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    Subject[linux-pm] [PATCH v4] cpuidle: Add a sysfs entry to disable specific C state for debug purpose.
    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.

    Also add this option in Documentation/cpuidle/sysfs.txt.

    Signed-off-by: ShuoX Liu <shuox.liu@intel.com>
    Reviewed-by: Yanmin Zhang <yanmin_zhang@intel.com>
    Reviewed-and-Tested-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
    ---
    Thanks for all comments in previous mails. Here is the new patch.

    ---
    Documentation/cpuidle/sysfs.txt | 5 +++++
    drivers/cpuidle/cpuidle.c | 1 +
    drivers/cpuidle/governors/menu.c | 5 ++++-
    drivers/cpuidle/sysfs.c | 37 +++++++++++++++++++++++++++++++++++++
    include/linux/cpuidle.h | 1 +
    5 files changed, 48 insertions(+), 1 deletions(-)

    diff --git a/Documentation/cpuidle/sysfs.txt b/Documentation/cpuidle/sysfs.txt
    index 50d7b16..9d28a34 100644
    --- a/Documentation/cpuidle/sysfs.txt
    +++ b/Documentation/cpuidle/sysfs.txt
    @@ -36,6 +36,7 @@ drwxr-xr-x 2 root root 0 Feb 8 10:42 state3
    /sys/devices/system/cpu/cpu0/cpuidle/state0:
    total 0
    -r--r--r-- 1 root root 4096 Feb 8 10:42 desc
    +-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
    -r--r--r-- 1 root root 4096 Feb 8 10:42 latency
    -r--r--r-- 1 root root 4096 Feb 8 10:42 name
    -r--r--r-- 1 root root 4096 Feb 8 10:42 power
    @@ -45,6 +46,7 @@ total 0
    /sys/devices/system/cpu/cpu0/cpuidle/state1:
    total 0
    -r--r--r-- 1 root root 4096 Feb 8 10:42 desc
    +-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
    -r--r--r-- 1 root root 4096 Feb 8 10:42 latency
    -r--r--r-- 1 root root 4096 Feb 8 10:42 name
    -r--r--r-- 1 root root 4096 Feb 8 10:42 power
    @@ -54,6 +56,7 @@ total 0
    /sys/devices/system/cpu/cpu0/cpuidle/state2:
    total 0
    -r--r--r-- 1 root root 4096 Feb 8 10:42 desc
    +-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
    -r--r--r-- 1 root root 4096 Feb 8 10:42 latency
    -r--r--r-- 1 root root 4096 Feb 8 10:42 name
    -r--r--r-- 1 root root 4096 Feb 8 10:42 power
    @@ -63,6 +66,7 @@ total 0
    /sys/devices/system/cpu/cpu0/cpuidle/state3:
    total 0
    -r--r--r-- 1 root root 4096 Feb 8 10:42 desc
    +-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
    -r--r--r-- 1 root root 4096 Feb 8 10:42 latency
    -r--r--r-- 1 root root 4096 Feb 8 10:42 name
    -r--r--r-- 1 root root 4096 Feb 8 10:42 power
    @@ -72,6 +76,7 @@ total 0


    * desc : Small description about the idle state (string)
    +* disable : Option to disable this idle state (bool)
    * latency : Latency to exit out of this idle state (in microseconds)
    * name : Name of the idle state (string)
    * power : Power consumed while in this idle state (in milliwatts)
    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..f0fe0f5 100644
    --- a/drivers/cpuidle/sysfs.c
    +++ b/drivers/cpuidle/sysfs.c
    @@ -11,6 +11,7 @@
    #include <linux/sysfs.h>
    #include <linux/slab.h>
    #include <linux/cpu.h>
    +#include <linux/capability.h>

    #include "cpuidle.h"

    @@ -222,6 +223,9 @@ 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 +233,21 @@ 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) \
    +{ \
    + long value; \
    + if (!capable(CAP_SYS_ADMIN)) \
    + return -EPERM; \
    + kstrtol(buf, 0, &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 +270,8 @@ 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 +279,7 @@ 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 +288,7 @@ static struct attribute *cpuidle_state_default_attrs[] = {
    &attr_power.attr,
    &attr_usage.attr,
    &attr_time.attr,
    + &attr_disable.attr,
    NULL
    };

    @@ -287,8 +310,22 @@ 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


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