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Subject: Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end
To: pi3orama <pi3orama@163.com>, Peter Zijlstra <peterz@infradead.org>
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CC: <mingo@redhat.com>, <linux-kernel@vger.kernel.org>,
        He Kuang <hekuang@huawei.com>, Alexei Starovoitov <ast@kernel.org>,
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From: "Wangnan (F)" <wangnan0@huawei.com>
Message-ID: <56F88FA9.4080204@huawei.com>
Date: Mon, 28 Mar 2016 09:58:01 +0800
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On 2016/3/28 9:07, Wangnan (F) wrote:
>
>
> 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@infradead.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.
>

Find the reason of these outliners.

If perf and 'test-ring-buffer' are scheduled on different processors,
the performance is bad. I think cache is the main reason.

I will redo the test, bind them to cores on same CPU.

Thank you.