Re: [PATCH v3 2/7] sched: accumulate per-cfs_rq cpu usage

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Bharata B Rao <bharata@linux.vnet.ibm.com> [2010-10-12 13:21:09]:

> sched: accumulate per-cfs_rq cpu usage
> 
> From: Paul Turner <pjt@google.com>
> 
> Introduce account_cfs_rq_quota() to account bandwidth usage on the cfs_rq
> level versus task_groups for which bandwidth has been assigned.  This is
> tracked by whether the local cfs_rq->quota_assigned is finite or infinite
> (RUNTIME_INF).
> 
> For cfs_rq's that belong to a bandwidth constrained task_group we introduce
> tg_request_cfs_quota() which attempts to allocate quota from the global pool
> for use locally.  Updates involving the global pool are currently protected
> under cfs_bandwidth->lock, local pools are protected by rq->lock.
> 
> This patch only attempts to assign and track quota, no action is taken in the
> case that cfs_rq->quota_used exceeds cfs_rq->quota_assigned.
> 
> Signed-off-by: Paul Turner <pjt@google.com>
> Signed-off-by: Nikhil Rao <ncrao@google.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  include/linux/sched.h |    4 ++++
>  kernel/sched.c        |   13 +++++++++++++
>  kernel/sched_fair.c   |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  kernel/sysctl.c       |   10 ++++++++++
>  4 files changed, 77 insertions(+)
> 
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1898,6 +1898,10 @@ int sched_rt_handler(struct ctl_table *t
>  		void __user *buffer, size_t *lenp,
>  		loff_t *ppos);
> 
> +#ifdef CONFIG_CFS_BANDWIDTH
> +extern unsigned int sysctl_sched_cfs_bandwidth_slice;
> +#endif
> +
>  extern unsigned int sysctl_sched_compat_yield;
> 
>  #ifdef CONFIG_RT_MUTEXES
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1929,6 +1929,19 @@ static const struct sched_class rt_sched
>   * default: 0.5s
>   */
>  static u64 sched_cfs_bandwidth_period = 500000000ULL;
> +
> +/*
> + * default slice of quota to allocate from global tg to local cfs_rq pool on
> + * each refresh
> + * default: 10ms
> + */
> +unsigned int sysctl_sched_cfs_bandwidth_slice = 10000UL;
> +
> +static inline u64 sched_cfs_bandwidth_slice(void)
> +{
> +	return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
> +}
> +
>  #endif
> 
>  #define sched_class_highest (&rt_sched_class)
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -267,6 +267,16 @@ find_matching_se(struct sched_entity **s
> 
>  #endif	/* CONFIG_FAIR_GROUP_SCHED */
> 
> +#ifdef CONFIG_CFS_BANDWIDTH
> +static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
> +{
> +	return &tg->cfs_bandwidth;
> +}
> +
> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
> +		unsigned long delta_exec);
> +#endif
> +
> 
>  /**************************************************************
>   * Scheduling class tree data structure manipulation methods:
> @@ -547,6 +557,9 @@ static void update_curr(struct cfs_rq *c
>  		cpuacct_charge(curtask, delta_exec);
>  		account_group_exec_runtime(curtask, delta_exec);
>  	}
> +#ifdef CONFIG_CFS_BANDWIDTH
> +	account_cfs_rq_quota(cfs_rq, delta_exec);
> +#endif
>  }
> 
>  static inline void
> @@ -1130,6 +1143,43 @@ static void yield_task_fair(struct rq *r
>  }
> 
>  #ifdef CONFIG_CFS_BANDWIDTH
> +static u64 tg_request_cfs_quota(struct task_group *tg)
> +{
> +	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
> +	u64 delta = 0;
> +
> +	if (cfs_b->runtime > 0 || cfs_b->quota == RUNTIME_INF) {

Quick question for cfs_b->quota == RUNTIME_INF, won't cfs_b->runtime
be always > 0?

> +		raw_spin_lock(&cfs_b->lock);
> +		/*
> +		 * it's possible a bandwidth update has changed the global
> +		 * pool.
> +		 */
> +		if (cfs_b->quota == RUNTIME_INF)
> +			delta = sched_cfs_bandwidth_slice();
> +		else {
> +			delta = min(cfs_b->runtime,
> +					sched_cfs_bandwidth_slice());
> +			cfs_b->runtime -= delta;
> +		}
> +		raw_spin_unlock(&cfs_b->lock);
> +	}
> +	return delta;
> +}
> +
> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
> +		unsigned long delta_exec)
> +{
> +	if (cfs_rq->quota_assigned == RUNTIME_INF)
> +		return;
> +
> +	cfs_rq->quota_used += delta_exec;
> +
> +	if (cfs_rq->quota_used < cfs_rq->quota_assigned)
> +		return;
> +
> +	cfs_rq->quota_assigned += tg_request_cfs_quota(cfs_rq->tg);
> +}
> +
>  static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
>  {
>  	return 1;
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -384,6 +384,16 @@ static struct ctl_table kern_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec,
>  	},
> +#ifdef CONFIG_CFS_BANDWIDTH
> +	{
> +		.procname	= "sched_cfs_bandwidth_slice_us",
> +		.data		= &sysctl_sched_cfs_bandwidth_slice,
> +		.maxlen		= sizeof(unsigned int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &one,
> +	},
> +#endif
>  #ifdef CONFIG_PROVE_LOCKING
>  	{
>  		.procname	= "prove_locking",

-- 
	Three Cheers,
	Balbir