Subject: Re: [RFC][-mm] [1/2] Simple stats for cpu resource controller
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Balaji Rao <balajirrao@gmail.com>
Cc: linux-kernel@vger.kernel.org, menage@google.com, balbir@in.ibm.com,
       containers@lists.osdl.org, dhaval@linux.vnet.ibm.com
In-Reply-To: <200803262348.45219.balajirrao@gmail.com>
References: <200803262348.45219.balajirrao@gmail.com>
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Date: Wed, 26 Mar 2008 20:58:10 +0100
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On Wed, 2008-03-26 at 23:48 +0530, Balaji Rao wrote:
> This patch implements trivial statistics for the cpu controller.
> 
> Signed-off-by: Balaji Rao <balajirrao@gmail.com>
> CC: Balbir Singh <balbir@linux.vnet.ibm.com>
> CC: Dhaval Giani <dhaval@linux.vnet.ibm.com>
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 9fbfa05..eac9333 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -164,10 +164,38 @@ struct cfs_rq;
>  
>  static LIST_HEAD(task_groups);
>  
> +#ifdef CONFIG_CGROUP_SCHED
> +enum cpu_cgroup_stat_index {
> +	CPU_CGROUP_STAT_UTIME, /* Usertime of the task group */
> +	CPU_CGROUP_STAT_STIME, /* Kerneltime of the task group */
> +
> +	CPU_CGROUP_STAT_NSTATS,
> +};
> +
> +struct cpu_cgroup_stat_cpu {
> +	s64 count[CPU_CGROUP_STAT_NSTATS];
> +} ____cacheline_aligned_in_smp;
> +
> +struct cpu_cgroup_stat {
> +	struct cpu_cgroup_stat_cpu cpustat[NR_CPUS];
> +};
> +
> +/* Called under irq disable. */
> +static void __cpu_cgroup_stat_add_safe(struct cpu_cgroup_stat *stat,
> +		enum cpu_cgroup_stat_index idx, int val)

What is safe about this function?

> +{
> +	int cpu = smp_processor_id();
> +
> +	BUG_ON(!irqs_disabled());
> +	stat->cpustat[cpu].count[idx] += val;
> +}
> +#endif
> +
>  /* task group related information */
>  struct task_group {
>  #ifdef CONFIG_CGROUP_SCHED
>  	struct cgroup_subsys_state css;
> +	struct cpu_cgroup_stat stat;
>  #endif
>  
>  #ifdef CONFIG_FAIR_GROUP_SCHED
> @@ -3670,6 +3698,16 @@ void account_user_time(struct task_struct *p, cputime_t cputime)
>  		cpustat->nice = cputime64_add(cpustat->nice, tmp);
>  	else
>  		cpustat->user = cputime64_add(cpustat->user, tmp);
> +
> +	/* Charge the task's group */
> +#ifdef CONFIG_CGROUP_SCHED 
> +	{
> +	struct task_group *tg;
> +	tg = task_group(p);
> +	__cpu_cgroup_stat_add_safe(&tg->stat, CPU_CGROUP_STAT_UTIME,
> +			cputime_to_msecs(cputime));
> +	}
> +#endif
>  }
>  
>  /*
> @@ -3733,6 +3771,15 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
>  		cpustat->idle = cputime64_add(cpustat->idle, tmp);
>  	/* Account for system time used */
>  	acct_update_integrals(p);
> +
> +#ifdef CONFIG_CGROUP_SCHED
> +	{
> +	struct task_group *tg;
> +	tg = task_group(p);
> +	__cpu_cgroup_stat_add_safe(&tg->stat, CPU_CGROUP_STAT_STIME,
> +			cputime_to_msecs(cputime));
> +	}
> +#endif
>  }

So both of these are tick based? The normal CFS [us]time stats are not.

>  /*
> @@ -7939,6 +7986,40 @@ static u64 cpu_shares_read_u64(struct cgroup *cgrp, struct cftype *cft)
>  
>  	return (u64) tg->shares;
>  }
> +
> +static s64 cpu_cgroup_read_stat(struct cpu_cgroup_stat *stat,
> +		enum cpu_cgroup_stat_index idx)
> +{
> +	int cpu;
> +	s64 ret = 0;
> +	for_each_possible_cpu(cpu)
> +		ret += stat->cpustat[cpu].count[idx];
> +	return ret;
> +}
> +
> +static const struct cpu_cgroup_stat_desc {
> +	const char *msg;
> +	u64 unit;
> +} cpu_cgroup_stat_desc[] = {
> +	[CPU_CGROUP_STAT_UTIME] = { "utime", 1, },
> +	[CPU_CGROUP_STAT_STIME] = { "stime", 1, },
> +};
> +
> +static int cpu_cgroup_stats_show(struct cgroup *cgrp, struct cftype *cft,
> +				struct cgroup_map_cb *cb)
> +{
> +	struct task_group *tg = cgroup_tg(cgrp);
> +	struct cpu_cgroup_stat *stat = &tg->stat;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(stat->cpustat[0].count); i++) {
> +		s64 val;
> +		val = cpu_cgroup_read_stat(stat, i);
> +		val *= cpu_cgroup_stat_desc[i].unit;
> +		cb->fill(cb, cpu_cgroup_stat_desc[i].msg, val);
> +	}
> +	return 0;
> +}
>  #endif
>  
>  #ifdef CONFIG_RT_GROUP_SCHED
> @@ -7961,6 +8042,11 @@ static struct cftype cpu_files[] = {
>  		.read_u64 = cpu_shares_read_u64,
>  		.write_u64 = cpu_shares_write_u64,
>  	},
> +
> +	{
> +		.name = "stat",
> +		.read_map = cpu_cgroup_stats_show,
> +	},
>  #endif
>  #ifdef CONFIG_RT_GROUP_SCHED
>  	{
> 
> --
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