different CPU cache size reported by /sys/device/ and dmidecode
caching, linux
Solution
A few things:
- You have a quad-core CPU
- The `index<n>` name in `/sys/devices/system/cpu/cpu<n>/cache` does not correspond to L1/L2/L3 etc. There is a `.../index<n>/level` file that will tell you the level of the cache.
- Your L1 cache is split into two caches (likely `index0` and `index1`), one for data, and one for instructions (see `.../index<n>/type`), per core. 4 cores * 2 halves * 32K matches the 256K that `dmidecode` reports.
- The L2 cache is split per-core. 4 cores * 256K (from `index2`) = 1024K, which matches `dmidecode`s L2 number.
Problem
I'm trying to get the size of different cache level in my system. I tried two techniques. a) Using information from /sys/device. Here is the output. ``` $ cat /sys/devices/system/cpu/cpu0/cache/index1/size 32K $ cat /sys/devices/system/cpu/cpu0/cache/index2/size 256K $ cat /sys/devices/system/cpu/cpu0/cache/index3/size 8192K ``` b) Using information from dmidecode ``` $ sudo dmidecode -t cache Cache Information Socket Designation: CPU Internal L1 Configuration: Enabled, Not Socketed, Level 1 Operational Mode: Write Through Location: Internal Installed Size: 256 KB Maximum Size: 256 KB < .... > Cache Information Socket Designation: CPU Internal L2 Configuration: Enabled, Not Socketed, Level 2 Operational Mode: Write Through Location: Internal Installed Size: 1024 KB Maximum Size: 1024 KB < .... > Cache Information Socket Designation: CPU Internal L3 Configuration: Enabled, Not Socketed, Level 3 Operational Mode: Write Back Location: Internal Installed Size: 8192 KB Maximum Size: 8192 KB < .... > ``` The size reported for L2 and L3 cache is different. Any ideas as to a) why this discrepancy? b) Which method gives the correct value? Other related information: ``` $uname -a Linux 3.0.0-14-generic #23somerville3-Ubuntu SMP Mon Dec 12 09:20:18 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 58 model name : Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz stepping : 9 cpu MHz : 2400.000 cache size : 8192 KB physical id : 0 siblings : 8 core id : 0 cpu cores : 4 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 x2apic popcnt aes xsave avx f16c rdrand lahf_lm ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid fsgsbase smep erms bogomips : 6784.23 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: < ... > ```