108. memory information¶
108.1. dmidecode¶
dmidecode可以获取内存的完整信息，插槽，最大内存，DRR4，内存频率，电压等。
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
获取设备内存硬件信息：最大支持512GB，最大支持16个内存插槽，当前设备插有4个内存条，每个内存条大小是32GB。
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
108.2. free¶
free可以获取系统可用内存大小、内存占用情况。
root@ubuntu:~# free -h
total used free shared buff/cache available
Mem: 125G 810M 105G 1.1M 19G 123G
Swap: 2.0G 0B 2.0G
root@ubuntu:~# free -m
total used free shared buff/cache available
Mem: 128665 810 108301 1 19554 126911
Swap: 2047 0 2047
root@ubuntu:~# free -b
total used free shared buff/cache available
Mem: 134915833856 849604608 113562103808 1134592 20504125440 133076762624
Swap: 2147479552 0 2147479552
root@ubuntu:~#
看到可用内存是125GB，和4个43GB内存条的128GB总容量存在差距。
108.3. 数据对比¶
计算机中的字节大小换算方式
| GB | MB | KB | B |
|---|---|---|---|
| 进制 | 1024 | 1024 | 1024 |
| 1 | 1024^1 | 1024^2 | 1024^3 |
| 1 | 2^10 | 2^20 | 2^30 |
| 1 | 1024 | 1048576 | 1073741824 |
物理内存大小：
128G =128*2^30 B = 137438953472 B
可用实际大小：free 命令可以看到的，应用程序可使用内存为
134915833856 B ≈ 125G
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
108.4. 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
108.4.1. DDR带宽能力¶
Intel Xeon 6148 1P:
2666MHz * 64bit/s ÷ 8 * 6 * 0.9 ≈ 112.4 GB/s
Kunpeng 920 4826 1P:
2933MHz * 64bit/s ÷ 8 * 8 * 0.9 ≈ 164.9 GB/s
注解
0.9 是DDR控制器效率