entry,hrtimer: Push reprogramming timers into the interrupt return path
Currently hrtimer_interrupt() runs expired timers, which can re-arm
themselves, after which it computes the next expiration time and
re-programs the hardware.
However, things like HRTICK, a highres timer driving preemption,
cannot re-arm itself at the point of running, since the next task has
not been determined yet. The schedule() in the interrupt return path
will switch to the next task, which then causes a new hrtimer to be
programmed.
This then results in reprogramming the hardware at least twice, once
after running the timers, and once upon selecting the new task.
Notably, *both* events happen in the interrupt.
By pushing the hrtimer reprogram all the way into the interrupt return
path, it runs after schedule() and this double reprogram can be
avoided.
XXX: 0-day is unhappy with this patch -- it is reporting lockups that
very much look like a timer goes missing. Am unable to reproduce.
Notable: the lockup goes away when the workloads are ran without perf
monitors.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
6 files changed
