Posting to xvid, mythtv, mplayer fedora and ivtv lists - Slow encoding by mencoder under FC2 faster under KnoppMyth. Why?

Hi,
        I am using mythTV under FC2 now ater moving from KnoppMyth this
    week-end. Following are the versions of the various software I use:

    FC2
    ivtv:    114z
    mythtv:    0.16
    xvid:    1.0.1 compiled using athlon specific architecture (using
rpmbuild
    and then installed the resulting RPMs)
    mplayer:    latest download from CVS
    kernel:    latest release from Fedora 2.6.8-521
    gcc:    gcc version 3.3.3 20040412 (Red Hat Linux 3.3.3-7)

    KnoppMyth
    ivtv:    113f
    mythtv:    0.16
    xvid:    1.0.1 compiled from tarball I got from xvid's site.
    mplayer:    same as that on FC2
    kernel:    2.4.25-chw
    gcc:    I don't know as I am not near my system and will have to go home
to
    check. KnoppMyth is R4V4 (so u may knwo the version of gcc)
    Platform:    Linux Fedora Core 2

    I run mplayer  (compiled on KnoppMyth) on KnoppMyth, I get 21 fps for
the
    first pass and 9 fps for the second. If I compile the same source for
    mplayer under FC2 and run under FC2, I get 9-12fps in the first pass
itself
    (Second pass shows the same result as that of on KnoppMyth, so no
problem).

    I am posting this message to more than one lists because it relates to
more
    than one lists and also I may find some-one using the same things I am
    trying to and reply with some solution.

    Thanks in advance.
    VJ