On Wed, 17 Dec 2014, Joonsoo Kim wrote:
> + do {
> + tid = this_cpu_read(s->cpu_slab->tid);
> + c = this_cpu_ptr(s->cpu_slab);
> + } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid));
Assembly code produced is a bit weird. I think the compiler undoes what
you wanted to do:
46fb: 49 8b 1e mov (%r14),%rbx
rbx = c =s->cpu_slab?
46fe: 65 4c 8b 6b 08 mov %gs:0x8(%rbx),%r13
r13 = tid
4703: e8 00 00 00 00 callq 4708 <kmem_cache_alloc+0x48>
??
4708: 89 c0 mov %eax,%eax
??
470a: 48 03 1c c5 00 00 00 add 0x0(,%rax,8),%rbx
??
4711: 00
4712: 4c 3b 6b 08 cmp 0x8(%rbx),%r13
tid == c->tid
4716: 49 89 d8 mov %rbx,%r8
4719: 75 e0 jne 46fb <kmem_cache_alloc+0x3b>
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