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SubjectRe: [PATCH 3/5] perf core: Prepare writing into ring buffer from end
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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.

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