On Tue, Jan 14, 2025 at 01:29:04PM +0000, Christian Loehle wrote: > I know nothing about bcachefs internals, but could this also be a problem? > The rebalance thread might not run for O(second) or so?
SCHED_BATCH should not behave anything like that, mostly SCHED_BATCH tasks will not cause wakeup preemption. But otherwise they compete at the same level as everybody else. Notably a BATCH and NORMAL task that are each while(1) loops will get the normal 50-50 distribution of time. It's just that when a NORMAL task is running, the waking of a BATCH task won't ever kick the NORMAL from the CPU, instead waiting for the tick to do so. So a task that is IO heavy (as suggested here), that wakes a lot to issue further IO, will not immediately interrupt whatever is on the CPU, instead it waits until it gets selected through other means.
