linux-kernel - Re: [PATCH 0/7] slub: Fastpath optimization (especially for RT) V1

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Date:	Thu, 18 Dec 2014 23:41:35 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>, akpm@...uxfoundation.org,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...nel.org>,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH 0/7] slub: Fastpath optimization (especially for RT) V1

2014-12-18 1:10 GMT+09:00 Christoph Lameter <cl@...ux.com>:
> 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:

I checked my compiled code and it seems to be no problem.
gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2

Thanks.

>  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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