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SubjectRe: very poor performance in 2.5.66[-mm1]
On Fri, 28 Mar 2003, Andrew Morton wrote:
> > After all of the rave reviews about the interactivity fixes (both regular
> > and I/O scheduler related), I decided to give the 2.5.latest a try on my
> > desktop machine (system described below)
> >
> > I started X, everything seemed fine, maybe a bit faster. I opened a
> > 'gnome-terminal' and typed 'ls -ltr'. Wow, it was 20x slower.
> >
> > Here are the timings for 'ls -ltr':
> >
> > 2.5.66-mm1: 'ls -ltr' 31 seconds
> > 2.5.66-mm1: 'ls -ltr | cat' 2 seconds
> > 2.4.18-rhlatest: 'ls -ltr' 1.14 seconds
> How many files were there?

1337 files.

> My /usr/bin contains 3168 files. An `ls -ltr' in gnome-terminal takes 9.6
> seconds. In rxvt it takes 0.5 seconds. That's an 850MHz P3.
> So gnome-terminal appears to be a pretty slow application. My guess would be
> that something in the 2.5 kernel has exposed a marginality or an outright
> bug in it.

Yes. gnome-terminal is godawful slow on RHAT 8.0 (it does Xrender
alpha-channel crap for every character to get the anti-aliasing). But I
think the problem has to do with the pipe/pty wakeups. After 'ls' writes
a line to the pty, it seems as though the gnome-terminal is being woken up
(even though 'ls' has more to write), it's generating the Xrender
X-command and sending it to X. X is waking up and rendering it (which
forces a complete update of the screen).

Under 2.4.18-whatever, it would seem as though 'ls' is generating a large
number of lines of output before the gnome-terminal is waking up, causing
a dramatically fewer number of redraws.

> It would be interesting to edit include/asm-i386/param.h and set HZ to 100.

I'll try to check this out over the weekend.


| David Mansfield |
| |

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