From: Chen Gang <chengang@emindsoft.com.cn>
To: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>,
akpm@linux-foundation.org, vbabka@suse.cz,
mgorman@techsingularity.net, gi-oh.kim@profitbricks.com,
iamjoonsoo.kim@lge.com, hillf.zj@alibaba-inc.com,
rientjes@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Chen Gang <gang.chen.5i5j@gmail.com>
Subject: Re: [PATCH] mm: migrate: Use bool instead of int for the return value of PageMovable
Date: Wed, 13 Jul 2016 00:50:12 +0800 [thread overview]
Message-ID: <57851FC4.4000000@emindsoft.com.cn> (raw)
In-Reply-To: <20160712074841.GE14586@dhcp22.suse.cz>
On 7/12/16 15:48, Michal Hocko wrote:
> On Tue 12-07-16 03:47:42, Chen Gang wrote:
> [...]
>> In our case, the 2 output size are same, but under x86_64, the insns are
>> different. After uses bool, it uses push/pop instead of branch, for me,
>> it should be a little better for catching.
>
> The code generated for bool version looks much worse. Look at the fast
> path. Gcc tries to reuse the retq from the fast path in the bool case
> and so it has to push rbp and rbx on the stack.
>
> That being said, gcc doesn't seem to generate a better code for bool so
> I do not think this is really worth it.
>
The code below also merge 3 statements into 1 return statement, although
for me, it is a little more readable, it will generate a little bad code.
That is the reason why the output looks a little bad.
In our case, for gcc 6.0, using bool instead of int for bool function
will get the same output under x86_64.
In our case, for gcc 4.8, using bool instead of int for bool function
will get a little better output under x86_64.
Thanks.
>> The orig:
>>
>> 0000000000001290 <PageMovable>:
>> 1290: 48 8b 47 08 mov 0x8(%rdi),%rax
>> 1294: 83 e0 03 and $0x3,%eax
>> 1297: 48 83 f8 02 cmp $0x2,%rax
>> 129b: 74 03 je 12a0 <__SetPageMovable+0x12a0>
>> 129d: 31 c0 xor %eax,%eax
>> 129f: c3 retq
>> 12a0: 55 push %rbp
>> 12a1: 48 89 e5 mov %rsp,%rbp
>> 12a4: e8 00 00 00 00 callq 12a9 <__SetPageMovable+0x12a9>
>> 12a9: 48 85 c0 test %rax,%rax
>> 12ac: 74 17 je 12c5 <__SetPageMovable+0x12c5>
>> 12ae: 48 8b 50 68 mov 0x68(%rax),%rdx
>> 12b2: 48 85 d2 test %rdx,%rdx
>> 12b5: 74 0e je 12c5 <__SetPageMovable+0x12c5>
>> 12b7: 48 83 7a 68 00 cmpq $0x0,0x68(%rdx)
>> 12bc: b8 01 00 00 00 mov $0x1,%eax
>> 12c1: 74 02 je 12c5 <__SetPageMovable+0x12c5>
>> 12c3: 5d pop %rbp
>> 12c4: c3 retq
>> 12c5: 31 c0 xor %eax,%eax
>> 12c7: 5d pop %rbp
>> 12c8: c3 retq
>> 12c9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
>>
>> The new:
>>
>> 0000000000001290 <PageMovable>:
>> 1290: 48 8b 47 08 mov 0x8(%rdi),%rax
>> 1294: 55 push %rbp
>> 1295: 48 89 e5 mov %rsp,%rbp
>> 1298: 53 push %rbx
>> 1299: 31 db xor %ebx,%ebx
>> 129b: 83 e0 03 and $0x3,%eax
>> 129e: 48 83 f8 02 cmp $0x2,%rax
>> 12a2: 74 05 je 12a9 <__SetPageMovable+0x12a9>
>> 12a4: 89 d8 mov %ebx,%eax
>> 12a6: 5b pop %rbx
>> 12a7: 5d pop %rbp
>> 12a8: c3 retq
>> 12a9: e8 00 00 00 00 callq 12ae <__SetPageMovable+0x12ae>
>> 12ae: 48 85 c0 test %rax,%rax
>> 12b1: 74 f1 je 12a4 <__SetPageMovable+0x12a4>
>> 12b3: 48 8b 40 68 mov 0x68(%rax),%rax
>> 12b7: 48 85 c0 test %rax,%rax
>> 12ba: 74 e8 je 12a4 <__SetPageMovable+0x12a4>
>> 12bc: 48 83 78 68 00 cmpq $0x0,0x68(%rax)
>> 12c1: 0f 95 c3 setne %bl
>> 12c4: 89 d8 mov %ebx,%eax
>> 12c6: 5b pop %rbx
>> 12c7: 5d pop %rbp
>> 12c8: c3 retq
>> 12c9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
>>
>> Thanks.
>> --
>> Chen Gang (陈刚)
>>
>> Managing Natural Environments is the Duty of Human Beings.
>
--
Chen Gang (陈刚)
Managing Natural Environments is the Duty of Human Beings.
next prev parent reply other threads:[~2016-07-12 16:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-09 15:55 [PATCH] mm: migrate: Use bool instead of int for the return value of PageMovable chengang
2016-07-11 0:26 ` Minchan Kim
2016-07-11 19:47 ` Chen Gang
2016-07-12 7:15 ` Vlastimil Babka
2016-07-12 16:42 ` Chen Gang
2016-07-12 7:48 ` Michal Hocko
2016-07-12 16:50 ` Chen Gang [this message]
2016-07-13 7:53 ` Michal Hocko
2016-07-17 0:51 ` Chen Gang
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