[PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[James Morse]

When a CPU is taken offline resctrl may need to move the overflow or
limbo handlers to run on a different CPU.

Once the offline callbacks have been split, cqm_setup_limbo_handler()
will be called while the CPU that is going offline is still present
in the cpu_mask.

Pass the CPU to exclude to cqm_setup_limbo_handler() and
mbm_setup_overflow_handler(). These functions can use a variant of
cpumask_any_but() when selecting the CPU. -1 is used to indicate no CPUs
need excluding.

A subsequent patch moves these calls to be before CPUs have been removed,
so this exclude_cpus behaviour is temporary.

Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
---
Changes since v2:
 * Rephrased a comment to avoid a two letter bad-word. (we)
 * Avoid assigning mbm_work_cpu if the domain is going to be free()d
 * Added cpumask_any_housekeeping_but(), I dislike the name

Changes since v3:
 * Marked an explanatory comment as temporary as the subsequent patch is
   no longer adjacent.
---
 arch/x86/kernel/cpu/resctrl/core.c     |  8 +++--
 arch/x86/kernel/cpu/resctrl/internal.h | 37 +++++++++++++++++++++--
 arch/x86/kernel/cpu/resctrl/monitor.c  | 42 +++++++++++++++++++++-----
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  6 ++--
 include/linux/resctrl.h                |  3 ++
 5 files changed, 82 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index e00f3542e60e..187ed127a446 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -582,12 +582,16 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 	if (r == &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl) {
 		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
 			cancel_delayed_work(&d->mbm_over);
-			mbm_setup_overflow_handler(d, 0);
+			/*
+			 * temporary: exclude_cpu=-1 as this CPU has already
+			 * been removed by cpumask_clear_cpu()d
+			 */
+			mbm_setup_overflow_handler(d, 0, RESCTRL_PICK_ANY_CPU);
 		}
 		if (is_llc_occupancy_enabled() && cpu == d->cqm_work_cpu &&
 		    has_busy_rmid(r, d)) {
 			cancel_delayed_work(&d->cqm_limbo);
-			cqm_setup_limbo_handler(d, 0);
+			cqm_setup_limbo_handler(d, 0, RESCTRL_PICK_ANY_CPU);
 		}
 	}
 }
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 021a8956518c..9cba8fc405b9 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -79,6 +79,37 @@ static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask)
 	return cpu;
 }
 
+/**
+ * cpumask_any_housekeeping_but() - Chose any cpu in @mask, preferring those
+ *			            that aren't marked nohz_full, excluding
+ *				    the provided CPU
+ * @mask:	The mask to pick a CPU from.
+ * @exclude_cpu:The CPU to avoid picking.
+ *
+ * Returns a CPU from @mask, but not @but. If there are housekeeping CPUs that
+ * don't use nohz_full, these are preferred.
+ * Returns >= nr_cpu_ids if no CPUs are available.
+ */
+static inline unsigned int
+cpumask_any_housekeeping_but(const struct cpumask *mask, int exclude_cpu)
+{
+	int cpu, hk_cpu;
+
+	cpu = cpumask_any_but(mask, exclude_cpu);
+	if (tick_nohz_full_cpu(cpu)) {
+		hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
+		if  (hk_cpu == exclude_cpu) {
+			hk_cpu = cpumask_nth_andnot(1, mask,
+						    tick_nohz_full_mask);
+		}
+
+		if (hk_cpu < nr_cpu_ids)
+			cpu = hk_cpu;
+	}
+
+	return cpu;
+}
+
 struct rdt_fs_context {
 	struct kernfs_fs_context	kfc;
 	bool				enable_cdpl2;
@@ -564,11 +595,13 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
 		    struct rdt_domain *d, struct rdtgroup *rdtgrp,
 		    int evtid, int first);
 void mbm_setup_overflow_handler(struct rdt_domain *dom,
-				unsigned long delay_ms);
+				unsigned long delay_ms,
+				int exclude_cpu);
 void mbm_handle_overflow(struct work_struct *work);
 void __init intel_rdt_mbm_apply_quirk(void);
 bool is_mba_sc(struct rdt_resource *r);
-void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms);
+void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms,
+			     int exclude_cpu);
 void cqm_handle_limbo(struct work_struct *work);
 bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);
 void __check_limbo(struct rdt_domain *d, bool force_free);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ced933694f60..ae02185f3354 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -485,7 +485,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 		 * setup up the limbo worker.
 		 */
 		if (!has_busy_rmid(r, d))
-			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL);
+			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL, -1);
 		set_bit(idx, d->rmid_busy_llc);
 		entry->busy++;
 	}
@@ -810,15 +810,28 @@ void cqm_handle_limbo(struct work_struct *work)
 	mutex_unlock(&rdtgroup_mutex);
 }
 
-void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms)
+/**
+ * cqm_setup_limbo_handler() - Schedule the limbo handler to run for this
+ *                             domain.
+ * @delay_ms:      How far in the future the handler should run.
+ * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any CPU.
+ */
+void cqm_setup_limbo_handler(struct rdt_domain *dom, unsigned long delay_ms,
+			     int exclude_cpu)
 {
 	unsigned long delay = msecs_to_jiffies(delay_ms);
 	int cpu;
 
-	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
-	dom->cqm_work_cpu = cpu;
+	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
+		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
+	else
+		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
+						   exclude_cpu);
 
-	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
+	if (cpu < nr_cpu_ids) {
+		dom->cqm_work_cpu = cpu;
+		schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
+	}
 }
 
 void mbm_handle_overflow(struct work_struct *work)
@@ -864,7 +877,14 @@ void mbm_handle_overflow(struct work_struct *work)
 	mutex_unlock(&rdtgroup_mutex);
 }
 
-void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
+/**
+ * mbm_setup_overflow_handler() - Schedule the overflow handler to run for this
+ *                                domain.
+ * @delay_ms:      How far in the future the handler should run.
+ * @exclude_cpu:   Which CPU the handler should not run on, -1 to pick any CPU.
+ */
+void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms,
+				int exclude_cpu)
 {
 	unsigned long delay = msecs_to_jiffies(delay_ms);
 	int cpu;
@@ -875,9 +895,15 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 	 */
 	if (!resctrl_mounted || !resctrl_arch_mon_capable())
 		return;
-	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
+	if (exclude_cpu == -1)
+		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
+	else
+		cpu = cpumask_any_housekeeping_but(&dom->cpu_mask,
+						   exclude_cpu);
 	dom->mbm_work_cpu = cpu;
-	schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
+
+	if (cpu < nr_cpu_ids)
+		schedule_delayed_work_on(cpu, &dom->mbm_over, delay);
 }
 
 static int dom_data_init(struct rdt_resource *r)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 7c3de5ea0482..3373b11afe01 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2539,7 +2539,8 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (is_mbm_enabled()) {
 		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
 		list_for_each_entry(dom, &r->domains, list)
-			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL);
+			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL,
+						   RESCTRL_PICK_ANY_CPU);
 	}
 
 	goto out;
@@ -3709,7 +3710,8 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
 
 	if (is_mbm_enabled()) {
 		INIT_DELAYED_WORK(&d->mbm_over, mbm_handle_overflow);
-		mbm_setup_overflow_handler(d, MBM_OVERFLOW_INTERVAL);
+		mbm_setup_overflow_handler(d, MBM_OVERFLOW_INTERVAL,
+					   RESCTRL_PICK_ANY_CPU);
 	}
 
 	if (is_llc_occupancy_enabled())
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index ecd41762d61a..089b91133e5e 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -9,6 +9,9 @@
 /* CLOSID value used by the default control group */
 #define RESCTRL_RESERVED_CLOSID		0
 
+/* Indicates no CPU needs to be excluded */
+#define RESCTRL_PICK_ANY_CPU		-1
+
 #ifdef CONFIG_PROC_CPU_RESCTRL
 
 int proc_resctrl_show(struct seq_file *m,
-- 
2.39.2