just to add that running 2.6.32-25-generic #43-Ubuntu SMP Wed Sep 1 09:46:39 UTC 2010 i686 GNU/Linux, if I boot without "nohz=off" I get error messages like in https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/586243?comments=all:

ep  7 23:26:54 mick-laptop kernel: [  347.754343] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(0).
Sep  7 23:26:54 mick-laptop kernel: [  347.754346] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.754376] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(1).
Sep  7 23:26:54 mick-laptop kernel: [  347.754379] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.765791] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(2).
Sep  7 23:26:54 mick-laptop kernel: [  347.765794] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.766126] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(3).
Sep  7 23:26:54 mick-laptop kernel: [  347.766129] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.766866] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(4).
Sep  7 23:26:54 mick-laptop kernel: [  347.766870] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.769669] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(5).
Sep  7 23:26:54 mick-laptop kernel: [  347.769673] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.769704] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(6).
Sep  7 23:26:54 mick-laptop kernel: [  347.769706] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.781450] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(7).
Sep  7 23:26:54 mick-laptop kernel: [  347.781454] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.784999] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(8).
Sep  7 23:26:54 mick-laptop kernel: [  347.785003] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.785033] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(9).
Sep  7 23:26:54 mick-laptop kernel: [  347.785036] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.797480] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(10).
Sep  7 23:26:54 mick-laptop kernel: [  347.797484] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.797860] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(11).
Sep  7 23:26:54 mick-laptop kernel: [  347.797863] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.798597] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(12).
Sep  7 23:26:54 mick-laptop kernel: [  347.798601] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.800341] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(13).
Sep  7 23:26:54 mick-laptop kernel: [  347.800344] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.800375] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(14).
Sep  7 23:26:54 mick-laptop kernel: [  347.800377] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.813134] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(15).
Sep  7 23:26:54 mick-laptop kernel: [  347.813137] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.815725] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(0).
Sep  7 23:26:54 mick-laptop kernel: [  347.815729] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !
Sep  7 23:26:54 mick-laptop kernel: [  347.815759] [drm:radeon_ib_schedule] *ERROR* radeon: couldn't schedule IB(1).
Sep  7 23:26:54 mick-laptop kernel: [  347.815761] [drm:radeon_cs_ioctl] *ERROR* Faild to schedule IB !