sched/fair: Fix the decision for load balance
authorKeisuke Nishimura <keisuke.nishimura@inria.fr>
Tue, 31 Oct 2023 13:38:22 +0000 (14:38 +0100)
committerPeter Zijlstra <peterz@infradead.org>
Tue, 14 Nov 2023 21:27:01 +0000 (22:27 +0100)
commit6d7e4782bcf549221b4ccfffec2cf4d1a473f1a3
treefec2d1d9b8e4c1c2f5fb3e0a9255e016c93ba5b3
parent8b39d20eceeda6c4eb23df1497f9ed2fffdc8f69
sched/fair: Fix the decision for load balance

should_we_balance is called for the decision to do load-balancing.
When sched ticks invoke this function, only one CPU should return
true. However, in the current code, two CPUs can return true. The
following situation, where b means busy and i means idle, is an
example, because CPU 0 and CPU 2 return true.

        [0, 1] [2, 3]
         b  b   i  b

This fix checks if there exists an idle CPU with busy sibling(s)
after looking for a CPU on an idle core. If some idle CPUs with busy
siblings are found, just the first one should do load-balancing.

Fixes: b1bfeab9b002 ("sched/fair: Consider the idle state of the whole core for load balance")
Signed-off-by: Keisuke Nishimura <keisuke.nishimura@inria.fr>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20231031133821.1570861-1-keisuke.nishimura@inria.fr
kernel/sched/fair.c