sched/eas: Don't update misfit status if the task is pinned

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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Quentin Perret <[email protected]>
Acked-by: Valentin Schneider <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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