Severe sluggishness under 'nice' load in 2.6.24 kernels

I usually run two instances of folding@home, using schedtool to assign each to a different CPU core, and both to nice +19 and SCHED_IDLEPRIO.

Since booting the 2.6.24 -generic kernels, my system has become severely sluggish -- it will take somewhere between 1/4 and 1/2 second (subjectively) for a character to appear on-screen after hitting the key. This happens with both Metacity and Compiz-Fusion (using git version). Switching to the NV driver reduces this sluggishness slightly, but it's still subjectively worse than the 2.6.22 kernel ever was at its worst.

Stopping my 'niced' folding@home processes immediately alleviates this severe sluggishness, so it seems that somehow these 'nice' tasks are being given a too high priority. I believe this most likely has something to do with the new CFS scheduler in the 2.6.24 kernel.

I tried to reproduce this using a simple busy loop in bash, and with 'yes', and by using cat /dev/zero or cat /dev/urandom > /dev/null, each niced to +19 and SCHED_IDLEPRIO, but for some reason, these did not create the same sluggishness that folding@home creates. In addition, these loads did not show up as 'nice' in my Gnome system monitor panel applet, and they also sped up my CPU despite cpufreq being set to ignore 'nice' loads. Instead, these processes showed up as 'system' load.