From 636cc9a9188f84085873bf9e9ca18946e4b7cbac Mon Sep 17 00:00:00 2001 From: Keisuke Nishimura Date: Wed, 10 Jan 2024 14:17:06 +0100 Subject: [PATCH] sched/fair: Take the scheduling domain into account in select_idle_smt() BugLink: https://bugs.launchpad.net/bugs/2060097 [ Upstream commit 8aeaffef8c6eceab0e1498486fdd4f3dc3b7066c ] When picking a CPU on task wakeup, select_idle_smt() has to take into account the scheduling domain of @target. This is because the "isolcpus" kernel command line option can remove CPUs from the domain to isolate them from other SMT siblings. This fix checks if the candidate CPU is in the target scheduling domain. Commit: df3cb4ea1fb6 ("sched/fair: Fix wrong cpu selecting from isolated domain") ... originally introduced this fix by adding the check of the scheduling domain in the loop. However, commit: 3e6efe87cd5cc ("sched/fair: Remove redundant check in select_idle_smt()") ... accidentally removed the check. Bring it back. Fixes: 3e6efe87cd5c ("sched/fair: Remove redundant check in select_idle_smt()") Signed-off-by: Keisuke Nishimura Signed-off-by: Julia Lawall Signed-off-by: Ingo Molnar Reviewed-by: Vincent Guittot Link: https://lore.kernel.org/r/20240110131707.437301-1-keisuke.nishimura@inria.fr Signed-off-by: Sasha Levin (cherry picked from commit 9897b7432572f2faa5440d2a2922822a8819fee2) Signed-off-by: Paolo Pisati --- kernel/sched/fair.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 533547e3c90a..66457d4b8965 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7311,13 +7311,19 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu /* * Scan the local SMT mask for idle CPUs. */ -static int select_idle_smt(struct task_struct *p, int target) +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) { int cpu; for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) { if (cpu == target) continue; + /* + * Check if the CPU is in the LLC scheduling domain of @target. + * Due to isolcpus, there is no guarantee that all the siblings are in the domain. + */ + if (!cpumask_test_cpu(cpu, sched_domain_span(sd))) + continue; if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) return cpu; } @@ -7341,7 +7347,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma return __select_idle_cpu(core, p); } -static inline int select_idle_smt(struct task_struct *p, int target) +static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) { return -1; } @@ -7591,7 +7597,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) has_idle_core = test_idle_cores(target); if (!has_idle_core && cpus_share_cache(prev, target)) { - i = select_idle_smt(p, prev); + i = select_idle_smt(p, sd, prev); if ((unsigned int)i < nr_cpumask_bits) return i; }