[Devel] Re: [PATCH 2/7] res_counter: introduce ratelimiting attributes

[Balbir Singh]

* Andrea Righi <righi.andrea at gmail.com> [2009-04-18 23:38:27]:

> Introduce attributes and functions in res_counter to implement throttling-based
> cgroup subsystems.
> 
> The following attributes have been added to struct res_counter:
>  * @policy:     the limiting policy / algorithm
>  * @capacity:   the maximum capacity of the resource
>  * @timestamp:  timestamp of the last accounted resource request
> 

Units of each of the above would be desirable, without them it is hard
to understand what you are trying to add. What is the unit of
capacity?

> Currently the available policies are: token-bucket and leaky-bucket and the
> attribute @capacity is only used by token-bucket policy (to represent the
> bucket size).
> 
> The following function has been implemented to return the amount of time a
> cgroup should sleep to remain within the defined resource limits.
> 
>   unsigned long long
>   res_counter_ratelimit_sleep(struct res_counter *res, ssize_t val);
> 
> [ Note: only the interfaces needed by the cgroup IO controller are implemented
> right now ]
> 

This is a good RFC, but I would hold off merging till the subsystem
gets in. Having said that I am not convinced about the subsystem
sleeping, if the subsystem is not IO intensive, should it still sleep
because it is over its IO b/w? This might make sense for the CPU
controller, since not having CPU b/w does imply sleeping.

Could you please use the word throttle instead of sleep.


> Signed-off-by: Andrea Righi <righi.andrea at gmail.com>
> ---
>  include/linux/res_counter.h |   69 +++++++++++++++++++++++++++++++----------
>  kernel/res_counter.c        |   72 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 124 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
> index 4c5bcf6..9bed6af 100644
> --- a/include/linux/res_counter.h
> +++ b/include/linux/res_counter.h
> @@ -14,30 +14,36 @@
>   */
> 
>  #include <linux/cgroup.h>
> +#include <linux/jiffies.h>
> 
> -/*
> - * The core object. the cgroup that wishes to account for some
> - * resource may include this counter into its structures and use
> - * the helpers described beyond
> - */
> +/* The various policies that can be used for ratelimiting resources */
> +#define	RATELIMIT_LEAKY_BUCKET	0
> +#define	RATELIMIT_TOKEN_BUCKET	1
> 
> +/**
> + * struct res_counter - the core object to account cgroup resources
> + *
> + * @usage:	the current resource consumption level
> + * @max_usage:	the maximal value of the usage from the counter creation
> + * @limit:	the limit that usage cannot be exceeded
> + * @failcnt:	the number of unsuccessful attempts to consume the resource
> + * @policy:	the limiting policy / algorithm
> + * @capacity:	the maximum capacity of the resource
> + * @timestamp:	timestamp of the last accounted resource request
> + * @lock:	the lock to protect all of the above.
> + *		The routines below consider this to be IRQ-safe
> + *
> + * The cgroup that wishes to account for some resource may include this counter
> + * into its structures and use the helpers described beyond.
> + */
>  struct res_counter {
> -	/*
> -	 * the current resource consumption level
> -	 */
>  	unsigned long long usage;
> -	/*
> -	 * the maximal value of the usage from the counter creation
> -	 */
>  	unsigned long long max_usage;
> -	/*
> -	 * the limit that usage cannot exceed
> -	 */
>  	unsigned long long limit;
> -	/*
> -	 * the number of unsuccessful attempts to consume the resource
> -	 */

Don't understand why res_counter is removed? Am I reading the diff
correctly?

>  	unsigned long long failcnt;
> +	unsigned long long policy;
> +	unsigned long long capacity;
> +	unsigned long long timestamp;
>  	/*
>  	 * the lock to protect all of the above.
>  	 * the routines below consider this to be IRQ-safe
> @@ -84,6 +90,9 @@ enum {
>  	RES_USAGE,
>  	RES_MAX_USAGE,
>  	RES_LIMIT,
> +	RES_POLICY,
> +	RES_TIMESTAMP,
> +	RES_CAPACITY,
>  	RES_FAILCNT,
>  };
> 
> @@ -130,6 +139,15 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
>  	return false;
>  }
> 
> +static inline unsigned long long
> +res_counter_ratelimit_delta_t(struct res_counter *res)
> +{
> +	return (long long)get_jiffies_64() - (long long)res->timestamp;
> +}
> +
> +unsigned long long
> +res_counter_ratelimit_sleep(struct res_counter *res, ssize_t val);
> +
>  /*
>   * Helper function to detect if the cgroup is within it's limit or
>   * not. It's currently called from cgroup_rss_prepare()
> @@ -163,6 +181,23 @@ static inline void res_counter_reset_failcnt(struct res_counter *cnt)
>  	spin_unlock_irqrestore(&cnt->lock, flags);
>  }
> 
> +static inline int
> +res_counter_ratelimit_set_limit(struct res_counter *cnt,
> +			unsigned long long policy,
> +			unsigned long long limit, unsigned long long max)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	cnt->limit = limit;
> +	cnt->capacity = max;
> +	cnt->policy = policy;
> +	cnt->timestamp = get_jiffies_64();
> +	cnt->usage = 0;
> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +	return 0;
> +}
> +
>  static inline int res_counter_set_limit(struct res_counter *cnt,
>  		unsigned long long limit)
>  {
> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> index bf8e753..b62319c 100644
> --- a/kernel/res_counter.c
> +++ b/kernel/res_counter.c
> @@ -9,6 +9,7 @@
> 
>  #include <linux/types.h>
>  #include <linux/parser.h>
> +#include <linux/jiffies.h>
>  #include <linux/fs.h>
>  #include <linux/slab.h>
>  #include <linux/res_counter.h>
> @@ -20,6 +21,8 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent)
>  	spin_lock_init(&counter->lock);
>  	counter->limit = (unsigned long long)LLONG_MAX;
>  	counter->parent = parent;
> +	counter->capacity = (unsigned long long)LLONG_MAX;
> +	counter->timestamp = get_jiffies_64();
>  }
> 
>  int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
> @@ -99,6 +102,12 @@ res_counter_member(struct res_counter *counter, int member)
>  		return &counter->max_usage;
>  	case RES_LIMIT:
>  		return &counter->limit;
> +	case RES_POLICY:
> +		return &counter->policy;
> +	case RES_TIMESTAMP:
> +		return &counter->timestamp;
> +	case RES_CAPACITY:
> +		return &counter->capacity;
>  	case RES_FAILCNT:
>  		return &counter->failcnt;
>  	};
> @@ -163,3 +172,66 @@ int res_counter_write(struct res_counter *counter, int member,
>  	spin_unlock_irqrestore(&counter->lock, flags);
>  	return 0;
>  }
> +
> +static unsigned long long
> +ratelimit_leaky_bucket(struct res_counter *res, ssize_t val)
> +{
> +	unsigned long long delta, t;
> +
> +	res->usage += val;

Is this called from a protected context (w.r.t. res)?

> +	delta = res_counter_ratelimit_delta_t(res);
> +	if (!delta)
> +		return 0;
> +	t = res->usage * USEC_PER_SEC;
> +	t = usecs_to_jiffies(div_u64(t, res->limit));
> +	if (t > delta)
> +		return t - delta;
> +	/* Reset i/o statistics */
> +	res->usage = 0;
> +	res->timestamp = get_jiffies_64();
> +	return 0;
> +}
> +
> +static unsigned long long
> +ratelimit_token_bucket(struct res_counter *res, ssize_t val)
> +{
> +	unsigned long long delta;
> +	long long tok;
> +
> +	res->usage -= val;
> +	delta = jiffies_to_msecs(res_counter_ratelimit_delta_t(res));
> +	res->timestamp = get_jiffies_64();
> +	tok = (long long)res->usage * MSEC_PER_SEC;
> +	if (delta) {
> +		long long max = (long long)res->capacity * MSEC_PER_SEC;
> +
> +		tok += delta * res->limit;
> +		if (tok > max)
> +			tok = max;

Use max_t() here

> +		res->usage = (unsigned long long)div_s64(tok, MSEC_PER_SEC);
> +	}
> +	return (tok < 0) ? msecs_to_jiffies(div_u64(-tok, res->limit)) : 0;
> +}

I don't like the usage of MSEC and USEC for res->usage based on
policy.

> +
> +unsigned long long
> +res_counter_ratelimit_sleep(struct res_counter *res, ssize_t val)
> +{
> +	unsigned long long sleep = 0;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&res->lock, flags);
> +	if (res->limit)
> +		switch (res->policy) {
> +		case RATELIMIT_LEAKY_BUCKET:
> +			sleep = ratelimit_leaky_bucket(res, val);
> +			break;
> +		case RATELIMIT_TOKEN_BUCKET:
> +			sleep = ratelimit_token_bucket(res, val);
> +			break;
> +		default:
> +			WARN_ON(1);
> +			break;
> +		}
> +	spin_unlock_irqrestore(&res->lock, flags);
> +	return sleep;
> +}
> -- 
> 1.5.6.3
> 
> 

-- 
	Balbir
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