Re: [Patch 2/7] Add sysctl for schedstats

Nick Piggin
2006-02-27T09:17:47Z

Shailabh Nagar wrote:
> schedstats-sysctl.patch
>
> Add sysctl option for controlling schedstats collection
> dynamically. Delay accounting leverages schedstats for
> cpu delay statistics.
>

I'd sort of rather not tie this in with schedstats if possible.
Schedstats adds a reasonable amount of cache footprint and
branches in hot paths. Most of schedstats stuff is something that
hardly anyone will use.

Sure you can share common code though...

>
> Index: linux-2.6.16-rc4/kernel/sched.c
> ===================================================================
> --- linux-2.6.16-rc4.orig/kernel/sched.c 2006-02-27 01:20:04.000000000 -0500
> +++ linux-2.6.16-rc4/kernel/sched.c 2006-02-27 01:52:52.000000000 -0500
> @@ -382,11 +382,56 @@ static inline void task_rq_unlock(runque
> }
>
> #ifdef CONFIG_SCHEDSTATS
> +
> +int schedstats_sysctl = 0; /* schedstats turned off by default */

Should be read mostly.

> +static DEFINE_PER_CPU(int, schedstats) = 0;
> +

When the above is in the read mostly section, you won't need this at all.

You don't intend to switch the sysctl with great frequency, do you?

> +static void schedstats_set(int val)
> +{
> + int i;
> + static spinlock_t schedstats_lock = SPIN_LOCK_UNLOCKED;
> +
> + spin_lock(&schedstats_lock);
> + schedstats_sysctl = val;
> + for (i = 0; i < NR_CPUS; i++)
> + per_cpu(schedstats, i) = val;
> + spin_unlock(&schedstats_lock);
> +}
> +
> +static int __init schedstats_setup_enable(char *str)
> +{
> + schedstats_sysctl = 1;
> + schedstats_set(schedstats_sysctl);
> + return 1;
> +}
> +
> +__setup("schedstats", schedstats_setup_enable);
> +
> +int schedstats_sysctl_handler(ctl_table *table, int write, struct file *filp,
> + void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> + int ret, prev = schedstats_sysctl;
> + struct task_struct *g, *t;
> +
> + ret = proc_dointvec(table, write, filp, buffer, lenp, ppos);
> + if ((ret != 0) || (prev == schedstats_sysctl))
> + return ret;
> + if (schedstats_sysctl) {
> + read_lock(&tasklist_lock);
> + do_each_thread(g, t) {
> + memset(&t->sched_info, 0, sizeof(t->sched_info));
> + } while_each_thread(g, t);
> + read_unlock(&tasklist_lock);
> + }
> + schedstats_set(schedstats_sysctl);

You don't clear the rq's schedstats stuff here.

And clearing this at all is not really needed for the schedstats interface.
You have a timestamp and a set of accumulated values, so it is easy to work
out deltas. So do you need this?

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