From: Keisuke Nishimura <keisuke.nishimura@inria.fr> stable inclusion from stable-v6.6.4 commit 47a3075109978d9684f7fea59de7c639fcba7145 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8N1WC Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 6d7e4782bcf549221b4ccfffec2cf4d1a473f1a3 ] 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.f... Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com> --- kernel/sched/fair.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8ff7ddc2f74a..63827e26c1f8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11121,12 +11121,16 @@ 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; -- 2.20.1