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SubjectRe: [PATCH V2] idle/intel_powerclamp: Redesign idle injection to use bandwidth control mechanism
Hi Steven,

On 02/09/2015 01:02 PM, Steven Noonan wrote:
> On Sun, Feb 8, 2015 at 8:49 PM, Preeti U Murthy
> <preeti@linux.vnet.ibm.com> wrote:
>> The powerclamp driver injects idle periods to stay within the thermal constraints.
>> The driver does a fake idle by spawning per-cpu threads that call the mwait
>> instruction. This behavior of fake idle can confuse the other kernel subsystems.
>> For instance it calls into the nohz tick handlers, which are meant to be called
>> only by the idle thread. It sets the state of the tick in each cpu to idle and
>> stops the tick, when there are tasks on the runqueue. As a result the callers of
>> idle_cpu()/ tick_nohz_tick_stopped() see different states of the cpu; while the
>> former thinks that the cpu is busy, the latter thinks that it is idle. The outcome
>> may be inconsistency in the scheduler/nohz states which can lead to serious
>> consequences. One of them was reported on this thread:
>> https://lkml.org/lkml/2014/12/11/365.
>>
>> Thomas posted out a patch to disable the powerclamp driver from calling into the
>> tick nohz code which has taken care of the above regression for the moment. However
>> powerclamp driver as a result, will not be able to inject idle periods due to the
>> presence of periodic ticks. With the current design of fake idle, we cannot move
>> towards a better solution.
>> https://lkml.org/lkml/2014/12/18/169
>>
>> This patch aims at removing the concept of fake idle and instead makes the cpus
>> truly idle by throttling the runqueues during the idle injection periods. The situation
>> is in fact very similar to throttling of cfs_rqs when they exceed their bandwidths.
>> The idle injection metrics can be mapped to the bandwidth control metrics 'quota' and
>> 'period' to achieve the same result. When the powerclamping is begun or when the
>> clamping controls have been modified, the bandwidth for the root task group is set.
>> The 'quota' will be the amount of time that the system needs to be busy and 'period'
>> will be the sum of this busy duration and the idle duration as calculated by the driver.
>> This gets rid of per-cpu kthreads, control cpu, hotplug notifiers and clamping mask since
>> the thread starting powerclamping will set the bandwidth and throttling of all cpus will
>> automatically fall in place. None of the other cpus need be bothered about this. This
>> simplifies the design of the driver.
>>
>> Of course this is only if the idle injection metrics can be conveniently transformed
>> into bandwidth control metrics. There are a couple of other primary concerns around if
>> doing the below two in this patch is valid.
>> a. This patch exports the functions to set the quota and period of task groups.
>> b. This patch removes the constraint of not being able to set the root task grp's bandwidth.
>>
>> Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
>
> This doesn't compile.

Thanks for reporting this! I realized that I had not compiled in the powerclamp driver
as a module while compile testing it. I was focusing on the issues with the design and
failed to cross verify this. Apologies for the inconvenience.

Find the diff compile tested below.

I also realized that clamp_cpus() that sets the bandwidth cannot be called from
multiple places. Currently I am calling it from end_powerclamp(), when the user changes the
idle clamping duration and from a queued timer. This will require synchronization between
callers which is not really called for. The queued wakeup_timer alone can re-evaluate the
clamping metrics after every throttle-unthrottle period and this should suffice as far
as I can see. Thoughts ?

Regards
Preeti U Murthy

----------------------------------------------------------------------------------

V2 of intel_powerclamp driver

From: Preeti U Murthy <preeti@linux.vnet.ibm.com>


---
drivers/thermal/Kconfig | 1
drivers/thermal/intel_powerclamp.c | 301 ++++++++++--------------------------
include/linux/sched.h | 9 +
kernel/sched/core.c | 6 -
kernel/sched/sched.h | 5 -
5 files changed, 95 insertions(+), 227 deletions(-)

diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index af40db0..4b7cd02 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -233,6 +233,7 @@ config INTEL_POWERCLAMP
depends on THERMAL
depends on X86
depends on CPU_SUP_INTEL
+ select CFS_BANDWIDTH
help
Enable this to enable Intel PowerClamp idle injection driver. This
enforce idle time which results in more package C-state residency. The
diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
index 6ceebd6..4bd07bb 100644
--- a/drivers/thermal/intel_powerclamp.c
+++ b/drivers/thermal/intel_powerclamp.c
@@ -51,6 +51,7 @@
#include <linux/debugfs.h>
#include <linux/seq_file.h>
#include <linux/sched/rt.h>
+#include <linux/sched.h>

#include <asm/nmi.h>
#include <asm/msr.h>
@@ -78,20 +79,18 @@ static struct dentry *debug_dir;
static unsigned int set_target_ratio;
static unsigned int current_ratio;
static bool should_skip;
+static unsigned int count = 0;
static bool reduce_irq;
static atomic_t idle_wakeup_counter;
-static unsigned int control_cpu; /* The cpu assigned to collect stat and update
- * control parameters. default to BSP but BSP
- * can be offlined.
- */
static bool clamping;

+/* Timer that evaluates bandwidth reset if clamping knobs have changed */
+static void clamp_timer_fn(unsigned long foo);
+DEFINE_TIMER(wakeup_timer, clamp_timer_fn, 0, 0);
+
+static void clamp_cpus(void);

-static struct task_struct * __percpu *powerclamp_thread;
static struct thermal_cooling_device *cooling_dev;
-static unsigned long *cpu_clamping_mask; /* bit map for tracking per cpu
- * clamping thread
- */

static unsigned int duration;
static unsigned int pkg_cstate_ratio_cur;
@@ -163,7 +162,7 @@ static int window_size_set(const char *arg, const struct kernel_param *kp)
smp_mb();

exit_win:
-
+ clamp_cpus();
return ret;
}

@@ -256,10 +255,6 @@ static u64 pkg_state_counter(void)
return count;
}

-static void noop_timer(unsigned long foo)
-{
- /* empty... just the fact that we get the interrupt wakes us up */
-}

static unsigned int get_compensation(int ratio)
{
@@ -362,100 +357,77 @@ static bool powerclamp_adjust_controls(unsigned int target_ratio,
return set_target_ratio + guard <= current_ratio;
}

-static int clamp_thread(void *arg)
+static void clamp_cpus(void)
{
- int cpunr = (unsigned long)arg;
- DEFINE_TIMER(wakeup_timer, noop_timer, 0, 0);
- static const struct sched_param param = {
- .sched_priority = MAX_USER_RT_PRIO/2,
- };
- unsigned int count = 0;
unsigned int target_ratio;
+ u64 quota, period;
+ int sleeptime;
+ unsigned long target_jiffies;
+ unsigned int guard;
+ unsigned int compensation;
+ int interval; /* jiffies to sleep for each attempt */
+ unsigned int duration_jiffies;
+ unsigned int window_size_now;
+
+again:
+ if (clamping == false)
+ goto out;
+
+ quota = RUNTIME_INF;
+ period = NSEC_PER_SEC;
+ compensation = 0;
+ duration_jiffies = msecs_to_jiffies(duration);
+ /*
+ * make sure user selected ratio does not take effect until
+ * the next round. adjust target_ratio if user has changed
+ * target such that we can converge quickly.
+ */
+ target_ratio = set_target_ratio;
+ guard = 1 + target_ratio/20;
+ window_size_now = window_size;

- set_bit(cpunr, cpu_clamping_mask);
- set_freezable();
- init_timer_on_stack(&wakeup_timer);
- sched_setscheduler(current, SCHED_FIFO, &param);
-
- while (true == clamping && !kthread_should_stop() &&
- cpu_online(cpunr)) {
- int sleeptime;
- unsigned long target_jiffies;
- unsigned int guard;
- unsigned int compensation = 0;
- int interval; /* jiffies to sleep for each attempt */
- unsigned int duration_jiffies = msecs_to_jiffies(duration);
- unsigned int window_size_now;
-
- try_to_freeze();
- /*
- * make sure user selected ratio does not take effect until
- * the next round. adjust target_ratio if user has changed
- * target such that we can converge quickly.
- */
- target_ratio = set_target_ratio;
- guard = 1 + target_ratio/20;
- window_size_now = window_size;
- count++;
-
- /*
- * systems may have different ability to enter package level
- * c-states, thus we need to compensate the injected idle ratio
- * to achieve the actual target reported by the HW.
- */
- compensation = get_compensation(target_ratio);
- interval = duration_jiffies*100/(target_ratio+compensation);
-
- /* align idle time */
- target_jiffies = roundup(jiffies, interval);
- sleeptime = target_jiffies - jiffies;
- if (sleeptime <= 0)
- sleeptime = 1;
- schedule_timeout_interruptible(sleeptime);
- /*
- * only elected controlling cpu can collect stats and update
- * control parameters.
- */
- if (cpunr == control_cpu && !(count%window_size_now)) {
- should_skip =
- powerclamp_adjust_controls(target_ratio,
- guard, window_size_now);
- smp_mb();
- }
-
- if (should_skip)
- continue;
-
- target_jiffies = jiffies + duration_jiffies;
- mod_timer(&wakeup_timer, target_jiffies);
- if (unlikely(local_softirq_pending()))
- continue;
- /*
- * stop tick sched during idle time, interrupts are still
- * allowed. thus jiffies are updated properly.
- */
- preempt_disable();
- /* mwait until target jiffies is reached */
- while (time_before(jiffies, target_jiffies)) {
- unsigned long ecx = 1;
- unsigned long eax = target_mwait;
-
- /*
- * REVISIT: may call enter_idle() to notify drivers who
- * can save power during cpu idle. same for exit_idle()
- */
- local_touch_nmi();
- stop_critical_timings();
- mwait_idle_with_hints(eax, ecx);
- start_critical_timings();
- atomic_inc(&idle_wakeup_counter);
- }
- preempt_enable();
+ /*
+ * systems may have different ability to enter package level
+ * c-states, thus we need to compensate the injected idle ratio
+ * to achieve the actual target reported by the HW.
+ */
+ compensation = get_compensation(target_ratio);
+ interval = duration_jiffies*100/(target_ratio+compensation);
+
+ /* align idle time */
+ target_jiffies = roundup(jiffies, interval);
+ sleeptime = target_jiffies - jiffies;
+ if (sleeptime <= 0)
+ sleeptime = 1;
+
+ if (!(count%window_size_now)) {
+ should_skip =
+ powerclamp_adjust_controls(target_ratio,
+ guard, window_size_now);
+ smp_mb();
}
- del_timer_sync(&wakeup_timer);
- clear_bit(cpunr, cpu_clamping_mask);

- return 0;
+ if (should_skip)
+ goto again;
+
+ target_jiffies = jiffies + sleeptime + duration_jiffies;
+ mod_timer(&wakeup_timer, target_jiffies);
+ if (unlikely(local_softirq_pending()))
+ goto again;
+
+ quota = jiffies_to_usecs(sleeptime);
+ period = jiffies_to_usecs(sleeptime + duration_jiffies);
+
+out:
+ tg_set_cfs_quota(&root_task_group, quota);
+ tg_set_cfs_period(&root_task_group, period);
+}
+
+static void clamp_timer_fn(unsigned long foo)
+{
+ /* Evaluate to see if clamping controls need to be adjusted */
+ count++;
+ clamp_cpus();
}

/*
@@ -501,8 +473,7 @@ static void poll_pkg_cstate(struct work_struct *dummy)

static int start_power_clamp(void)
{
- unsigned long cpu;
- struct task_struct *thread;
+ clamping = true;

/* check if pkg cstate counter is completely 0, abort in this case */
if (!has_pkg_state_counter()) {
@@ -511,108 +482,21 @@ static int start_power_clamp(void)
}

set_target_ratio = clamp(set_target_ratio, 0U, MAX_TARGET_RATIO - 1);
- /* prevent cpu hotplug */
- get_online_cpus();
-
- /* prefer BSP */
- control_cpu = 0;
- if (!cpu_online(control_cpu))
- control_cpu = smp_processor_id();

- clamping = true;
schedule_delayed_work(&poll_pkg_cstate_work, 0);
-
- /* start one thread per online cpu */
- for_each_online_cpu(cpu) {
- struct task_struct **p =
- per_cpu_ptr(powerclamp_thread, cpu);
-
- thread = kthread_create_on_node(clamp_thread,
- (void *) cpu,
- cpu_to_node(cpu),
- "kidle_inject/%ld", cpu);
- /* bind to cpu here */
- if (likely(!IS_ERR(thread))) {
- kthread_bind(thread, cpu);
- wake_up_process(thread);
- *p = thread;
- }
-
- }
- put_online_cpus();
+ clamp_cpus();

return 0;
}

static void end_power_clamp(void)
{
- int i;
- struct task_struct *thread;
-
clamping = false;
- /*
- * make clamping visible to other cpus and give per cpu clamping threads
- * sometime to exit, or gets killed later.
- */
- smp_mb();
- msleep(20);
- if (bitmap_weight(cpu_clamping_mask, num_possible_cpus())) {
- for_each_set_bit(i, cpu_clamping_mask, num_possible_cpus()) {
- pr_debug("clamping thread for cpu %d alive, kill\n", i);
- thread = *per_cpu_ptr(powerclamp_thread, i);
- kthread_stop(thread);
- }
- }
-}

-static int powerclamp_cpu_callback(struct notifier_block *nfb,
- unsigned long action, void *hcpu)
-{
- unsigned long cpu = (unsigned long)hcpu;
- struct task_struct *thread;
- struct task_struct **percpu_thread =
- per_cpu_ptr(powerclamp_thread, cpu);
-
- if (false == clamping)
- goto exit_ok;
-
- switch (action) {
- case CPU_ONLINE:
- thread = kthread_create_on_node(clamp_thread,
- (void *) cpu,
- cpu_to_node(cpu),
- "kidle_inject/%lu", cpu);
- if (likely(!IS_ERR(thread))) {
- kthread_bind(thread, cpu);
- wake_up_process(thread);
- *percpu_thread = thread;
- }
- /* prefer BSP as controlling CPU */
- if (cpu == 0) {
- control_cpu = 0;
- smp_mb();
- }
- break;
- case CPU_DEAD:
- if (test_bit(cpu, cpu_clamping_mask)) {
- pr_err("cpu %lu dead but powerclamping thread is not\n",
- cpu);
- kthread_stop(*percpu_thread);
- }
- if (cpu == control_cpu) {
- control_cpu = smp_processor_id();
- smp_mb();
- }
- }
-
-exit_ok:
- return NOTIFY_OK;
+ clamp_cpus();
+ del_timer_sync(&wakeup_timer);
}

-static struct notifier_block powerclamp_cpu_notifier = {
- .notifier_call = powerclamp_cpu_callback,
-};
-
static int powerclamp_get_max_state(struct thermal_cooling_device *cdev,
unsigned long *state)
{
@@ -656,6 +540,7 @@ static int powerclamp_set_cur_state(struct thermal_cooling_device *cdev,
}

exit_set:
+ clamp_cpus();
return ret;
}

@@ -716,7 +601,6 @@ static int powerclamp_debug_show(struct seq_file *m, void *unused)
{
int i = 0;

- seq_printf(m, "controlling cpu: %d\n", control_cpu);
seq_printf(m, "pct confidence steady dynamic (compensation)\n");
for (i = 0; i < MAX_TARGET_RATIO; i++) {
seq_printf(m, "%d\t%lu\t%lu\t%lu\n",
@@ -762,33 +646,20 @@ file_error:
static int powerclamp_init(void)
{
int retval;
- int bitmap_size;
-
- bitmap_size = BITS_TO_LONGS(num_possible_cpus()) * sizeof(long);
- cpu_clamping_mask = kzalloc(bitmap_size, GFP_KERNEL);
- if (!cpu_clamping_mask)
- return -ENOMEM;

/* probe cpu features and ids here */
retval = powerclamp_probe();
if (retval)
- goto exit_free;
+ goto exit;

/* set default limit, maybe adjusted during runtime based on feedback */
window_size = 2;
- register_hotcpu_notifier(&powerclamp_cpu_notifier);
-
- powerclamp_thread = alloc_percpu(struct task_struct *);
- if (!powerclamp_thread) {
- retval = -ENOMEM;
- goto exit_unregister;
- }

cooling_dev = thermal_cooling_device_register("intel_powerclamp", NULL,
&powerclamp_cooling_ops);
if (IS_ERR(cooling_dev)) {
retval = -ENODEV;
- goto exit_free_thread;
+ goto exit;
}

if (!duration)
@@ -798,23 +669,15 @@ static int powerclamp_init(void)

return 0;

-exit_free_thread:
- free_percpu(powerclamp_thread);
-exit_unregister:
- unregister_hotcpu_notifier(&powerclamp_cpu_notifier);
-exit_free:
- kfree(cpu_clamping_mask);
+exit:
return retval;
}
module_init(powerclamp_init);

static void powerclamp_exit(void)
{
- unregister_hotcpu_notifier(&powerclamp_cpu_notifier);
end_power_clamp();
- free_percpu(powerclamp_thread);
thermal_cooling_device_unregister(cooling_dev);
- kfree(cpu_clamping_mask);

cancel_delayed_work_sync(&poll_pkg_cstate_work);
debugfs_remove_recursive(debug_dir);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8db31ef..2493942 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -163,6 +163,11 @@ extern void get_avenrun(unsigned long *loads, unsigned long offset, int shift);
load += n*(FIXED_1-exp); \
load >>= FSHIFT;

+/*
+ * single value that denotes runtime == period, ie unlimited time.
+ */
+#define RUNTIME_INF ((u64)~0ULL)
+
extern unsigned long total_forks;
extern int nr_threads;
DECLARE_PER_CPU(unsigned long, process_counts);
@@ -3002,6 +3007,10 @@ extern long sched_getaffinity(pid_t pid, struct cpumask *mask);

#ifdef CONFIG_CGROUP_SCHED
extern struct task_group root_task_group;
+#ifdef CONFIG_CFS_BANDWIDTH
+extern int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us);
+extern int tg_set_cfs_period(struct task_group *tg, long cfs_period_us);
+#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_CGROUP_SCHED */

extern int task_can_switch_user(struct user_struct *up,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e628cb1..7471b06 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7097,6 +7097,7 @@ int in_sched_functions(unsigned long addr)
* Every task in system belongs to this group at bootup.
*/
struct task_group root_task_group;
+EXPORT_SYMBOL_GPL(root_task_group);
LIST_HEAD(task_groups);
#endif

@@ -8059,9 +8060,6 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
int i, ret = 0, runtime_enabled, runtime_was_enabled;
struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;

- if (tg == &root_task_group)
- return -EINVAL;
-
/*
* Ensure we have at some amount of bandwidth every period. This is
* to prevent reaching a state of large arrears when throttled via
@@ -8141,6 +8139,7 @@ int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)

return tg_set_cfs_bandwidth(tg, period, quota);
}
+EXPORT_SYMBOL_GPL(tg_set_cfs_quota);

long tg_get_cfs_quota(struct task_group *tg)
{
@@ -8164,6 +8163,7 @@ int tg_set_cfs_period(struct task_group *tg, long cfs_period_us)

return tg_set_cfs_bandwidth(tg, period, quota);
}
+EXPORT_SYMBOL_GPL(tg_set_cfs_period);

long tg_get_cfs_period(struct task_group *tg)
{
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9a2a45c..20493e4 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -72,11 +72,6 @@ extern void update_cpu_load_active(struct rq *this_rq);
* These are the 'tuning knobs' of the scheduler:
*/

-/*
- * single value that denotes runtime == period, ie unlimited time.
- */
-#define RUNTIME_INF ((u64)~0ULL)
-
static inline int fair_policy(int policy)
{
return policy == SCHED_NORMAL || policy == SCHED_BATCH;


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