diff options
| author | Keisuke Nishimura <keisuke.nishimura@inria.fr> | 2023-10-31 14:38:22 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-11-14 22:27:01 +0100 |
| commit | 6d7e4782bcf549221b4ccfffec2cf4d1a473f1a3 (patch) | |
| tree | fec2d1d9b8e4c1c2f5fb3e0a9255e016c93ba5b3 | |
| parent | 8b39d20eceeda6c4eb23df1497f9ed2fffdc8f69 (diff) | |
| download | linux-rcu-6d7e4782bcf549221b4ccfffec2cf4d1a473f1a3.tar.gz | |
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
| -rw-r--r-- | kernel/sched/fair.c | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 025d90925bf631..d7a3c63a2171a8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11184,12 +11184,16 @@ static int should_we_balance(struct lb_env *env) continue; } - /* Are we the first idle CPU? */ + /* + * Are we the first idle core in a non-SMT domain or higher, + * or the first idle CPU in a SMT domain? + */ return cpu == env->dst_cpu; } - if (idle_smt == env->dst_cpu) - return true; + /* Are we the first idle CPU with busy siblings? */ + if (idle_smt != -1) + return idle_smt == env->dst_cpu; /* Are we the first CPU of this group ? */ return group_balance_cpu(sg) == env->dst_cpu; |