linux-kernel - [RFC patch v3 09/20] sched: Introduce task preferred LLC field

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Message-Id: <7b9df4433d73ce415a27925ce42cec53774debaf.1750268218.git.tim.c.chen@linux.intel.com>
Date: Wed, 18 Jun 2025 11:27:57 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>,
	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,
	Chen Yu <yu.c.chen@...el.com>
Subject: [RFC patch v3 09/20] sched: Introduce task preferred LLC field

With cache aware scheduling enabled, each process is assigned
a preferred LLC id, which will be used to quickly identify
the LLC domain this thread prefers to run. This is similar to
numa_preferred_nid for NUMA balance.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---
 include/linux/sched.h | 1 +
 init/init_task.c      | 3 +++
 kernel/sched/fair.c   | 7 +++++++
 3 files changed, 11 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7ce95a32e9ff..2f1cb7445733 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1404,6 +1404,7 @@ struct task_struct {
 
 #ifdef CONFIG_SCHED_CACHE
 	struct callback_head		cache_work;
+	int				preferred_llc;
 #endif
 
 #ifdef CONFIG_RSEQ
diff --git a/init/init_task.c b/init/init_task.c
index e557f622bd90..5fffbe766f57 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -188,6 +188,9 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 	.numa_group	= NULL,
 	.numa_faults	= NULL,
 #endif
+#ifdef CONFIG_SCHED_CACHE
+	.preferred_llc  = -1,
+#endif
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 	.kasan_depth	= 1,
 #endif
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5549710d95cf..cc804a8c7061 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1267,6 +1267,7 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 	struct mm_struct *mm = p->mm;
 	struct mm_sched *pcpu_sched;
 	unsigned long epoch;
+	int mm_sched_llc = -1;
 
 	/*
 	 * init_task and kthreads don't be having no mm
@@ -1293,6 +1294,12 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec)
 		mm->mm_sched_cpu = -1;
 		pcpu_sched->occ = 0;
 	}
+
+	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)
+		p->preferred_llc = mm_sched_llc;
 }
 
 static void task_tick_cache(struct rq *rq, struct task_struct *p)
-- 
2.32.0