Re: [PATCH V2 RFC 3/3] kvm: Check system load and handle different commit cases accordingly

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2012-10-29 at 19:37 +0530, Raghavendra K T wrote:
> +/*
> + * A load of 2048 corresponds to 1:1 overcommit
> + * undercommit threshold is half the 1:1 overcommit
> + * overcommit threshold is 1.75 times of 1:1 overcommit threshold
> + */
> +#define COMMIT_THRESHOLD (FIXED_1)
> +#define UNDERCOMMIT_THRESHOLD (COMMIT_THRESHOLD >> 1)
> +#define OVERCOMMIT_THRESHOLD ((COMMIT_THRESHOLD << 1) -
> (COMMIT_THRESHOLD >> 2))
> +
> +unsigned long kvm_system_load(void)
> +{
> +       unsigned long load;
> +
> +       load = avenrun[0] + FIXED_1/200;
> +       load = load / num_online_cpus();
> +
> +       return load;
> +} 

ARGH.. no that's wrong.. very wrong.

 1) avenrun[] EXPORT_SYMBOL says it should be removed, that's not a
joke.

 2) avenrun[] is a global load, do not ever use a global load measure

 3) avenrun[] has nothing what so ever to do with runqueue lengths,
someone with a gazillion tasks in D state will get a huge load but the
cpu is very idle.