This is a note to let you know that I've just added the patch titled sched/eas: Don't update misfit status if the task is pinned to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-eas-don-t-update-misfit-status-if-the-task-is-.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 1a8030b4dd44ed4ba5d48457fda6d1a04d5bad4e Author: Qais Yousef <qais.yousef@xxxxxxx> Date: Tue Jan 19 12:07:55 2021 +0000 sched/eas: Don't update misfit status if the task is pinned [ Upstream commit 0ae78eec8aa64e645866e75005162603a77a0f49 ] If the task is pinned to a cpu, setting the misfit status means that we'll unnecessarily continuously attempt to migrate the task but fail. This continuous failure will cause the balance_interval to increase to a high value, and eventually cause unnecessary significant delays in balancing the system when real imbalance happens. Caught while testing uclamp where rt-app calibration loop was pinned to cpu 0, shortly after which we spawn another task with high util_clamp value. The task was failing to migrate after over 40ms of runtime due to balance_interval unnecessary expanded to a very high value from the calibration loop. Not done here, but it could be useful to extend the check for pinning to verify that the affinity of the task has a cpu that fits. We could end up in a similar situation otherwise. Fixes: 3b1baa6496e6 ("sched/fair: Add 'group_misfit_task' load-balance type") Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Quentin Perret <qperret@xxxxxxxxxx> Acked-by: Valentin Schneider <valentin.schneider@xxxxxxx> Link: https://lkml.kernel.org/r/20210119120755.2425264-1-qais.yousef@xxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3dd7c10d6a582..611adca1e6d0c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3814,7 +3814,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq) if (!static_branch_unlikely(&sched_asym_cpucapacity)) return; - if (!p) { + if (!p || p->nr_cpus_allowed == 1) { rq->misfit_task_load = 0; return; }