在 2022/6/1 下午5:50, Alexei Starovoitov 写道:
> On Wed, Jun 1, 2022 at 10:42 AM Feng zhou <[email protected]> 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.
If I'm thinking wrong, please tell me why.