评估内存性能
使用工具： stream
官方指导： 教程
stream是内存性能评估的工业标准之一，工具现由弗吉尼亚计算机系维护。
下载源码
这里以C源码为例。
wget https://www.cs.virginia.edu/stream/FTP/Code/stream.c
完整的项目代码，请访问 链接
编译
gcc -O stream.c -o stream
执行
./stream
执行结果
me@ubuntu:~/stream$ ./stream
-------------------------------------------------------------
STREAM version $Revision: 5.10 $
-------------------------------------------------------------
This system uses 8 bytes per array element.
-------------------------------------------------------------
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.
-------------------------------------------------------------
Your clock granularity/precision appears to be 1 microseconds.
Each test below will take on the order of 17729 microseconds.
(= 17729 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: 10266.2 0.015629 0.015585 0.015700
Scale: 10588.2 0.015190 0.015111 0.015333
Add: 11421.5 0.021111 0.021013 0.021220
Triad: 11416.0 0.021077 0.021023 0.021138
-------------------------------------------------------------
Solution Validates: avg error less than 1.000000e-13 on all three arrays
-------------------------------------------------------------
me@ubuntu:~/stream$
内存大小
获取设备内存硬件信息：最大支持512GB，最大支持16个内存
me@ubuntu:~/stream$ sudo dmidecode -t memory
[sudo] password for me:
# dmidecode 3.1
Getting SMBIOS data from sysfs.
SMBIOS 3.0.0 present.
Handle 0x0007, DMI type 16, 23 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: None
Maximum Capacity: 512 GB
Error Information Handle: Not Provided
Number Of Devices: 16
1 内存条 0x0009
Handle 0x0009, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0007
Error Information Handle: Not Provided
Total Width: 72 bits
Data Width: 64 bits
Size: 32 GB
Form Factor: DIMM
Set: None
Locator: DIMM000 J11
Bank Locator: SOCKET 0 CHANNEL 0 DIMM 0
Type: DDR4
Type Detail: Synchronous Registered (Buffered)
Speed: 2400 MT/s
Manufacturer: Samsung
Serial Number: 0x351254BC
Asset Tag: 1709
Part Number: M393A4K40BB1-CRC
Rank: 2
Configured Clock Speed: 2400 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 2.0 V
Configured Voltage: 1.2 V
2 内存条 0x000D
Handle 0x000D, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0007
Error Information Handle: Not Provided
Total Width: 72 bits
Data Width: 64 bits
Size: 32 GB
Form Factor: DIMM
Set: None
Locator: DIMM020 J5
Bank Locator: SOCKET 0 CHANNEL 2 DIMM 0
Type: DDR4
Type Detail: Synchronous Registered (Buffered)
Speed: 2400 MT/s
Manufacturer: Samsung
Serial Number: 0x35125985
Asset Tag: 1709
Part Number: M393A4K40BB1-CRC
Rank: 2
Configured Clock Speed: 2400 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 2.0 V
Configured Voltage: 1.2 V
3 内存条 0x0011
Handle 0x0011, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0007
Error Information Handle: Not Provided
Total Width: 72 bits
Data Width: 64 bits
Size: 32 GB
Form Factor: DIMM
Set: None
Locator: DIMM100 J23
Bank Locator: SOCKET 1 CHANNEL 0 DIMM 0
Type: DDR4
Type Detail: Synchronous Registered (Buffered)
Speed: 2400 MT/s
Manufacturer: Samsung
Serial Number: 0x351258E0
Asset Tag: 1709
Part Number: M393A4K40BB1-CRC
Rank: 2
Configured Clock Speed: 2400 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 2.0 V
Configured Voltage: 1.2 V
4 内存条 0x0015
Handle 0x0015, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0007
Error Information Handle: Not Provided
Total Width: 72 bits
Data Width: 64 bits
Size: 32 GB
Form Factor: DIMM
Set: None
Locator: DIMM120 J17
Bank Locator: SOCKET 1 CHANNEL 2 DIMM 0
Type: DDR4
Type Detail: Synchronous Registered (Buffered)
Speed: 2400 MT/s
Manufacturer: Samsung
Serial Number: 0x35125924
Asset Tag: 1709
Part Number: M393A4K40BB1-CRC
Rank: 2
Configured Clock Speed: 2400 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 2.0 V
Configured Voltage: 1.2 V
一共4个内存条， 每一个都是32GB，2400MT/s, DDR4。所以可用内存是4*32=128GB,用命令看到的结果是128655MB。
me@ubuntu:~/stream$ free -m
total used free shared buff/cache available
Mem: 128665 31887 2905 3 93873 95806
Swap: 2047 91 1956
me@ubuntu:~/stream$ free -mh
total used free shared buff/cache available
Mem: 125G 31G 2.8G 3.1M 91G 93G
Swap: 2.0G 91M 1.9G
me@ubuntu:~/syslog$ free -b
total used free shared buff/cache available
Mem: 134915833856 33471602688 617598976 3317760 100826632192 100424712192
Swap: 2147479552 96468992 2051010560
物理内存
128G =128*2^30 B = 137438953472
free 命令可以看到的，应用程序可使用内存为
125G = 134915833856 B,
两者相差
137438953472 - 134915833856 = 2523119616 B = 2.34 GB
相差内存查阅资料提示：bios会占用一部分， 内核会预留一部分，需要进一步分析
内存速率
4个内存条，都标识2400MT/s。 MT/s指的是MegaTransfers per second ，每秒万兆次传输。和时钟频率单位是两码事， 因为一个时钟周期内可能发生两次传输。
内存条的数据位宽是64bit，所以每个内存条的理论带宽是：
2400M * 64bit = 153600 Mbit/s = 19200 MB/s = 18.75 GB/s
stream测出的内存带宽是11416.0 MB/s，是应用程序获得的可持续带宽, 和单条内存的理论贷款还是有差距，并且内存条可以组成多通道，应该可获得的带宽要大于单条内存的带宽