[PATCH v7 09/12] virt/steal_monitor: Add control knobs for handling steal values

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

These are the knobs to control the steal_monitor.

interval_ms:
How often steal monitor checks for steal time.
(Default: 1000 i.e 1 second)
This controls how fast steal monitor driver reacts to changes to
the contention of physical CPUs. Since it does a fair amount of
work, setting too low will have overheads. Setting it too high
might render the feature ineffective.
Can be set between 10 to 100000. i.e. 10ms to 100seconds.

low_threshold:
lower threshold value in percentage * 100.
(Default: 200, i.e 2% steal is considered as low threshold)
This determines what values should be considered as nil/no steal values.
When steal monitor see steal time is below or equal to this value, it
will increase the preferred CPUs by 1 core. Having value as zero
might cause oscillations

high_threshold:
higher threshold value in percentage * 100
(Default: 500, i.e 5% steal is considered as high threshold)
This determines what values should be considered as high steal values.
When steal monitor sees steal time is higher than this value, it will
reduce the preferred CPUs by 1 core.

module_param_cb methods are used to do the validation checks.
This helps to ensure one configures sane values.
Parameters values can't be changed at runtime. One has to unload
the module and change it.

Also available at: Documentation/driver-api/steal-monitor.rst

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
v6->v7:
- Add module_param_cb to do parameter checks.
- Make parameters read only after module load.


 drivers/virt/steal_monitor/sm_core.c | 92 +++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 1 deletion(-)

diff --git a/drivers/virt/steal_monitor/sm_core.c b/drivers/virt/steal_monitor/sm_core.c
index 180db424846c..4a03c14337be 100644
--- a/drivers/virt/steal_monitor/sm_core.c
+++ b/drivers/virt/steal_monitor/sm_core.c
@@ -14,7 +14,97 @@
 
 #include "sm_core.h"
 
-struct steal_monitor sm_core_ctx;
+struct steal_monitor sm_core_ctx = {
+	.interval_ms = 1000,	/* 1 second */
+	.high_threshold = 500,	/* 5% */
+	.low_threshold = 200,	/* 2% */
+};
+
+static int param_set_interval_ms(const char *val, const struct kernel_param *kp)
+{
+	unsigned int interval;
+	int ret;
+
+	ret = kstrtouint(val, 0, &interval);
+	if (ret)
+		return ret;
+
+	if (interval < 10 || interval > 100000) {
+		pr_err("steal_monitor: interval_ms must be between 10 and 100000\n");
+		return -EINVAL;
+	}
+
+	return param_set_uint(val, kp);
+}
+
+static const struct kernel_param_ops interval_ms_ops = {
+	.set = param_set_interval_ms,
+	.get = param_get_uint,
+};
+
+module_param_cb(interval_ms, &interval_ms_ops, &sm_core_ctx.interval_ms, 0444);
+MODULE_PARM_DESC(interval_ms,
+		 "Sampling frequency in milliseconds. default: 1000");
+
+static int param_set_high_threshold(const char *val, const struct kernel_param *kp)
+{
+	unsigned int threshold;
+	int ret;
+
+	ret = kstrtouint(val, 0, &threshold);
+	if (ret)
+		return ret;
+
+	if (threshold <= sm_core_ctx.low_threshold) {
+		pr_err("steal_monitor: high_threshold (%u) must be more than low_threshold (%u)\n",
+		       threshold, sm_core_ctx.low_threshold);
+		return -EINVAL;
+	}
+
+	if (threshold >= 100 * 100) {
+		pr_err("steal_monitor: high_threshold (%u) can't be more than 99.99%%\n",
+		       threshold);
+		return -EINVAL;
+	}
+
+	return param_set_uint(val, kp);
+}
+
+static const struct kernel_param_ops high_threshold_ops = {
+	.set = param_set_high_threshold,
+	.get = param_get_uint,
+};
+
+module_param_cb(high_threshold, &high_threshold_ops, &sm_core_ctx.high_threshold, 0444);
+MODULE_PARM_DESC(high_threshold,
+		 "High steal threshold. default: 500 i.e 5%. Must be > low_threshold");
+
+static int param_set_low_threshold(const char *val, const struct kernel_param *kp)
+{
+	unsigned int threshold;
+	int ret;
+
+	ret = kstrtouint(val, 0, &threshold);
+	if (ret)
+		return ret;
+
+	if (threshold >= sm_core_ctx.high_threshold) {
+		pr_err("steal_monitor: low_threshold (%u) must be less than high_threshold (%u)\n",
+		       threshold, sm_core_ctx.high_threshold);
+		return -EINVAL;
+	}
+
+	return param_set_uint(val, kp);
+}
+
+static const struct kernel_param_ops low_threshold_ops = {
+	.set = param_set_low_threshold,
+	.get = param_get_uint,
+};
+
+module_param_cb(low_threshold, &low_threshold_ops, &sm_core_ctx.low_threshold, 0444);
+MODULE_PARM_DESC(low_threshold,
+		 "Low steal threshold. default: 200 i.e 2%. Must be < high_threshold");
 
 static int __init steal_monitor_init(void)
 {
-- 
2.47.3