x86/intel_rdt: Limit C-states dynamically when pseudo-locking active

Deeper C-states impact cache content through shrinking of the cache or
flushing entire cache to memory before reducing power to the cache.
Deeper C-states will thus negatively impact the pseudo-locked regions.

To avoid impacting pseudo-locked regions C-states are limited on
pseudo-locked region creation so that cores associated with the
pseudo-locked region are prevented from entering deeper C-states.
This is accomplished by requesting a CPU latency target which will
prevent the core from entering C6 across all supported platforms.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: vikas.shivappa@linux.intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/1ef4f99dd6ba12fa6fb44c5a1141e75f952b9cd9.1529706536.git.reinette.chatre@intel.com

2 files changed, 85 insertions, 2 deletions

diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
index b8e490a43290..2d9cbb9d7a58 100644
--- a/arch/x86/kernel/cpu/intel_rdt.h
+++ b/arch/x86/kernel/cpu/intel_rdt.h
@@ -142,6 +142,7 @@ struct mongroup {
  *			region
  * @debugfs_dir:	pointer to this region's directory in the debugfs
  *			filesystem
+ * @pm_reqs:		Power management QoS requests related to this region
  */
 struct pseudo_lock_region {
 	struct rdt_resource	*r;
@@ -155,6 +156,7 @@ struct pseudo_lock_region {
 	void			*kmem;
 	unsigned int		minor;
 	struct dentry		*debugfs_dir;
+	struct list_head	pm_reqs;
 };
 
 /**
diff --git a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
index dd1341557c9d..6e83f61552a5 100644
--- a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
+++ b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
@@ -17,6 +17,7 @@
 #include <linux/debugfs.h>
 #include <linux/kthread.h>
 #include <linux/mman.h>
+#include <linux/pm_qos.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 
@@ -176,6 +177,76 @@ static struct rdtgroup *region_find_by_minor(unsigned int minor)
 }
 
 /**
+ * pseudo_lock_pm_req - A power management QoS request list entry
+ * @list:	Entry within the @pm_reqs list for a pseudo-locked region
+ * @req:	PM QoS request
+ */
+struct pseudo_lock_pm_req {
+	struct list_head list;
+	struct dev_pm_qos_request req;
+};
+
+static void pseudo_lock_cstates_relax(struct pseudo_lock_region *plr)
+{
+	struct pseudo_lock_pm_req *pm_req, *next;
+
+	list_for_each_entry_safe(pm_req, next, &plr->pm_reqs, list) {
+		dev_pm_qos_remove_request(&pm_req->req);
+		list_del(&pm_req->list);
+		kfree(pm_req);
+	}
+}
+
+/**
+ * pseudo_lock_cstates_constrain - Restrict cores from entering C6
+ *
+ * To prevent the cache from being affected by power management entering
+ * C6 has to be avoided. This is accomplished by requesting a latency
+ * requirement lower than lowest C6 exit latency of all supported
+ * platforms as found in the cpuidle state tables in the intel_idle driver.
+ * At this time it is possible to do so with a single latency requirement
+ * for all supported platforms.
+ *
+ * Since Goldmont is supported, which is affected by X86_BUG_MONITOR,
+ * the ACPI latencies need to be considered while keeping in mind that C2
+ * may be set to map to deeper sleep states. In this case the latency
+ * requirement needs to prevent entering C2 also.
+ */
+static int pseudo_lock_cstates_constrain(struct pseudo_lock_region *plr)
+{
+	struct pseudo_lock_pm_req *pm_req;
+	int cpu;
+	int ret;
+
+	for_each_cpu(cpu, &plr->d->cpu_mask) {
+		pm_req = kzalloc(sizeof(*pm_req), GFP_KERNEL);
+		if (!pm_req) {
+			rdt_last_cmd_puts("fail allocating mem for PM QoS\n");
+			ret = -ENOMEM;
+			goto out_err;
+		}
+		ret = dev_pm_qos_add_request(get_cpu_device(cpu),
+					     &pm_req->req,
+					     DEV_PM_QOS_RESUME_LATENCY,
+					     30);
+		if (ret < 0) {
+			rdt_last_cmd_printf("fail to add latency req cpu%d\n",
+					    cpu);
+			kfree(pm_req);
+			ret = -1;
+			goto out_err;
+		}
+		list_add(&pm_req->list, &plr->pm_reqs);
+	}
+
+	return 0;
+
+out_err:
+	pseudo_lock_cstates_relax(plr);
+	return ret;
+}
+
+/**
  * pseudo_lock_region_init - Initialize pseudo-lock region information
  * @plr: pseudo-lock region
  *
@@ -242,6 +313,7 @@ static int pseudo_lock_init(struct rdtgroup *rdtgrp)
 		return -ENOMEM;
 
 	init_waitqueue_head(&plr->lock_thread_wq);
+	INIT_LIST_HEAD(&plr->pm_reqs);
 	rdtgrp->plr = plr;
 	return 0;
 }
@@ -1135,6 +1207,12 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
 	if (ret < 0)
 		return ret;
 
+	ret = pseudo_lock_cstates_constrain(plr);
+	if (ret < 0) {
+		ret = -EINVAL;
+		goto out_region;
+	}
+
 	plr->thread_done = 0;
 
 	thread = kthread_create_on_node(pseudo_lock_fn, rdtgrp,
@@ -1143,7 +1221,7 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
 	if (IS_ERR(thread)) {
 		ret = PTR_ERR(thread);
 		rdt_last_cmd_printf("locking thread returned error %d\n", ret);
-		goto out_region;
+		goto out_cstates;
 	}
 
 	kthread_bind(thread, plr->cpu);
@@ -1161,7 +1239,7 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
 		 * empty pseudo-locking loop.
 		 */
 		rdt_last_cmd_puts("locking thread interrupted\n");
-		goto out_region;
+		goto out_cstates;
 	}
 
 	if (!IS_ERR_OR_NULL(debugfs_resctrl)) {
@@ -1222,6 +1300,8 @@ out_minor:
 	pseudo_lock_minor_release(new_minor);
 out_debugfs:
 	debugfs_remove_recursive(plr->debugfs_dir);
+out_cstates:
+	pseudo_lock_cstates_relax(plr);
 out_region:
 	pseudo_lock_region_clear(plr);
 out:
@@ -1255,6 +1335,7 @@ void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp)
 		goto free;
 	}
 
+	pseudo_lock_cstates_relax(plr);
 	debugfs_remove_recursive(rdtgrp->plr->debugfs_dir);
 	device_destroy(pseudo_lock_class, MKDEV(pseudo_lock_major, plr->minor));
 	pseudo_lock_minor_release(plr->minor);