linux-kernel - [RFC PATCH v3 1/3] sched/isolation: Add infrastructure for dynamic CPU isolation

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Message-ID: <20240916122044.3056787-2-costa.shul@redhat.com>
Date: Mon, 16 Sep 2024 15:20:42 +0300
From: Costa Shulyupin <costa.shul@...hat.com>
To: longman@...hat.com,
	ming.lei@...hat.com,
	pauld@...hat.com,
	juri.lelli@...hat.com,
	vschneid@...hat.com,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Zefan Li <lizefan.x@...edance.com>,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Costa Shulyupin <costa.shul@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: [RFC PATCH v3 1/3] sched/isolation: Add infrastructure for dynamic CPU isolation

Introduce infrastructure function housekeeping_update() to change
housekeeping_cpumask during runtime and adjust configurations of depended
subsystems.

Configuration adjustments of subsystems follow in subsequent patches.

Parent patch:
sched/isolation: Exclude dynamically isolated CPUs from housekeeping masks
https://lore.kernel.org/lkml/20240821142312.236970-1-longman@redhat.com/

Signed-off-by: Costa Shulyupin <costa.shul@...hat.com>

---
Changes in v2:
- remove unnecessary `err` variable
- add for_each_clear_bit... to clear isolated CPUs
- Address Gleixner's comments:
- use WRITE_ONCE to change housekeeping.flags
- use `struct cpumask *update` in signature of housekeeping_update

v1:
- https://lore.kernel.org/lkml/20240516190437.3545310-2-costa.shul@redhat.com/
---
 kernel/sched/isolation.c | 38 +++++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 3018ba81eb65d..3f24921b929a0 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -124,6 +124,36 @@ static void __init housekeeping_setup_type(enum hk_type type,
 		     housekeeping_staging);
 }
 
+/*
+ * housekeeping_update - change housekeeping.cpumasks[type] and propagate the
+ * change.
+ */
+static int housekeeping_update(enum hk_type type, const struct cpumask *update)
+{
+	struct {
+		struct cpumask changed;
+		struct cpumask enable;
+		struct cpumask disable;
+	} *masks;
+
+	masks = kmalloc(sizeof(*masks), GFP_KERNEL);
+	if (!masks)
+		return -ENOMEM;
+
+	lockdep_assert_cpus_held();
+	cpumask_xor(&masks->changed, housekeeping_cpumask(type), update);
+	cpumask_and(&masks->enable, &masks->changed, update);
+	cpumask_andnot(&masks->disable, &masks->changed, update);
+	cpumask_copy(housekeeping.cpumasks[type], update);
+	WRITE_ONCE(housekeeping.flags, housekeeping.flags | BIT(type));
+	if (!static_branch_unlikely(&housekeeping_overridden))
+		static_key_enable_cpuslocked(&housekeeping_overridden.key);
+
+	kfree(masks);
+
+	return 0;
+}
+
 static int __init housekeeping_setup(char *str, unsigned long flags)
 {
 	cpumask_var_t non_housekeeping_mask, housekeeping_staging;
@@ -327,8 +357,11 @@ int housekeeping_exlude_isolcpus(const struct cpumask *isolcpus, unsigned long f
 		/*
 		 * Reset housekeeping to bootup default
 		 */
+
+		for_each_clear_bit(type, &boot_hk_flags, HK_TYPE_MAX)
+			housekeeping_update(type, cpu_possible_mask);
 		for_each_set_bit(type, &boot_hk_flags, HK_TYPE_MAX)
-			cpumask_copy(housekeeping.cpumasks[type], boot_hk_cpumask);
+			housekeeping_update(type, boot_hk_cpumask);
 
 		WRITE_ONCE(housekeeping.flags, boot_hk_flags);
 		if (!boot_hk_flags && static_key_enabled(&housekeeping_overridden))
@@ -355,9 +388,8 @@ int housekeeping_exlude_isolcpus(const struct cpumask *isolcpus, unsigned long f
 		cpumask_andnot(tmp_mask, src_mask, isolcpus);
 		if (!cpumask_intersects(tmp_mask, cpu_online_mask))
 			return -EINVAL;	/* Invalid isolated CPUs */
-		cpumask_copy(housekeeping.cpumasks[type], tmp_mask);
+		housekeeping_update(type, tmp_mask);
 	}
-	WRITE_ONCE(housekeeping.flags, boot_hk_flags | flags);
 	excluded = true;
 	if (!static_key_enabled(&housekeeping_overridden))
 		static_key_enable_cpuslocked(&housekeeping_overridden.key);
-- 
2.45.0