netem in iproute2

[jiang20]

I just installed latest gentoo on my machine for network emulation. I tried to start netem by using :# tc qdisc add dev eth0 root netem delay 100ms
But I got an error:RTNETLINK answers: Invalid argument

It seems like that the netem function is disabled on current gentoo. And I read the Netem homepage found these:

if you run a current 2.6 distribution, (Fedora, OpenSuse, Gentoo, Debian, Mandriva), then netem is already enabled in the kernel and a current version of iproute2 is included. The netem kernel component is enabled under:
Networking -->
Networking Options -->
QoS and/or fair queuing -->
Network emulator

As I know, the latest gentoo is based on 2.6.15 distribution whose netem should already be enabled. Can any one give me some idea about how to use the netem under gentoo, or how to enable the netem kernel component in it (the description in home page is not very clear).

[jiang20]

netem in current kernel 2.6.15 gentoo is disabled. so i recompile the kernel then it works properly.