Messages in this thread | | | Date | Thu, 2 Jun 2022 11:27:49 +0800 | Subject | Re: Re: [PATCH v4 1/2] bpf: avoid grabbing spin_locks of all cpus when no free elems | From | Feng Zhou <> |
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在 2022/6/1 下午7:35, Alexei Starovoitov 写道: > On Wed, Jun 1, 2022 at 1:11 PM Feng Zhou <zhoufeng.zf@bytedance.com> wrote: >> 在 2022/6/1 下午5:50, Alexei Starovoitov 写道: >>> On Wed, Jun 1, 2022 at 10:42 AM Feng zhou <zhoufeng.zf@bytedance.com> wrote: >>>> static inline void ___pcpu_freelist_push(struct pcpu_freelist_head *head, >>>> @@ -130,14 +134,19 @@ static struct pcpu_freelist_node *___pcpu_freelist_pop(struct pcpu_freelist *s) >>>> orig_cpu = cpu = raw_smp_processor_id(); >>>> while (1) { >>>> head = per_cpu_ptr(s->freelist, cpu); >>>> + if (READ_ONCE(head->is_empty)) >>>> + goto next_cpu; >>>> raw_spin_lock(&head->lock); >>>> node = head->first; >>>> if (node) { >>> extra bool is unnecessary. >>> just READ_ONCE(head->first) >> As for why to add is_empty instead of directly judging head->first, my >> understanding is this, head->first is frequently modified during updating >> map, which will lead to invalid other cpus's cache, and is_empty is after >> freelist having no free elems will be changed, the performance will be >> better. > maybe. pls benchmark it. > imo wasting a bool for the corner case is not a good trade off.
Yes, I will do and post the results as soon as possible, Thanks.
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