Re: [PATCH] sched: cpuacct: Use bigger percpu counter batch values for stats counters

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2010-01-18 at 15:41 +1100, Anton Blanchard wrote:
> Hi,
> 
> Another try at this percpu_counter batch issue with CONFIG_VIRT_CPU_ACCOUNTING
> and CONFIG_CGROUP_CPUACCT enabled. Thoughts?

Seems like a good idea, but isn't that batch number rather static? If
so, computing it in some init path would save that multiply on the
actual accounting path.

> 
> Index: linux.trees.git/kernel/sched.c
> ===================================================================
> --- linux.trees.git.orig/kernel/sched.c	2010-01-18 14:27:12.000000000 +1100
> +++ linux.trees.git/kernel/sched.c	2010-01-18 15:21:59.000000000 +1100
> @@ -10894,6 +10894,7 @@ static void cpuacct_update_stats(struct 
>  		enum cpuacct_stat_index idx, cputime_t val)
>  {
>  	struct cpuacct *ca;
> +	int batch;
>  
>  	if (unlikely(!cpuacct_subsys.active))
>  		return;
> @@ -10901,8 +10902,9 @@ static void cpuacct_update_stats(struct 
>  	rcu_read_lock();
>  	ca = task_ca(tsk);
>  
> +	batch = min_t(long, percpu_counter_batch * cputime_one_jiffy, INT_MAX);
>  	do {
> -		percpu_counter_add(&ca->cpustat[idx], val);
> +		__percpu_counter_add(&ca->cpustat[idx], val, batch);
>  		ca = ca->parent;
>  	} while (ca);
>  	rcu_read_unlock();