Why do I need hyper-thread aware batch scheduling?
If you have a hyperthread (P4HT) processor and run it as two logical cpus you can have a very low priority task running that can consume 50% of your physical cpu's capacity no matter how high priority tasks you are running. For example if you use the distributed computing client setiathome you will be effectively be running at half your cpu's speed even if you run setiathome at nice 20. Batch scheduling for normal cpus allows only idle time to be used for batch tasks, and for HT cpus only allows idle time when both logical cpus are idle.
BTW this is going to be an issue even on normal (non-HT)
systems. Imagine memory-bound scientific task on CPU0 and nice -20
memory-bound seti&home at CPU1. Even without hyperthreading, your
scientific task is going to run at 50% of speed and seti&home is going
to get second half. Oops.