[PATCH v6 16/23] virt/steal_monitor: Compute work at regular intervals

[Shrikanth Hegde <sshegde@linux.ibm.com>]

This is the steal_monitor core functionality done in periodic work

- Calculate the steal_ratio. It is multiplied by 100 to consider the
  fractional values of steal time. I.e 10 means 0.1% steal time.
- If steal value is higher than high threshold, call the method to reduce
  the preferred CPUs.
- If steal value is lower or equal to low threshold, call the method to
  increase the preferred CPUs.
- If the steal value is in between, no action is taken.
- Save the values for next delta calculations.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 drivers/virt/steal_monitor/sm_core.c | 26 +++++++++++++++++++++++++-
 drivers/virt/steal_monitor/sm_core.h |  3 +++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/virt/steal_monitor/sm_core.c b/drivers/virt/steal_monitor/sm_core.c
index 1ba638224abb..b499faa61010 100644
--- a/drivers/virt/steal_monitor/sm_core.c
+++ b/drivers/virt/steal_monitor/sm_core.c
@@ -32,9 +32,32 @@ module_param_named(low_threshold, sm_core_ctx.low_threshold, uint, 0644);
 MODULE_PARM_DESC(low_threshold,
 		 "Low steal threshold (default: 200 i.e 2%)");
 
+static void compute_preferred_cpus_work(struct work_struct *work)
+{
+	/* At least one core is kept as preferred */
+	WARN_ON(cpumask_empty(cpu_preferred_mask));
+
+	/* Warn if interval_ms is set to 0, that might cause lockup. */
+	if (unlikely(sm_core_ctx.interval_ms == 0)) {
+		WARN_ON(1);
+		sm_core_ctx.interval_ms = 1000; /* Fallback to default */
+	}
+
+	/* Trigger for next sampling */
+	schedule_delayed_work(&sm_core_ctx.work,
+			      msecs_to_jiffies(sm_core_ctx.interval_ms));
+}
+
 static int __init steal_monitor_init(void)
 {
-	pr_info("steal_monitor is enabled\n");
+	pr_info("steal_monitor is enabled. interval: %ums, high_threshold: %u, low_threshold: %u\n",
+		sm_core_ctx.interval_ms, sm_core_ctx.high_threshold, sm_core_ctx.low_threshold);
+
+	INIT_DELAYED_WORK(&sm_core_ctx.work, compute_preferred_cpus_work);
+
+	schedule_delayed_work(&sm_core_ctx.work,
+			      msecs_to_jiffies(sm_core_ctx.interval_ms));
+
 	return 0;
 }
 
@@ -42,6 +65,7 @@ static void __exit steal_monitor_exit(void)
 {
 	pr_info("steal_monitor is disabled\n");
 
+	cancel_delayed_work_sync(&sm_core_ctx.work);
 	guard(cpus_read_lock)();
 	cpumask_copy(&__cpu_preferred_mask, cpu_active_mask);
 }
diff --git a/drivers/virt/steal_monitor/sm_core.h b/drivers/virt/steal_monitor/sm_core.h
index e5c3ea0a63c9..ea06e83c228c 100644
--- a/drivers/virt/steal_monitor/sm_core.h
+++ b/drivers/virt/steal_monitor/sm_core.h
@@ -8,6 +8,9 @@
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/cpuhplock.h>
+#include <linux/cpumask.h>
+#include <linux/workqueue.h>
+#include <linux/sched/isolation.h>
 
 struct steal_monitor {
 	struct delayed_work	work;
-- 
2.47.3