Re: [RFC PATCH] net: frag limit checks need to use percpu_counter_compare

[Stephen Hemminger]

On Thu, 31 Aug 2017 12:20:19 +0200
Jesper Dangaard Brouer <bro...@redhat.com> wrote:

> +static inline bool frag_mem_over_limit(struct netns_frags *nf, int thresh)
>  {
> -     return percpu_counter_read(&nf->mem);
> +     /* When reading counter here, __percpu_counter_compare() call
> +      * will invoke __percpu_counter_sum() when needed.  Which
> +      * depend on num_online_cpus()*batch size, as each CPU can
> +      * potentential can hold a batch count.
> +      *
> +      * With many CPUs this heavier sum operation will
> +      * unfortunately always occur.
> +      */
> +     if (__percpu_counter_compare(&nf->mem, thresh,
> +                                  frag_percpu_counter_batch) > 0)
> +             return true;
> +     else
> +             return false;

You don't need an if() here.

        return __percpu_counter_compare(&nf->mem, thresh,
                                     frag_percpu_counter_batch) > 0;