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sched/cache: Calculate the percpu sd task LLC preference

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Calculate the number of tasks' LLC preferences for each runqueue.
This statistic is computed during task enqueue and dequeue
operations, and is used by the cache-aware load balancing.

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/d15a64436d3acd19c5c53344c5e9d3d0b79b3233.1775065312.git.tim.c.chen@linux.intel.com
This commit is contained in:
Tim Chen 2026-04-01 14:52:21 -07:00 committed by Peter Zijlstra
parent a8d0ca0b7f
commit 82c960aee3
1 changed files with 24 additions and 0 deletions
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24
kernel/sched/fair.c
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@ -1386,6 +1386,7 @@ static int llc_id(int cpu)
static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
{
struct sched_domain *sd;
int pref_llc;
pref_llc = p->preferred_llc;
@ -1394,10 +1395,15 @@ static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
rq->nr_llc_running++;
rq->nr_pref_llc_running += (pref_llc == task_llc(p));
sd = rcu_dereference_all(rq->sd);
if (sd && (unsigned int)pref_llc < sd->llc_max)
sd->llc_counts[pref_llc]++;
}
static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
{
struct sched_domain *sd;
int pref_llc;
pref_llc = p->preferred_llc;
@ -1406,6 +1412,24 @@ static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
rq->nr_llc_running--;
rq->nr_pref_llc_running -= (pref_llc == task_llc(p));
sd = rcu_dereference_all(rq->sd);
if (sd && (unsigned int)pref_llc < sd->llc_max) {
/*
* There is a race condition between dequeue
* and CPU hotplug. After a task has been enqueued
* on CPUx, a CPU hotplug event occurs, and all online
* CPUs (including CPUx) rebuild their sched_domains
* and reset statistics to zero(including sd->llc_counts).
* This can cause temporary undercount and we have to
* check for such underflow in sd->llc_counts.
*
* This undercount is temporary and accurate accounting
* will resume once the rq has a chance to be idle.
*/
if (sd->llc_counts[pref_llc])
sd->llc_counts[pref_llc]--;
}
}
void mm_init_sched(struct mm_struct *mm,