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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

    --
    /==============================\
    | David Mansfield |
    | lkml@dm.cobite.com |
    \==============================/

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