Re: [-mm] CPU controller statistics (v5)

[Andrew Morton]

On Wed, 4 Jun 2008 01:35:15 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

> From: Balaji Rao <balajirrao@xxxxxxxxx>
> 
> This is a repost of Balaji's patches at
> http://kerneltrap.org/mailarchive/linux-kernel/2008/5/11/1791504
> I've made changes to the format exported to user space. I've used
> clock_t, since /proc/<pid>/stat uses the same format to export data.
> 
> I've run some basic tests to verify that the patches work.
> 
> Andrew could you please consider them for inclusion if there are no
> objections to this patch. This patch helps fill a void in the controllers
> we have w.r.t. statistics
> 
> The patch is against the latest git.
> 

That is not a changelog.  Please always include a (good) changelog with
each iteration of a patch.

Were all my previous comments addressed?  Most, it seems.

> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index e155aa7..60a25cb 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -293,6 +293,7 @@ int cgroup_is_descendant(const struct cgroup *cgrp);
>  struct cgroup_subsys {
>  	struct cgroup_subsys_state *(*create)(struct cgroup_subsys *ss,
>  						  struct cgroup *cgrp);
> +	void (*initialize)(int early);
>  	void (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
>  	void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
>  	int (*can_attach)(struct cgroup_subsys *ss,
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 15ac0e1..77569d7 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2553,6 +2553,9 @@ int __init cgroup_init_early(void)
>  
>  		if (ss->early_init)
>  			cgroup_init_subsys(ss);
> +
> +		if (ss->initialize)
> +			ss->initialize(1);
>  	}
>  	return 0;
>  }
> @@ -2577,6 +2580,9 @@ int __init cgroup_init(void)
>  		struct cgroup_subsys *ss = subsys[i];
>  		if (!ss->early_init)
>  			cgroup_init_subsys(ss);
> +
> +		if (ss->initialize)
> +			ss->initialize(0);

Can we avoid these tests?  By requiring that cgroup_subsys.initialize()
always be non-zero?  It might make sense, and it might not...

>  	}
>  
>  	/* Add init_css_set to the hash table */
> diff --git a/kernel/sched.c b/kernel/sched.c
> index bfb8ad8..d6df3d3 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -245,11 +245,32 @@ static DEFINE_MUTEX(sched_domains_mutex);
>  struct cfs_rq;
>  
>  static LIST_HEAD(task_groups);
> +#ifdef CONFIG_CGROUP_SCHED
> +#define CPU_CGROUP_STAT_THRESHOLD (1 << 30)
> +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 {
> +	struct percpu_counter cpustat[CPU_CGROUP_STAT_NSTATS];
> +};
> +
> +static void __cpu_cgroup_stat_add(struct cpu_cgroup_stat *stat,
> +		enum cpu_cgroup_stat_index idx, s64 val)
> +{
> +	if (stat)
> +		percpu_counter_add(&stat->cpustat[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
> @@ -3885,6 +3906,16 @@ 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(tg->stat, CPU_CGROUP_STAT_UTIME,
> +				cputime_to_msecs(cputime) * NSEC_PER_MSEC);
> +	}
> +#endif
>  }
>  
>  /*
> @@ -3942,8 +3973,17 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
>  		cpustat->irq = cputime64_add(cpustat->irq, tmp);
>  	else if (softirq_count())
>  		cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
> -	else if (p != rq->idle)
> +	else if (p != rq->idle) {
>  		cpustat->system = cputime64_add(cpustat->system, tmp);
> +#ifdef CONFIG_CGROUP_SCHED
> +		{
> +			struct task_group *tg;
> +			tg = task_group(p);
> +			__cpu_cgroup_stat_add(tg->stat, CPU_CGROUP_STAT_STIME,
> +				cputime_to_msecs(cputime) * NSEC_PER_MSEC);
> +		}
> +#endif

The above two almost-identical code sequences should, I suggest, be
broken out into a standalone helper function, which has two
implementations, the CONFIG_CGROUP_SCHED=n version of which is a
do-nothing stub, in the usual fashion.

I suggested this last time.

> +	}
>  	else if (atomic_read(&rq->nr_iowait) > 0)
>  		cpustat->iowait = cputime64_add(cpustat->iowait, tmp);
>  	else
> @@ -8325,6 +8365,24 @@ unsigned long sched_group_shares(struct task_group *tg)
>  }
>  #endif
>  
> +static s64 cpu_cgroup_read_stat(struct cpu_cgroup_stat *stat,
> +		enum cpu_cgroup_stat_index idx)
> +{
> +	if (stat)
> +		return nsec_to_clock_t(
> +				percpu_counter_read(&stat->cpustat[idx]));
> +
> +	return 0;
> +}

ick at the code layout.  How about this:

	if (!stat)
		return 0;
	return nsec_to_clock_t(percpu_counter_read(&stat->cpustat[idx]));

?

> +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, },
> +};
> +
>  #ifdef CONFIG_RT_GROUP_SCHED
>  /*
>   * Ensure that the real time constraints are schedulable.
> @@ -8551,10 +8609,41 @@ static inline struct task_group *cgroup_tg(struct cgroup *cgrp)
>  			    struct task_group, css);
>  }
>  
> +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 < CPU_CGROUP_STAT_NSTATS; i++) {

Please prefer to put a blank line between end-of-locals and
start-of-code.  It does make the code somewhat easier to read.


> +		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;
> +}
> +
> +static void cpu_cgroup_initialize(int early)
> +{
> +	int i;
> +	struct cpu_cgroup_stat *stat;
> +
> +	if (!early) {

like that.

> +		stat = kmalloc(sizeof(struct cpu_cgroup_stat)
> +				, GFP_KERNEL);
> +		for (i = 0; i < CPU_CGROUP_STAT_NSTATS; i++)
> +			percpu_counter_init(
> +					&stat->cpustat[i], 0);

Suppose the kmalloc failed?

> +		init_task_group.stat = stat;
> +	}
> +}

more icky layout, and what's that comma doing there?

Again, please use a bit of thought rather than blindly whacking in
newlines everywhere.

static void cpu_cgroup_initialize(int early)
{
	int i;
	struct cpu_cgroup_stat *stat;

	if (early)
		return;

	stat = kmalloc(sizeof(struct cpu_cgroup_stat), GFP_KERNEL);
	for (i = 0; i < CPU_CGROUP_STAT_NSTATS; i++)
		percpu_counter_init(&stat->cpustat[i], 0);
	init_task_group.stat = stat;
}

is better, yes?


Also, if this code is likely to be executed with any frequency then the
test of `early' could be inlined:

static inline void cpu_cgroup_initialize(int early)
{
	if (unlikely(!early))
		__cpu_cgroup_initialize();
}

yes?


>  static struct cgroup_subsys_state *
>  cpu_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cgrp)
>  {
>  	struct task_group *tg, *parent;
> +	int i;
>  
>  	if (!cgrp->parent) {
>  		/* This is early initialization for the top cgroup */
> @@ -8567,6 +8656,10 @@ cpu_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cgrp)
>  	if (IS_ERR(tg))
>  		return ERR_PTR(-ENOMEM);
>  
> +	tg->stat = kmalloc(sizeof(struct cpu_cgroup_stat), GFP_KERNEL);
> +	for (i = 0; i < CPU_CGROUP_STAT_NSTATS; i++)
> +		percpu_counter_init(&tg->stat->cpustat[i], 0);

Which will crash the machine if the kmalloc failed.



c'mon guys, that wasn't a great effort.
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