "monospace 9":
    % time sh -c 'od /boot/vmlinuz-2.6.22-14-generic | head -100000'
    0.204u 0.084s 2:16.31 0.2%      0+0k 0+0io 0pf+0w


Top and gkrellm showed that the X server was pegged at 99-100% each
time, so we're really measuring the X server's font rendering speed.
Neigher xterm nor gnome-terminal uses significant CPU - 0.3 seconds
user+sys.

So the first question is, are you using a Freetype font on xterm?

-- 
Bob Miller                              K<bob>
                                        kbob at jogger-egg.com