linux-kernel - Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end

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Message-ID: <56F26B29.8040401@huawei.com>
Date:	Wed, 23 Mar 2016 18:08:41 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	<mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	He Kuang <hekuang@...wei.com>,
	Alexei Starovoitov <ast@...nel.org>,
	"Arnaldo Carvalho de Melo" <acme@...hat.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	"Jiri Olsa" <jolsa@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>, <pi3orama@....com>
Subject: Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end



On 2016/3/23 17:50, Peter Zijlstra wrote:
> On Mon, Mar 14, 2016 at 09:59:43AM +0000, Wang Nan wrote:
>> Convert perf_output_begin to __perf_output_begin and make the later
>> function able to write records from the end of the ring buffer.
>> Following commits will utilize the 'backward' flag.
>>
>> This patch doesn't introduce any extra performance overhead since we
>> use always_inline.
> So while I agree that with __always_inline and constant propagation we
> _should_ end up with the same code, we have:
>
> $ size defconfig-build/kernel/events/ring_buffer.o.{pre,post}
>     text    data     bss     dec     hex filename
>     3785       2       0    3787     ecb defconfig-build/kernel/events/ring_buffer.o.pre
>     3673       2       0    3675     e5b defconfig-build/kernel/events/ring_buffer.o.post
>
> The patch actually makes the file shrink.
>
> So I think we still want to have some actual performance numbers.

There are some numbers. You can find them from:

http://lkml.iu.edu/hypermail/linux/kernel/1601.2/03966.html

Thank you.