Subject: [PATCH] cpuidle: Add a sysfs entry to disable specific C state for debug purpose.

Liu, ShuoX
2012-02-29T04:56:58Z

From: ShuoX Liu <shuox.liu@intel.com>

Some C states of new CPU might be not good. One reason is BIOS might configure
them incorrectly. To help developers root cause it quickly, the patch adds a
new sysfs entry, so developers could disable specific C state manually.

In addition, C state might have much impact on performance tuning, as it takes
much time to enter/exit C states, which might delay interrupt processing. With
the new debug option, developers could check if a deep C state could impact
performance and how much impact it could cause.

Signed-off-by: ShuoX Liu <shuox.liu@intel.com>
---
drivers/cpuidle/cpuidle.c | 1 +
drivers/cpuidle/governors/menu.c | 5 ++++-
drivers/cpuidle/sysfs.c | 34 ++++++++++++++++++++++++++++++++++
include/linux/cpuidle.h | 1 +
4 files changed, 40 insertions(+), 1 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 59f4261..7d66d3e 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -197,6 +197,7 @@ static void poll_idle_init(struct cpuidle_driver *drv)
state->power_usage = -1;
state->flags = 0;
state->enter = poll_idle;
+ state->disable = 0;
}
#else
static void poll_idle_init(struct cpuidle_driver *drv) {}
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index ad09526..5c17ca1 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -280,7 +280,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
* We want to default to C1 (hlt), not to busy polling
* unless the timer is happening really really soon.
*/
- if (data->expected_us > 5)
+ if (data->expected_us > 5 &&
+ drv->states[CPUIDLE_DRIVER_STATE_START].disable == 0)
data->last_state_idx = CPUIDLE_DRIVER_STATE_START;

/*
@@ -290,6 +291,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
struct cpuidle_state *s = &drv->states[i];

+ if (s->disable)
+ continue;
if (s->target_residency > data->predicted_us)
continue;
if (s->exit_latency > latency_req)
diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
index 3fe41fe..1eae29a 100644
--- a/drivers/cpuidle/sysfs.c
+++ b/drivers/cpuidle/sysfs.c
@@ -222,6 +222,9 @@ struct cpuidle_state_attr {
#define define_one_state_ro(_name, show) \
static struct cpuidle_state_attr attr_##_name = __ATTR(_name, 0444, show, NULL)

+#define define_one_state_rw(_name, show, store) \
+static struct cpuidle_state_attr attr_##_name = __ATTR(_name, 0644, show, store)
+
#define define_show_state_function(_name) \
static ssize_t show_state_##_name(struct cpuidle_state *state, \
struct cpuidle_state_usage *state_usage, char *buf) \
@@ -229,6 +232,19 @@ static ssize_t show_state_##_name(struct cpuidle_state *state, \
return sprintf(buf, "%u\n", state->_name);\
}

+#define define_store_state_function(_name) \
+static ssize_t store_state_##_name(struct cpuidle_state *state, \
+ const char *buf, size_t size) \
+{ \
+ int value; \
+ sscanf(buf, "%d", &value); \
+ if (value) \
+ state->disable = 1; \
+ else \
+ state->disable = 0; \
+ return size; \
+}
+
#define define_show_state_ull_function(_name) \
static ssize_t show_state_##_name(struct cpuidle_state *state, \
struct cpuidle_state_usage *state_usage, char *buf) \
@@ -251,6 +267,8 @@ define_show_state_ull_function(usage)
define_show_state_ull_function(time)
define_show_state_str_function(name)
define_show_state_str_function(desc)
+define_show_state_function(disable)
+define_store_state_function(disable)

define_one_state_ro(name, show_state_name);
define_one_state_ro(desc, show_state_desc);
@@ -258,6 +276,7 @@ define_one_state_ro(latency, show_state_exit_latency);
define_one_state_ro(power, show_state_power_usage);
define_one_state_ro(usage, show_state_usage);
define_one_state_ro(time, show_state_time);
+define_one_state_rw(disable, show_state_disable, store_state_disable);

static struct attribute *cpuidle_state_default_attrs[] = {
&attr_name.attr,
@@ -266,6 +285,7 @@ static struct attribute *cpuidle_state_default_attrs[] = {
&attr_power.attr,
&attr_usage.attr,
&attr_time.attr,
+ &attr_disable.attr,
NULL
};

@@ -287,8 +307,22 @@ static ssize_t cpuidle_state_show(struct kobject * kobj,
return ret;
}

+static ssize_t cpuidle_state_store(struct kobject *kobj,
+ struct attribute *attr, const char *buf, size_t size)
+{
+ int ret = -EIO;
+ struct cpuidle_state *state = kobj_to_state(kobj);
+ struct cpuidle_state_attr *cattr = attr_to_stateattr(attr);
+
+ if (cattr->store)
+ ret = cattr->store(state, buf, size);
+
+ return ret;
+}
+
static const struct sysfs_ops cpuidle_state_sysfs_ops = {
.show = cpuidle_state_show,
+ .store = cpuidle_state_store,
};

static void cpuidle_state_sysfs_release(struct kobject *kobj)
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 712abcc..eb150a5 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -45,6 +45,7 @@ struct cpuidle_state {
unsigned int exit_latency; /* in US */
unsigned int power_usage; /* in mW */
unsigned int target_residency; /* in US */
+ unsigned int disable;

int (*enter) (struct cpuidle_device *dev,
struct cpuidle_driver *drv,
--
1.7.1