Re: [PATCH v3] cgroup/freezer: add per freezer duty ratio control

[Jacob Pan]

On Mon, 7 Feb 2011 20:29:29 +0200
"Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote:

> On Mon, Feb 07, 2011 at 10:13:03AM -0800,
> jacob.jun.pan@xxxxxxxxxxxxxxx wrote:
> > From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > 
> > Freezer subsystem is used to manage batch jobs which can start
> > stop at the same time. However, sometime it is desirable to let
> > the kernel manage the freezer state automatically with a given
> > duty ratio.
> > For example, if we want to reduce the time that backgroup apps
> > are allowed to run we can put them into a freezer subsystem and
> > set the kernel to turn them THAWED/FROZEN at given duty ratio.
> > 
> > This patch introduces two file nodes under cgroup
> > freezer.duty_ratio_pct and freezer.period_sec
> > 
> > Usage example: set period to be 5 seconds and frozen duty ratio 90%
> > [root@localhost aoa]# echo 90 > freezer.duty_ratio_pct
> > [root@localhost aoa]# echo 5 > freezer.period_sec
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > ---
> >  Documentation/cgroups/freezer-subsystem.txt |   23 ++++++
> >  kernel/cgroup_freezer.c                     |  109
> > ++++++++++++++++++++++++++- 2 files changed, 130 insertions(+), 2
> > deletions(-)
> > 
> > diff --git a/Documentation/cgroups/freezer-subsystem.txt
> > b/Documentation/cgroups/freezer-subsystem.txt index
> > 41f37fe..2bc1b98 100644 ---
> > a/Documentation/cgroups/freezer-subsystem.txt +++
> > b/Documentation/cgroups/freezer-subsystem.txt @@ -100,3 +100,26 @@
> > things happens: and returns EINVAL)
> >  	3) The tasks that blocked the cgroup from entering the
> > "FROZEN" state disappear from the cgroup's set of tasks.
> > +
> > +In embedded systems, it is desirable to manage group of
> > applications +for power saving. E.g. tasks that are not in the
> > foreground may be +frozen unfrozen periodically to save power
> > without affecting user +experience. In this case, user/management
> > software can attach tasks +into freezer cgroup then specify duty
> > ratio and period that the +managed tasks are allowed to run.
> > +
> > +Usage example:
> > +Assuming freezer cgroup is already mounted, application being
> > managed +are included the "tasks" file node of the given freezer
> > cgroup. +To make the tasks frozen at 90% of the time every 5
> > seconds, do: +
> > +[root@localhost ]# echo 90 > freezer.duty_ratio_pct
> > +[root@localhost ]# echo 5 > freezer.period_sec
> > +
> > +After that, the application in this freezer cgroup will only be
> > +allowed to run at the following pattern.
> > +     __                    __                    __
> > +    |  |<-- 90% frozen -->|  |                  |  |
> > +____|  |__________________|  |__________________|  |_____
> > +
> > +    |<---- 5 seconds ---->|
> > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> > index e7bebb7..928f2ab 100644
> > --- a/kernel/cgroup_freezer.c
> > +++ b/kernel/cgroup_freezer.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/uaccess.h>
> >  #include <linux/freezer.h>
> >  #include <linux/seq_file.h>
> > +#include <linux/kthread.h>
> >  
> >  enum freezer_state {
> >  	CGROUP_THAWED = 0,
> > @@ -28,12 +29,23 @@ enum freezer_state {
> >  	CGROUP_FROZEN,
> >  };
> >  
> > +struct freezer_duty {
> > +	u32 ratio; /* percentage of time frozen */
> > +	u32 period_pct_ms; /* one percent of the period in
> > miliseconds */ +};
> > +
> >  struct freezer {
> >  	struct cgroup_subsys_state css;
> >  	enum freezer_state state;
> > +	struct freezer_duty duty;
> > +	struct task_struct *fkh;
> >  	spinlock_t lock; /* protects _writes_ to state */
> >  };
> >  
> > +static struct task_struct *freezer_task;
> > +static int try_to_freeze_cgroup(struct cgroup *cgroup, struct
> > freezer *freezer); +static void unfreeze_cgroup(struct cgroup
> > *cgroup, struct freezer *freezer); +
> >  static inline struct freezer *cgroup_freezer(
> >  		struct cgroup *cgroup)
> >  {
> > @@ -63,6 +75,35 @@ int cgroup_freezing_or_frozen(struct task_struct
> > *task) return result;
> >  }
> >  
> > +static DECLARE_WAIT_QUEUE_HEAD(freezer_wait);
> > +
> > +static int freezer_kh(void *data)
> > +{
> > +	struct cgroup *cgroup = (struct cgroup *)data;
> > +	struct freezer *freezer = cgroup_freezer(cgroup);
> > +
> > +	do {
> > +		if (freezer->duty.ratio < 100 &&
> > freezer->duty.ratio >= 0 &&
> > +			freezer->duty.period_pct_ms) {
> > +			if (try_to_freeze_cgroup(cgroup, freezer))
> > +				pr_info("cannot freeze\n");
> > +			msleep(freezer->duty.period_pct_ms *
> > +				freezer->duty.ratio);
> > +			unfreeze_cgroup(cgroup, freezer);
> > +			msleep(freezer->duty.period_pct_ms *
> > +				(100 - freezer->duty.ratio));
> > +		} else if (freezer->duty.ratio == 100) {
> > +			if (try_to_freeze_cgroup(cgroup, freezer))
> > +				pr_info("cannot freeze\n");
> > +			sleep_on(&freezer_wait);
> > +		} else {
> > +			sleep_on(&freezer_wait);
> > +			pr_debug("freezer thread wake up\n");
> > +		}
> > +	} while (!kthread_should_stop());
> > +	return 0;
> > +}
> > +
> >  /*
> >   * cgroups_write_string() limits the size of freezer state strings
> > to
> >   * CGROUP_LOCAL_BUFFER_SIZE
> > @@ -150,7 +191,11 @@ static struct cgroup_subsys_state
> > *freezer_create(struct cgroup_subsys *ss, static void
> > freezer_destroy(struct cgroup_subsys *ss, struct cgroup *cgroup)
> >  {
> > -	kfree(cgroup_freezer(cgroup));
> > +	struct freezer *freezer;
> > +
> > +	freezer = cgroup_freezer(cgroup);
> > +	kthread_stop(freezer->fkh);
> > +	kfree(freezer);
> >  }
> >  
> >  /*
> > @@ -282,6 +327,16 @@ static int freezer_read(struct cgroup *cgroup,
> > struct cftype *cft, return 0;
> >  }
> >  
> > +static u64 freezer_read_duty_ratio(struct cgroup *cgroup, struct
> > cftype *cft) +{
> > +	return cgroup_freezer(cgroup)->duty.ratio;
> > +}
> > +
> > +static u64 freezer_read_period(struct cgroup *cgroup, struct
> > cftype *cft) +{
> > +	return cgroup_freezer(cgroup)->duty.period_pct_ms / 10;
> > +}
> > +
> >  static int try_to_freeze_cgroup(struct cgroup *cgroup, struct
> > freezer *freezer) {
> >  	struct cgroup_iter it;
> > @@ -368,19 +423,69 @@ static int freezer_write(struct cgroup
> > *cgroup, return retval;
> >  }
> >  
> > +static int freezer_write_duty_ratio(struct cgroup *cgroup, struct
> > cftype *cft,
> > +		u64 val)
> > +{
> > +	if (!cgroup_lock_live_group(cgroup))
> > +		return -ENODEV;
> > +	cgroup_freezer(cgroup)->duty.ratio = val;
> > +	cgroup_unlock();
> > +	wake_up(&freezer_wait);
> > +
> > +	return 0;
> > +}
> > +
> > +static int freezer_write_period(struct cgroup *cgroup, struct
> > cftype *cft,
> > +		u64 val)
> > +{
> > +	if (!cgroup_lock_live_group(cgroup))
> > +		return -ENODEV;
> > +	cgroup_freezer(cgroup)->duty.period_pct_ms = val * 10;
> 
> 1 second == 1000 millisecond, I guess ;)
here is 1% of 1 second, so 1000 / 100 = 10ms.
> 
> I think better to use milliseconds for the interface.
> 
ok, I will change that back. I don't have preference.

> > +	cgroup_unlock();
> > +	wake_up(&freezer_wait);
> > +
> > +	return 0;
> > +}
> > +
> >  static struct cftype files[] = {
> >  	{
> >  		.name = "state",
> >  		.read_seq_string = freezer_read,
> >  		.write_string = freezer_write,
> >  	},
> > +	{
> > +		.name = "duty_ratio_pct",
> > +		.read_u64 = freezer_read_duty_ratio,
> > +		.write_u64 = freezer_write_duty_ratio,
> > +	},
> > +	{
> > +		.name = "period_sec",
> > +		.read_u64 = freezer_read_period,
> > +		.write_u64 = freezer_write_period,
> > +	},
> > +
> >  };
> >  
> > +#define FREEZER_KH_PREFIX  "freezer_"
> >  static int freezer_populate(struct cgroup_subsys *ss, struct
> > cgroup *cgroup) {
> > +	int ret = 0;
> > +	char thread_name[32];
> > +	struct freezer *freezer;
> > +
> >  	if (!cgroup->parent)
> >  		return 0;
> > -	return cgroup_add_files(cgroup, ss, files,
> > ARRAY_SIZE(files)); +
> > +	freezer = cgroup_freezer(cgroup);
> > +	ret = cgroup_add_files(cgroup, ss, files,
> > ARRAY_SIZE(files)); +
> > +	snprintf(thread_name, 32, "%s%s", FREEZER_KH_PREFIX,
> > +		cgroup->dentry->d_name.name);
> > +	freezer->fkh = kthread_run(freezer_kh, (void *)cgroup,
> > thread_name);
> > +	if (IS_ERR(freezer_task))
> > +		pr_debug("%s failed to create %s\n", __func__,
> > thread_name); +
> > +	return ret;
> 
> Hm.. I think it's waste of resources creates one threads for every
> cgroup. In most cases auto freezing will not be enabled. Can we
> create a thread when it's really needed (ratio != 0 && period != 0)?
good point, i will fix that.
> Can we use delayed workqueues instead of separate thread?
I guess you mean having one private workqueue for all freezer cgroups. I
think it is doable and save memory vs per active freezer kthread, but I
am not sure the effect on concurrency. I will give that a try.

Thanks

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