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sched/cache: Count tasks prefering destination LLC in a sched group

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During LLC load balancing, tabulate the number of tasks on each runqueue
that prefer the LLC contains the env->dst_cpu in a sched group.

For example, consider a system with 4 LLC sched groups (LLC0 to LLC3)
balancing towards LLC3. LLC0 has 3 tasks preferring LLC3, LLC1 has
2, and LLC2 has 1. LLC0, having the most tasks preferring LLC3, is
selected as the busiest source to pick tasks from.

Within a source LLC, the total number of tasks preferring a destination
LLC is computed by summing counts across all CPUs in that LLC. For
instance, if LLC0 has CPU0 with 2 tasks and CPU1 with 1 task preferring
LLC3, the total for LLC0 is 3.

These statistics allow the load balancer to choose tasks from source
sched groups that best match their preferred LLCs.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/3d8502a33a753c4384b368f97f64ee70b1cea0db.1775065312.git.tim.c.chen@linux.intel.com
This commit is contained in:
Tim Chen 2026-04-01 14:52:22 -07:00 committed by Peter Zijlstra
parent 82c960aee3
commit 15ad45fb80
1 changed files with 17 additions and 0 deletions
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17
kernel/sched/fair.c
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@ -10834,6 +10834,9 @@ struct sg_lb_stats {
unsigned int nr_numa_running;
unsigned int nr_preferred_running;
#endif
#ifdef CONFIG_SCHED_CACHE
unsigned int nr_pref_dst_llc;
#endif
};
/*
@ -11328,6 +11331,20 @@ static inline void update_sg_lb_stats(struct lb_env *env,
if (cpu_overutilized(i))
sgs->group_overutilized = 1;
#ifdef CONFIG_SCHED_CACHE
if (sched_cache_enabled()) {
struct sched_domain *sd_tmp;
int dst_llc;
dst_llc = llc_id(env->dst_cpu);
if (llc_id(i) != dst_llc) {
sd_tmp = rcu_dereference_all(rq->sd);
if (sd_tmp && (unsigned int)dst_llc < sd_tmp->llc_max)
sgs->nr_pref_dst_llc += sd_tmp->llc_counts[dst_llc];
}
}
#endif
/*
* No need to call idle_cpu() if nr_running is not 0
*/