Re: [RFC PATCH] net: frag limit checks need to use percpu_counter_compare
flat view
From: Stephen Hemminger <stephen@networkplumber.org>
Date: 2017-08-31 15:58:06
On Thu, 31 Aug 2017 12:20:19 +0200 Jesper Dangaard Brouer [off-list ref] wrote:
quoted hunk ↗ jump to hunk
+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;