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

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Message-ID: <56F883D4.6010406@huawei.com>
Date:	Mon, 28 Mar 2016 09:07:32 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	pi3orama <pi3orama@....com>, 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>
Subject: Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end



On 2016/3/27 23:30, pi3orama wrote:
>
> 发自我的 iPhone
>
>> 在 2016年3月27日，下午11:20，Peter Zijlstra <peterz@...radead.org> 写道：
>>
>> On Fri, Mar 25, 2016 at 10:14:36PM +0800, Wangnan (F) wrote:
>>>>> I think you enabled some unusual config options?
>> x86_64-defconfig
>>
>>>> You must enabled CONFIG_OPTIMIZE_INLINING. Now I get similar result:
>> It has that indeed.
>>
>>> After enabling CONFIG_OPTIMIZE_INLINING:
>>>
>>> Test its performance by calling 'close(-1)' for 3000000 times and
>>> use 'perf record -o /dev/null -e raw_syscalls:* test-ring-buffer' to
>>> capture system calls:
>>>
>>>                   MEAN         STDVAR
>>> BASE            800077.1     23448.13
>>> RAWPERF.PRE    2465858.0    603473.70
>>> RAWPERF.POST   2471925.0    609437.60
>>>
>>> Considering the high stdvar, after applying this patch the performance
>>> is not change.
>> Why is your variance so immense? And doesn't that render the
>> measurements pointless?
>>
> For some unknown reason, about
> 10% of these results raises 2 times of normal
> results. Say, "normal results" are about
> 2200000, but those "outliers" are about
> 4400000 (I can't access raw data now).
> Variance becomes much smaller if I remove
> those outliers.

After manually removing outliners (remove 10 outliners from 100 raw
data points in each data set):


                  MEAN         STDVAR
BASE            800077.1     23448.13
RAWPERF.PRE    2265741.0     10421.35
RAWPERF.POST   2269826.0     10507.45

Thank you.

> I guess the outliers is caused by some type
> of lock stepping? No clue about it.
>
> Thank you.
>