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Message-ID: <b5e454a8-6533-446b-9546-37fc63e9089e@linux.ibm.com>
Date: Fri, 4 Jul 2025 01:15:35 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Tim Chen <tim.c.chen@...ux.intel.com>, Chen Yu <yu.c.chen@...el.com>
Cc: Juri Lelli <juri.lelli@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
Tim Chen <tim.c.chen@...el.com>,
Vincent Guittot
<vincent.guittot@...aro.org>,
Libo Chen <libo.chen@...cle.com>, Abel Wu <wuyun.abel@...edance.com>,
Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
Hillf Danton <hdanton@...a.com>, Len Brown <len.brown@...el.com>,
linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
K Prateek Nayak <kprateek.nayak@....com>,
"Gautham R . Shenoy" <gautham.shenoy@....com>
Subject: Re: [RFC patch v3 10/20] sched: Calculate the number of tasks that
have LLC preference on a runqueue
On 6/18/25 23:57, Tim Chen wrote:
> Track for each run queue, the number of tasks that have a LLC preference
> and how many of those tasks are running in its preferred LLC. This is
> similar to nr_numa_running and nr_preferred_running for NUMA balance,
> and will be used by the cache-aware load balancing in subsequent patches.
>
> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
> ---
> kernel/sched/core.c | 12 ++++++++++++
> kernel/sched/fair.c | 42 +++++++++++++++++++++++++++++++++++++++++-
> kernel/sched/sched.h | 7 +++++++
> 3 files changed, 60 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d9c3e75f79d1..34056eb79ef2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -498,6 +498,18 @@ void __trace_set_current_state(int state_value)
> }
> EXPORT_SYMBOL(__trace_set_current_state);
>
> +#ifdef CONFIG_SMP
CONFIG_SMP is true unconditionally now. Else may need to go.
> +int task_llc(const struct task_struct *p)
> +{
> + return per_cpu(sd_llc_id, task_cpu(p));
> +}
> +#else
> +int task_llc(const struct task_struct *p)
> +{
> + return 0;
> +}
> +#endif
> +
> /*
> * Serialization rules:
> *
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index cc804a8c7061..88ff47194faa 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1195,6 +1195,18 @@ static inline int llc_idx(int cpu)
> return per_cpu(sd_llc_idx, cpu);
> }
>
> +static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
> +{
> + rq->nr_llc_running += (p->preferred_llc != -1);
> + rq->nr_pref_llc_running += (p->preferred_llc == task_llc(p));
> +}
> +
> +static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
> +{
> + rq->nr_llc_running -= (p->preferred_llc != -1);
> + rq->nr_pref_llc_running -= (p->preferred_llc == task_llc(p));
> +}
> +
> void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
> {
> unsigned long epoch;
> @@ -1298,8 +1310,11 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
> if (mm->mm_sched_cpu != -1)
> mm_sched_llc = per_cpu(sd_llc_id, mm->mm_sched_cpu);
>
> - if (p->preferred_llc != mm_sched_llc)
> + if (p->preferred_llc != mm_sched_llc) {
> + account_llc_dequeue(rq, p);
> p->preferred_llc = mm_sched_llc;
> + account_llc_enqueue(rq, p);
> + }
> }
>
> static void task_tick_cache(struct rq *rq, struct task_struct *p)
> @@ -1400,6 +1415,14 @@ void init_sched_mm(struct task_struct *p)
> work->next = work;
> }
>
> +void reset_llc_stats(struct rq *rq)
> +{
> + if (rq->nr_llc_running)
> + rq->nr_llc_running = 0;
> +
> + rq->nr_pref_llc_running = 0;
> +}
> +
> #else
>
> static inline void account_mm_sched(struct rq *rq, struct task_struct *p,
> @@ -1410,6 +1433,17 @@ void init_sched_mm(struct task_struct *p) { }
>
> static void task_tick_cache(struct rq *rq, struct task_struct *p) { }
>
> +static void account_llc_enqueue(struct rq *rq, struct task_struct *p)
> +{
> +}
> +
> +static void account_llc_dequeue(struct rq *rq, struct task_struct *p)
> +{
> +}
> +
> +void reset_llc_stats(struct rq *rq)
> +{
> +}
> #endif
>
> static inline
> @@ -3939,6 +3973,7 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
> struct rq *rq = rq_of(cfs_rq);
>
> account_numa_enqueue(rq, task_of(se));
> + account_llc_enqueue(rq, task_of(se));
> list_add(&se->group_node, &rq->cfs_tasks);
> }
> #endif
> @@ -3952,10 +3987,15 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
> #ifdef CONFIG_SMP
> if (entity_is_task(se)) {
> account_numa_dequeue(rq_of(cfs_rq), task_of(se));
> + account_llc_dequeue(rq_of(cfs_rq), task_of(se));
> list_del_init(&se->group_node);
> }
> #endif
> cfs_rq->nr_queued--;
> +
> + /* safeguard? */
> + if (!parent_entity(se) && !cfs_rq->nr_queued)
> + reset_llc_stats(rq_of(cfs_rq));
> }
>
> /*
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 74eb2f3615aa..6c83a71ac8ca 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1104,6 +1104,10 @@ struct rq {
> unsigned int nr_preferred_running;
> unsigned int numa_migrate_on;
> #endif
> +#ifdef CONFIG_SCHED_CACHE
> + unsigned int nr_pref_llc_running;
> + unsigned int nr_llc_running;
> +#endif
> #ifdef CONFIG_NO_HZ_COMMON
> #ifdef CONFIG_SMP
> unsigned long last_blocked_load_update_tick;
> @@ -1948,6 +1952,9 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
>
> #endif /* !CONFIG_NUMA_BALANCING */
>
> +extern void reset_llc_stats(struct rq *rq);
> +extern int task_llc(const struct task_struct *p);
> +
> #ifdef CONFIG_SMP
>
> static inline void
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