Stream
使用说明
STREAM 基准测试是一个简单的综合基准测试程序，它测量可持续内存带宽（以 MB/s 为单位）和简单向量内核的相应计算速率。
stream 仅有单个文件，在进行测试时只需要对 stream.c 进行编译即可：
git clone <https://github.com/microseyuyu/STREAM.git>
cd STREAM
gcc -O3 -fopenmp -DN=2000000 -DNTIMES=10 stream.c -o stream
export OMP_NUM_THREADS=8
./stream
参数说明：
- -O3：指定最高编译优化级别，即 3。
- fopenmp：启用OpenMP，适应多处理器环境，更能得到内存带宽实际最大值。开启后，程序默认运行线程为CPU线程数
DN=2000000：指定测试数组a[]、b[]、c[]的大小（Array size）。该值对测试结果影响较大（5.9版本默认值2000000,。若stream.c为5.10版本，参数名变为-DSTREAM_ARRAY_SIZE，默认值10000000）。注意：必须设置测试数组大小远大于CPU 最高级缓存（一般为L3 Cache）的大小，否则就是测试CPU缓存的吞吐性能，而非内存吞吐性能。
- -DNTIMES=10：执行的次数，并从这些结果中选最优值。
- OMP_NUM_THREADS=8 线程数量。
参考结果：
debian@lpi4a:~/Desktop/STREAM$ ./stream
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STREAM version $Revision: 5.10 $
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This system uses 8 bytes per array element.
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***** WARNING: ******
It appears that you set the preprocessor variable N when compiling this code.
This version of the code uses the preprocesor variable STREAM_ARRAY_SIZE to control the array size
Reverting to default value of STREAM_ARRAY_SIZE=10000000
***** WARNING: ******
Array size = 10000000 (elements), Offset = 0 (elements)
Memory per array = 76.3 MiB (= 0.1 GiB).
Total memory required = 228.9 MiB (= 0.2 GiB).
Each kernel will be executed 10 times.
The *best* time for each kernel (excluding the first iteration)
will be used to compute the reported bandwidth.
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Number of Threads requested = 8
Number of Threads counted = 8
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Your clock granularity/precision appears to be 1 microseconds.
Each test below will take on the order of 21622 microseconds.
(= 21622 clock ticks)
Increase the size of the arrays if this shows that
you are not getting at least 20 clock ticks per test.
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WARNING -- The above is only a rough guideline.
For best results, please be sure you know the
precision of your system timer.
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Function Best Rate MB/s Avg time Min time Max time
Copy: 8364.2 0.019258 0.019129 0.019508
Scale: 8291.0 0.019572 0.019298 0.020162
Add: 6223.6 0.038835 0.038563 0.040011
Triad: 6222.5 0.038776 0.038570 0.039470
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Solution Validates: avg error less than 1.000000e-13 on all three arrays
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