linux-kernel - [RFC patch v3 08/20] sched: Set up LLC indexing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <71e251a086be786fb2a0480bbab69142d14bd22d.1750268218.git.tim.c.chen@linux.intel.com>
Date: Wed, 18 Jun 2025 11:27:56 -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 08/20] sched: Set up LLC indexing

Prepare for indexing arrays that track in each run queue: the number
of tasks preferring current LLC and each of the other LLC.

The reason to introduce LLC index is because the per LLC-scope data
is needed to do cache aware load balancing. However, the native lld_id
is usually the first CPU of that LLC domain, which is not continuous,
which might waste the space if the per LLC-scope data is stored
in an array (in current implementation).

In the future, this LLC index could be removed after
the native llc_id is used as the key to search into xarray based
array.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---
 include/linux/sched.h   |  3 +++
 kernel/sched/fair.c     | 12 ++++++++++++
 kernel/sched/sched.h    |  2 ++
 kernel/sched/topology.c | 29 +++++++++++++++++++++++++++++
 4 files changed, 46 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d0e4cda2b3cd..7ce95a32e9ff 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -810,6 +810,9 @@ struct kmap_ctrl {
 #endif
 };
 
+/* XXX need fix to not use magic number */
+#define MAX_LLC 64
+
 struct task_struct {
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 	/*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 10ea408d0e40..5549710d95cf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1183,6 +1183,18 @@ static int llc_id(int cpu)
 	return per_cpu(sd_llc_id, cpu);
 }
 
+/*
+ * continous index.
+ * TBD: replace by xarray with key llc_id()
+ */
+static inline int llc_idx(int cpu)
+{
+	if (cpu < 0)
+		return -1;
+
+	return per_cpu(sd_llc_idx, cpu);
+}
+
 void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1c6fd45c7f62..74eb2f3615aa 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2037,6 +2037,7 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DECLARE_PER_CPU(int, sd_llc_size);
 DECLARE_PER_CPU(int, sd_llc_id);
+DECLARE_PER_CPU(int, sd_llc_idx);
 DECLARE_PER_CPU(int, sd_share_id);
 DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
@@ -2045,6 +2046,7 @@ DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
 
 extern struct static_key_false sched_asym_cpucapacity;
 extern struct static_key_false sched_cluster_active;
+extern int max_llcs;
 
 static __always_inline bool sched_asym_cpucap_active(void)
 {
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index f1ebc60d967f..b7bb13045dd8 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -672,6 +672,7 @@ static void destroy_sched_domains(struct sched_domain *sd)
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DEFINE_PER_CPU(int, sd_llc_size);
 DEFINE_PER_CPU(int, sd_llc_id);
+DEFINE_PER_CPU(int, sd_llc_idx);
 DEFINE_PER_CPU(int, sd_share_id);
 DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
 DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
@@ -681,6 +682,25 @@ DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
 DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
 DEFINE_STATIC_KEY_FALSE(sched_cluster_active);
 
+int max_llcs = -1;
+
+static void update_llc_idx(int cpu)
+{
+#ifdef CONFIG_SCHED_CACHE
+	int idx = -1, llc_id = -1;
+
+	llc_id = per_cpu(sd_llc_id, cpu);
+	idx = per_cpu(sd_llc_idx, llc_id);
+
+	if (idx < 0) {
+		idx = max_llcs++;
+		BUG_ON(idx > MAX_LLC);
+		per_cpu(sd_llc_idx, llc_id) = idx;
+	}
+	per_cpu(sd_llc_idx, cpu) = idx;
+#endif
+}
+
 static void update_top_cache_domain(int cpu)
 {
 	struct sched_domain_shared *sds = NULL;
@@ -699,6 +719,7 @@ static void update_top_cache_domain(int cpu)
 	per_cpu(sd_llc_size, cpu) = size;
 	per_cpu(sd_llc_id, cpu) = id;
 	rcu_assign_pointer(per_cpu(sd_llc_shared, cpu), sds);
+	update_llc_idx(cpu);
 
 	sd = lowest_flag_domain(cpu, SD_CLUSTER);
 	if (sd)
@@ -2394,6 +2415,14 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
 	bool has_asym = false;
 	bool has_cluster = false;
 
+#ifdef CONFIG_SCHED_CACHE
+	if (max_llcs < 0) {
+		for_each_possible_cpu(i)
+			per_cpu(sd_llc_idx, i) = -1;
+		max_llcs = 0;
+	}
+#endif
+
 	if (WARN_ON(cpumask_empty(cpu_map)))
 		goto error;
 
-- 
2.32.0