[PATCH 3/3] x86/intel_rdt/cqm: Improve limbo list processing

[Vikas Shivappa]

During a mkdir, we synchronously check the entire limbo list on each
package for free RMIDs by sending IPIs and the worst case would end up
taking more than tolerable amount of time in IPIs. For ex: On SKL we
could end up reading all 192 RMIDs for llc_occupancy.

Modify this to make some improvements mainly avoiding the use of IPIs.
We use asynchronous worker threads on each package which would
periodically scan the limbo list and move the RMIDs that have:

	llc_occupancy < threshold_occupancy

on all packages to free list. The mkdir would simply return -ENOSPC if the
limbo list is empty or would return -EBUSY if there are RMIDs on limbo
but not on free list.  As a side effect of not accessing the limbo list
in parallel on IPIs we simplify some of the related data structures.

Signed-off-by: Vikas Shivappa <vikas.shivappa@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/intel_rdt.c         |  25 +++-
 arch/x86/kernel/cpu/intel_rdt.h         |  10 ++
 arch/x86/kernel/cpu/intel_rdt_monitor.c | 209 ++++++++++++++------------------
 3 files changed, 120 insertions(+), 124 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index 97c8d83..792f142 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -426,6 +426,9 @@ static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 					   GFP_KERNEL);
 		if (!d->rmid_busy_llc)
 			return -ENOMEM;
+		INIT_DELAYED_WORK(&d->cqm_limbo, cqm_handle_limbo);
+		if (has_busy_rmid(r, d))
+			cqm_setup_limbo_handler(d);
 	}
 	if (is_mbm_total_enabled()) {
 		tsize = sizeof(*d->mbm_total);
@@ -536,11 +539,25 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 		list_del(&d->list);
 		if (is_mbm_enabled())
 			cancel_delayed_work(&d->mbm_over);
+
+		if (is_llc_occupancy_enabled() &&
+		    has_busy_rmid(r, d))
+			cancel_delayed_work(&d->cqm_limbo);
+
 		kfree(d);
-	} else if (r == &rdt_resources_all[RDT_RESOURCE_L3] &&
-		   cpu == d->mbm_work_cpu && is_mbm_enabled()) {
-		cancel_delayed_work(&d->mbm_over);
-		mbm_setup_overflow_handler(d);
+		return;
+	}
+
+	if (r == &rdt_resources_all[RDT_RESOURCE_L3]) {
+		if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
+			cancel_delayed_work(&d->mbm_over);
+			mbm_setup_overflow_handler(d);
+		}
+		if (is_llc_occupancy_enabled() && cpu == d->mbm_work_cpu &&
+		    has_busy_rmid(r, d)) {
+			cancel_delayed_work(&d->cqm_limbo);
+			cqm_setup_limbo_handler(d);
+		}
 	}
 }
 
diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
index 4040bf1..6d57d7e 100644
--- a/arch/x86/kernel/cpu/intel_rdt.h
+++ b/arch/x86/kernel/cpu/intel_rdt.h
@@ -20,6 +20,8 @@
 #define QOS_L3_MBM_TOTAL_EVENT_ID	0x02
 #define QOS_L3_MBM_LOCAL_EVENT_ID	0x03
 
+#define CQM_LIMBOCHECK_INTERVAL	1000
+
 #define MBM_CNTR_WIDTH			24
 #define MBM_OVERFLOW_INTERVAL		1000
 
@@ -187,8 +189,11 @@ struct mbm_state {
  * @mbm_total:	saved state for MBM total bandwidth
  * @mbm_local:	saved state for MBM local bandwidth
  * @mbm_over:	worker to periodically read MBM h/w counters
+ * @cqm_limbo:	worker to periodically read CQM h/w counters
  * @mbm_work_cpu:
  *		worker cpu for MBM h/w counters
+ * @cqm_work_cpu:
+ *		worker cpu for CQM h/w counters
  * @ctrl_val:	array of cache or mem ctrl values (indexed by CLOSID)
  * @new_ctrl:	new ctrl value to be loaded
  * @have_new_ctrl: did user provide new_ctrl for this domain
@@ -201,7 +206,9 @@ struct rdt_domain {
 	struct mbm_state	*mbm_total;
 	struct mbm_state	*mbm_local;
 	struct delayed_work	mbm_over;
+	struct delayed_work	cqm_limbo;
 	int			mbm_work_cpu;
+	int			cqm_work_cpu;
 	u32			*ctrl_val;
 	u32			new_ctrl;
 	bool			have_new_ctrl;
@@ -424,5 +431,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_domain *d,
 		    struct rdtgroup *rdtgrp, int evtid, int first);
 void mbm_setup_overflow_handler(struct rdt_domain *dom);
 void mbm_handle_overflow(struct work_struct *work);
+void cqm_setup_limbo_handler(struct rdt_domain *dom);
+void cqm_handle_limbo(struct work_struct *work);
+bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);
 
 #endif /* _ASM_X86_INTEL_RDT_H */
diff --git a/arch/x86/kernel/cpu/intel_rdt_monitor.c b/arch/x86/kernel/cpu/intel_rdt_monitor.c
index d6bfdfd..d9c03a0 100644
--- a/arch/x86/kernel/cpu/intel_rdt_monitor.c
+++ b/arch/x86/kernel/cpu/intel_rdt_monitor.c
@@ -33,7 +33,7 @@
 
 struct rmid_entry {
 	u32				rmid;
-	atomic_t			busy;
+	int				busy;
 	struct list_head		list;
 };
 
@@ -45,13 +45,13 @@ struct rmid_entry {
 static LIST_HEAD(rmid_free_lru);
 
 /**
- * @rmid_limbo_lru       list of currently unused but (potentially)
+ * @rmid_limbo_count     count of currently unused but (potentially)
  *     dirty RMIDs.
- *     This list contains RMIDs that no one is currently using but that
+ *     This counts RMIDs that no one is currently using but that
  *     may have a occupancy value > intel_cqm_threshold. User can change
  *     the threshold occupancy value.
  */
-static LIST_HEAD(rmid_limbo_lru);
+unsigned int rmid_limbo_count;
 
 /**
  * @rmid_entry - The entry in the limbo and free lists.
@@ -104,123 +104,45 @@ static u64 __rmid_read(u32 rmid, u32 eventid)
 }
 
 /*
- * Walk the limbo list looking at any RMIDs that are flagged in the
- * domain rmid_busy_llc bitmap as busy. If the reported LLC occupancy
- * is below the threshold clear the busy bit and decrement the count.
- * If the busy count gets to zero on an RMID we stop looking.
- * This can be called from an IPI.
- * We need an atomic for the busy count because multiple CPUs may check
- * the same RMID at the same time.
+ * Check the RMIDs that are marked as busy for this domain. If the
+ * reported LLC occupancy is below the threshold clear the busy bit and
+ * decrement the count. If the busy count gets to zero on an RMID, we
+ * free the RMID
  */
-static bool __check_limbo(struct rdt_domain *d)
+static void __check_limbo(struct rdt_domain *d)
 {
 	struct rmid_entry *entry;
-	u64 val;
-
-	list_for_each_entry(entry, &rmid_limbo_lru, list) {
-		if (!test_bit(entry->rmid, d->rmid_busy_llc))
-			continue;
-		val = __rmid_read(entry->rmid, QOS_L3_OCCUP_EVENT_ID);
-		if (val <= intel_cqm_threshold) {
-			clear_bit(entry->rmid, d->rmid_busy_llc);
-			if (atomic_dec_and_test(&entry->busy))
-				return true;
-		}
-	}
-	return false;
-}
-
-static void check_limbo(void *arg)
-{
-	struct rdt_domain *d;
-
-	d = get_domain_from_cpu(smp_processor_id(),
-				&rdt_resources_all[RDT_RESOURCE_L3]);
-
-	if (d)
-		__check_limbo(d);
-}
-
-static bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
-{
-	return find_first_bit(d->rmid_busy_llc, r->num_rmid) != r->num_rmid;
-}
-
-/*
- * Scan the limbo list and move all entries that are below the
- * intel_cqm_threshold to the free list.
- * Return "true" if the limbo list is empty, "false" if there are
- * still some RMIDs there.
- */
-static bool try_freeing_limbo_rmid(void)
-{
-	struct rmid_entry *entry, *tmp;
 	struct rdt_resource *r;
-	cpumask_var_t cpu_mask;
-	struct rdt_domain *d;
-	bool ret = true;
-	int cpu;
-
-	if (list_empty(&rmid_limbo_lru))
-		return ret;
+	u32 crmid = 1, nrmid;
+	u64 val;
 
 	r = &rdt_resources_all[RDT_RESOURCE_L3];
 
-	cpu = get_cpu();
-
 	/*
-	 * First see if we can free up an RMID by checking busy values
-	 * on the local package.
+	 * We skip the RMID 0 and start from RMID 1 and check all
+	 * the RMIDs that are marked as busy if the occupancy < threshold.
 	 */
-	d = get_domain_from_cpu(cpu, r);
-	if (d && has_busy_rmid(r, d) && __check_limbo(d)) {
-		list_for_each_entry_safe(entry, tmp, &rmid_limbo_lru, list) {
-			if (atomic_read(&entry->busy) == 0) {
-				list_del(&entry->list);
+	for (;;) {
+		nrmid = find_next_bit(d->rmid_busy_llc, r->num_rmid, crmid);
+		if (nrmid == r->num_rmid)
+			break;
+
+		entry = __rmid_entry(nrmid);
+		val = __rmid_read(entry->rmid, QOS_L3_OCCUP_EVENT_ID);
+		if (val <= intel_cqm_threshold) {
+			clear_bit(entry->rmid, d->rmid_busy_llc);
+			if (!--entry->busy) {
+				rmid_limbo_count--;
 				list_add_tail(&entry->list, &rmid_free_lru);
-				goto done;
 			}
 		}
+		crmid = nrmid + 1;
 	}
+}
 
-	if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL)) {
-		ret = false;
-		goto done;
-	}
-
-	/*
-	 * Build a mask of other domains that have busy RMIDs
-	 */
-	list_for_each_entry(d, &r->domains, list) {
-		if (!cpumask_test_cpu(cpu, &d->cpu_mask) &&
-		    has_busy_rmid(r, d))
-			cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);
-	}
-	if (cpumask_empty(cpu_mask)) {
-		ret = false;
-		goto free_mask;
-	}
-
-	/*
-	 * Scan domains with busy RMIDs to check if they still are busy
-	 */
-	on_each_cpu_mask(cpu_mask, check_limbo, NULL, true);
-
-	/* Walk limbo list moving all free RMIDs to the &rmid_free_lru list */
-	list_for_each_entry_safe(entry, tmp, &rmid_limbo_lru, list) {
-		if (atomic_read(&entry->busy) != 0) {
-			ret = false;
-			continue;
-		}
-		list_del(&entry->list);
-		list_add_tail(&entry->list, &rmid_free_lru);
-	}
-
-free_mask:
-	free_cpumask_var(cpu_mask);
-done:
-	put_cpu();
-	return ret;
+bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
+{
+	return find_first_bit(d->rmid_busy_llc, r->num_rmid) != r->num_rmid;
 }
 
 /*
@@ -231,15 +153,11 @@ static bool try_freeing_limbo_rmid(void)
 int alloc_rmid(void)
 {
 	struct rmid_entry *entry;
-	bool ret;
 
 	lockdep_assert_held(&rdtgroup_mutex);
 
-	if (list_empty(&rmid_free_lru)) {
-		ret = try_freeing_limbo_rmid();
-		if (list_empty(&rmid_free_lru))
-			return ret ? -ENOSPC : -EBUSY;
-	}
+	if (list_empty(&rmid_free_lru))
+		return rmid_limbo_count ? -EBUSY : -ENOSPC;
 
 	entry = list_first_entry(&rmid_free_lru,
 				 struct rmid_entry, list);
@@ -252,11 +170,12 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 {
 	struct rdt_resource *r;
 	struct rdt_domain *d;
-	int cpu, nbusy = 0;
+	int cpu;
 	u64 val;
 
 	r = &rdt_resources_all[RDT_RESOURCE_L3];
 
+	entry->busy = 0;
 	cpu = get_cpu();
 	list_for_each_entry(d, &r->domains, list) {
 		if (cpumask_test_cpu(cpu, &d->cpu_mask)) {
@@ -264,17 +183,22 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 			if (val <= intel_cqm_threshold)
 				continue;
 		}
+
+		/*
+		 * For the first limbo RMID in the domain,
+		 * setup up the limbo worker.
+		 */
+		if (!has_busy_rmid(r, d))
+			cqm_setup_limbo_handler(d);
 		set_bit(entry->rmid, d->rmid_busy_llc);
-		nbusy++;
+		entry->busy++;
 	}
 	put_cpu();
 
-	if (nbusy) {
-		atomic_set(&entry->busy, nbusy);
-		list_add_tail(&entry->list, &rmid_limbo_lru);
-	} else {
+	if (entry->busy)
+		rmid_limbo_count++;
+	else
 		list_add_tail(&entry->list, &rmid_free_lru);
-	}
 }
 
 void free_rmid(u32 rmid)
@@ -387,6 +311,51 @@ static void mbm_update(struct rdt_domain *d, int rmid)
 	}
 }
 
+/*
+ * Handler to scan the limbo list and move the RMIDs
+ * to free list whose occupancy < threshold_occupancy.
+ */
+void cqm_handle_limbo(struct work_struct *work)
+{
+	unsigned long delay = msecs_to_jiffies(CQM_LIMBOCHECK_INTERVAL);
+	int cpu = smp_processor_id();
+	struct rdt_resource *r;
+	struct rdt_domain *d;
+
+	mutex_lock(&rdtgroup_mutex);
+
+	r = &rdt_resources_all[RDT_RESOURCE_L3];
+	d = get_domain_from_cpu(cpu, r);
+
+	if (!d) {
+		pr_warn_once("Failure to get domain for limbo worker\n");
+		goto out_unlock;
+	}
+
+	__check_limbo(d);
+
+	if (!has_busy_rmid(r, d))
+		goto out_unlock;
+	schedule_delayed_work_on(cpu, &d->cqm_limbo, delay);
+
+out_unlock:
+	mutex_unlock(&rdtgroup_mutex);
+}
+
+void cqm_setup_limbo_handler(struct rdt_domain *dom)
+{
+	unsigned long delay = msecs_to_jiffies(CQM_LIMBOCHECK_INTERVAL);
+	struct rdt_resource *r;
+	int cpu;
+
+	r = &rdt_resources_all[RDT_RESOURCE_L3];
+
+	cpu = cpumask_any(&dom->cpu_mask);
+	dom->cqm_work_cpu = cpu;
+
+	schedule_delayed_work_on(cpu, &dom->cqm_limbo, delay);
+}
+
 void mbm_handle_overflow(struct work_struct *work)
 {
 	unsigned long delay = msecs_to_jiffies(MBM_OVERFLOW_INTERVAL);
-- 
1.9.1