评估DDR通道数¶
整体思路：获取实际的峰峰值总带宽T，按照DDR型号及频率，确认单通道带宽t，channel数 = T/t
获取峰峰值带宽使用jeffhammond/STREAM stream官方文档 网友对于stream的解读 获取DDR型号及频率，使用 dmidecode --type memory 命令
获取峰峰值带宽¶
确认工具能够正常运行¶
git clone https://github.com/jeffhammond/STREAM.git
cd STREAM
make stream_c.exe
./stream_c.exe
获取测试机L3 Cache的大小¶
方法一：
~/workspace$ getconf -a | grep CACHE
LEVEL1_ICACHE_SIZE 32768
LEVEL1_ICACHE_ASSOC 8
LEVEL1_ICACHE_LINESIZE 64
LEVEL1_DCACHE_SIZE 32768
LEVEL1_DCACHE_ASSOC 8
LEVEL1_DCACHE_LINESIZE 64
LEVEL2_CACHE_SIZE 1048576
LEVEL2_CACHE_ASSOC 16
LEVEL2_CACHE_LINESIZE 64
LEVEL3_CACHE_SIZE 28835840
LEVEL3_CACHE_ASSOC 11
LEVEL3_CACHE_LINESIZE 64
LEVEL4_CACHE_SIZE 0
LEVEL4_CACHE_ASSOC 0
LEVEL4_CACHE_LINESIZE 0
方法二：
sudo dmidecode -t cache
方法三：
lscpu
根据L3 Cache大小修改STREAM_ARRAY_SIZE¶
可以直接修改stream.c中的STREAM_ARRAY_SIZE，也可以在make的时候 -DSTREAM_ARRAY_SIZE 来进行修改
STREAM_ARRAY_SIZE = LEVEL3_CACHE_SIZE * 4
因为L3 Cache获取到的是28MB, 那么STREAM_ARRAY_SIZE设置为120MB比较合适
再次编译运行stream¶
-------------------------------------------------------------
STREAM version $Revision: 5.10 $
-------------------------------------------------------------
This system uses 8 bytes per array element.
-------------------------------------------------------------
Array size = 120000000 (elements), Offset = 0 (elements)
Memory per array = 915.5 MiB (= 0.9 GiB).
Total memory required = 2746.6 MiB (= 2.7 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.
-------------------------------------------------------------
Number of Threads requested = 80
Number of Threads counted = 80
-------------------------------------------------------------
Your clock granularity/precision appears to be 1 microseconds.
Each test below will take on the order of 31161 microseconds.
(= 31161 clock ticks)
Increase the size of the arrays if this shows that
you are not getting at least 20 clock ticks per test.
-------------------------------------------------------------
WARNING -- The above is only a rough guideline.
For best results, please be sure you know the
precision of your system timer.
-------------------------------------------------------------
Function Best Rate MB/s Avg time Min time Max time
Copy: 44672.0 0.055925 0.042980 0.101943
Scale: 50632.9 0.046314 0.037920 0.062966
Add: 57618.5 0.056867 0.049984 0.069840
Triad: 57517.2 0.060273 0.050072 0.096959
-------------------------------------------------------------
Solution Validates: avg error less than 1.000000e-13 on all three arrays
-------------------------------------------------------------
获取DDR型号及频率¶
sudo dmidecode -t memory
# dmidecode 3.1
Getting SMBIOS data from sysfs.
SMBIOS 3.2 present.
# SMBIOS implementations newer than version 3.1.1 are not
# fully supported by this version of dmidecode.
Handle 0x1000, DMI type 16, 23 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: Multi-bit ECC
Maximum Capacity: 7680 GB
Error Information Handle: Not Provided
Number Of Devices: 24
Handle 0x1100, DMI type 17, 84 bytes
Memory Device
Array Handle: 0x1000
Error Information Handle: Not Provided
Total Width: 72 bits
Data Width: 64 bits
Size: 32 GB
Form Factor: DIMM
Set: 1
Locator: A1
Bank Locator: Not Specified
Type: DDR4
Type Detail: Synchronous Registered (Buffered)
Speed: 2666 MT/s
Manufacturer: 00CE00B300CE
Serial Number: 41137A10
Asset Tag: 02184251
Part Number: M393A4K40CB2-CTD
Rank: 2
Configured Clock Speed: 2666 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 1.2 V
Configured Voltage: 1.2 V
DDR规格容量及传输速度对照表
| DDR规格 | 容量 | 传输带宽 |
|---|---|---|
| DDR | 266 | 2.1 GB/s |
| DDR | 333 | 2.6 GB/s |
| DDR | 400 | 3.2 GB/s |
| DDR2 | 533 | 4.2 GB/s |
| DDR2 | 667 | 5.3 GB/s |
| DDR2 | 800 | 6.4 GB/s |
| DDR3 | 1066 | 8.5 GB/s |
| DDR3 | 1333 | 10.6 GB/s |
| DDR3 | 1600 | 12.8 GB/s |
| DDR3 | 1866 | 14.9 GB/s |
| DDR4 | 2133 | 17 GB/s |
| DDR4 | 2400 | 19.2 GB/s |
| DDR4 | 2666 | 21.3 GB/s |
| DDR4 | 3200 | 25.6 GB/s |
计算通道数¶
57 // 21 = 3