Patch "sched/eas: Don't update misfit status if the task is pinned" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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;
 	}