diff options
| author | K Prateek Nayak <kprateek.nayak@amd.com> | 2026-03-12 04:44:34 +0000 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-03-18 09:06:50 +0100 |
| commit | fe7171d0d5dfbe189e41db99580ebacafc3c09ce (patch) | |
| tree | c0c4e22bd26262c7565be34f647e95bfb4006b18 /kernel | |
| parent | f1320a8dd8ba6518ddb53ea4e3efcb49dc41d257 (diff) | |
sched/fair: Simplify SIS_UTIL handling in select_idle_cpu()
Use the "sd_llc" passed to select_idle_cpu() to obtain the
"sd_llc_shared" instead of dereferencing the per-CPU variable.
Since "sd->shared" is always reclaimed at the same time as "sd" via
call_rcu() and update_top_cache_domain() always ensures a valid
"sd->shared" assignment when "sd_llc" is present, "sd_llc->shared" can
always be dereferenced without needing an additional check.
While at it move the cpumask_and() operation after the SIS_UTIL bailout
check to avoid unnecessarily computing the cpumask.
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://patch.msgid.link/20260312044434.1974-10-kprateek.nayak@amd.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/fair.c | 27 |
1 files changed, 16 insertions, 11 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 85c22f0f8de8..0a35a82e4792 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7876,21 +7876,26 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool { struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask); int i, cpu, idle_cpu = -1, nr = INT_MAX; - struct sched_domain_shared *sd_share; - - cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); if (sched_feat(SIS_UTIL)) { - sd_share = rcu_dereference_all(per_cpu(sd_llc_shared, target)); - if (sd_share) { - /* because !--nr is the condition to stop scan */ - nr = READ_ONCE(sd_share->nr_idle_scan) + 1; - /* overloaded LLC is unlikely to have idle cpu/core */ - if (nr == 1) - return -1; - } + /* + * Increment because !--nr is the condition to stop scan. + * + * Since "sd" is "sd_llc" for target CPU dereferenced in the + * caller, it is safe to directly dereference "sd->shared". + * Topology bits always ensure it assigned for "sd_llc" abd it + * cannot disappear as long as we have a RCU protected + * reference to one the associated "sd" here. + */ + nr = READ_ONCE(sd->shared->nr_idle_scan) + 1; + /* overloaded LLC is unlikely to have idle cpu/core */ + if (nr == 1) + return -1; } + if (!cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr)) + return -1; + if (static_branch_unlikely(&sched_cluster_active)) { struct sched_group *sg = sd->groups; |