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05 最快的存储器 - Cache ​

Cache 是什么 ​

  • Cache，中文译为高速缓冲存储器；
  • 一种位于 CPU 内部的高速缓存；
  • 用于存储 CPU 频繁访问的数据和指令；
  • 缓存命中可以有效减少 CPU 访问内存的次数；
  • 通常由多级缓存组成，每级缓存的容量和速度均不同；
  • 一般分为 L1 Cache、L2 Cache、L3 Cache，容量和访问时延逐级增加;

Cache 与资源共享 ​

  • L1 Cache：分为 L1i Cache 和 L1d Cache，每个逻辑核独属;
  • L2 Cache：每个物理核独属，两个逻辑核共享；
  • L3 Cache：NUMA 上的所有物理核共享;

Linux 查看 Cache 容量 ​

bash
➜  ~ lscpu | grep "cache:"
L1d cache:                            128 KiB (4 instances)
L1i cache:                            128 KiB (4 instances)
L2 cache:                             16 MiB (4 instances)
L3 cache:                             16 MiB (1 instance)
➜  ~ lscpu
Architecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          48 bits physical, 48 bits virtual
  Byte Order:             Little Endian
CPU(s):                   4
  On-line CPU(s) list:    0-3
Vendor ID:                AuthenticAMD
  BIOS Vendor ID:         Smdbmds
  Model name:             AMD EPYC 7K62 48-Core Processor
    BIOS Model name:      3.0
    CPU family:           23
    Model:                49
    Thread(s) per core:   1
    Core(s) per socket:   4
    Socket(s):            1
    Stepping:             0
    BogoMIPS:             5190.24
    Flags:                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmo
                          v pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext f
                          xsr_opt pdpe1gb rdtscp lm rep_good nopl cpuid extd_apicid ts
                          c_known_freq pni pclmulqdq ssse3 fma cx16 sse4_1 sse4_2 x2ap
                          ic movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm
                           cmp_legacy cr8_legacy abm sse4a misalignsse 3dnowprefetch o
                          svw topoext ibpb vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed
                           adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 arat
Virtualization features:
  Hypervisor vendor:      KVM
  Virtualization type:    full
Caches (sum of all):
  L1d:                    128 KiB (4 instances)
  L1i:                    128 KiB (4 instances)
  L2:                     16 MiB (4 instances)
  L3:                     16 MiB (1 instance)
NUMA:
  NUMA node(s):           1
  NUMA node0 CPU(s):      0-3
Vulnerabilities:
  Gather data sampling:   Not affected
  Itlb multihit:          Not affected
  L1tf:                   Not affected
  Mds:                    Not affected
  Meltdown:               Not affected
  Mmio stale data:        Not affected
  Reg file data sampling: Not affected
  Retbleed:               Mitigation; untrained return thunk; SMT disabled
  Spec rstack overflow:   Vulnerable: Safe RET, no microcode
  Spec store bypass:      Vulnerable
  Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sani
                          tization
  Spectre v2:             Mitigation; Retpolines; IBPB conditional; STIBP disabled; RS
                          B filling; PBRSB-eIBRS Not affected; BHI Not affected
  Srbds:                  Not affected
  Tsx async abort:        Not affected
bash
➜  ~ cat /sys/devices/system/cpu/cpu0/cache/index0/size
32K
➜  ~ cat /sys/devices/system/cpu/cpu0/cache/index1/size
32K
➜  ~ cat /sys/devices/system/cpu/cpu0/cache/index2/size
4096K
➜  ~ cat /sys/devices/system/cpu/cpu0/cache/index3/size
16384K
➜  ~ cat /sys/devices/system/cpu/cpu0/cache/index*/size
32K
32K
4096K
16384K

存储器的层次结构 ​

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