Although idle load balancing obviously only concern idle CPUs, it can be a disturbance on a busy nohz_full CPU. Indeed a CPU can only get rid of an idle load balancing duty once a tick fires while it runs a task and this can take a while in a nohz_full CPU.
We could fix that and escape the idle load balancing duty from the very idle exit path but that would bring unecessary overhead. Lets just not bother and leave that job to housekeeping CPUs (those outside nohz_full range). The nohz_full CPUs simply don't want any disturbance. Signed-off-by: Frederic Weisbecker <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Peter Zijlstra <[email protected]> --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d711093..cfca960 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8659,6 +8659,10 @@ void nohz_balance_enter_idle(int cpu) if (!cpu_active(cpu)) return; + /* Spare idle load balancing on CPUs that don't want to be disturbed */ + if (!is_housekeeping_cpu(cpu)) + return; + if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu))) return; -- 2.7.4
