為什麼我的 CPU 永遠不會超過 60-70% 的 CPU 使用率？瓶頸在哪裡？

April 29, 2018

在我的 CPU 圖表中，我最近注意到，在編譯東西時，我似乎永遠無法達到 100% 的使用率，它只會在最大 60-70% 左右上下波動。

例子：

相比之下，當在我的工作電腦上完成時，此圖是完全不透明的。

我想深入了解這一點，並使用壓力實用程序來模擬 CPU 使用情況，並使用 vmstat 進行觀察。我正在執行 CPU 核心數從 1 到 15 的壓力（我的 CPU 有 12 個邏輯核心）。結果如下，第 1 行對應 1 個核心執行 100%，第 2 行是 2 個核心，依此類推：

procs -----------------------memory---------------------- ---swap-- -----io---- -system-- --------cpu--------
r  b         swpd         free         buff        cache   si   so    bi    bo   in   cs  us  sy  id  wa  st
1  0            0     24455180       465548      2862716    0    0     0    38  944 3184  11   1  88   0   0
3  0            0     24508640       465552      2862684    0    0     0   196 1112 2841  18   1  81   0   0
3  0            0     24556876       465564      2865096    0    0     0    63 1880 4569  30   1  70   0   0
4  0            0     24624764       465576      2865044    0    0     0    11 1414 1005  34   0  66   0   0
5  0            0     24625228       465580      2865068    0    0     0     9 1603 1029  42   0  58   0   0
6  0            0     24763772       465600      2864912    0    0     1   159 1973 1032  51   0  49   0   0
8  0            0     24786696       465600      2864844    0    0     0     9 2460  751  56   0  44   0   0
8  0            0     24805572       465600      2864864    0    0     0    78 2619  808  61   0  38   0   0
10  0            0     24811064       465604      2864852    0    0     0    50 2532  761  56   0  44   0   0
14  0            0     24809904       465616      2865180    0    0     0     4 2823 1049  63   0  37   0   0
13  0            0     24868936       465620      2865116    0    0     0    76 2596  709  57   0  43   0   0
19  0            0     24910408       465628      2866136    0    0     0    12 2526  738  56   0  44   0   0
16  0            0     24914768       465636      2865244    0    0     0    36 2757  720  62   0  38   0   0
18  0            0     24914332       465644      2865256    0    0     0     3 2629  862  59   0  41   0   0
19  0            0     24945952       465648      2866224    0    0     0    33 2642  678  59   0  41   0   0

我執行的腳本：

for corecount in $(seq 15); do
   stress -c $corecount &gt;/dev/null&
   sleep 1
   vmstat -w 4 2 | tail -1
   pkill stress
   sleep 1
done

通過查看該us列，我發現 CPU 使用率按預期線性增加，最多可達 6-8 個邏輯核心，但之後它又遇到了其他瓶頸。滑鼠游標此時開始滯後，如果我在影片播放器執行時嘗試執行，它也會在此時開始卡頓。（為了比較，這是在我的工作電腦上完成的完全相同的測試：http: //pastebin.com/MHPSR4E0。這裡的 cpu 使用率只是線性上升到 99/100 並保持在那裡（飽和度在第 8 行，因為這是一個8核CPU））

（這是整個測試執行的 cpu 圖，阻塞點可見：）

一般資訊：

Ubuntu 16.04 LTS，32 GB 記憶體，i7-5820K 6 核 CPU。

免費-h

             total        used        free      shared  buff/cache   available
Mem:            31G        4,8G         23G         90M        3,3G         26G
Swap:           15G          0B         15G

/proc/cpuinfo

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 63
model name      : Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz
stepping        : 2
microcode       : 0x2d
cpu MHz         : 1236.339
cache size      : 15360 KB
physical id     : 0
siblings        : 12
core id         : 0
cpu cores       : 6
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 15
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 pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm ida arat pln pts dtherm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm xsaveopt cqm_llc cqm_occup_llc
bugs            :
bogomips        : 6599.39
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

[...]

processor       : 11
vendor_id       : GenuineIntel
cpu family      : 6
model           : 63
model name      : Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz
stepping        : 2
microcode       : 0x2d
cpu MHz         : 1200.246
cache size      : 15360 KB
physical id     : 0
siblings        : 12
core id         : 5
cpu cores       : 6
apicid          : 11
initial apicid  : 11
fpu             : yes
fpu_exception   : yes
cpuid level     : 15
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 pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm ida arat pln pts dtherm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm xsaveopt cqm_llc cqm_occup_llc
bugs            :
bogomips        : 6599.39
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

lspci

00:00.0 Host bridge: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DMI2 (rev 02)
00:01.0 PCI bridge: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCI Express Root Port 1 (rev 02)
00:01.1 PCI bridge: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCI Express Root Port 1 (rev 02)
00:02.0 PCI bridge: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCI Express Root Port 2 (rev 02)
00:02.2 PCI bridge: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCI Express Root Port 2 (rev 02)
00:02.3 PCI bridge: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCI Express Root Port 2 (rev 02)
00:03.0 PCI bridge: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCI Express Root Port 3 (rev 02)
00:05.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Address Map, VTd_Misc, System Management (rev 02)
00:05.1 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Hot Plug (rev 02)
00:05.2 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 RAS, Control Status and Global Errors (rev 02)
00:05.4 PIC: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 I/O APIC (rev 02)
00:11.0 Unassigned class [ff00]: Intel Corporation C610/X99 series chipset SPSR (rev 05)
00:14.0 USB controller: Intel Corporation C610/X99 series chipset USB xHCI Host Controller (rev 05)
00:16.0 Communication controller: Intel Corporation C610/X99 series chipset MEI Controller #1 (rev 05)
00:19.0 Ethernet controller: Intel Corporation Ethernet Connection (2) I218-V (rev 05)
00:1a.0 USB controller: Intel Corporation C610/X99 series chipset USB Enhanced Host Controller #2 (rev 05)
00:1b.0 Audio device: Intel Corporation C610/X99 series chipset HD Audio Controller (rev 05)
00:1c.0 PCI bridge: Intel Corporation C610/X99 series chipset PCI Express Root Port #1 (rev d5)
00:1c.4 PCI bridge: Intel Corporation C610/X99 series chipset PCI Express Root Port #5 (rev d5)
00:1d.0 USB controller: Intel Corporation C610/X99 series chipset USB Enhanced Host Controller #1 (rev 05)
00:1f.0 ISA bridge: Intel Corporation C610/X99 series chipset LPC Controller (rev 05)
00:1f.2 SATA controller: Intel Corporation C610/X99 series chipset 6-Port SATA Controller [AHCI mode] (rev 05)
00:1f.3 SMBus: Intel Corporation C610/X99 series chipset SMBus Controller (rev 05)
06:00.0 VGA compatible controller: NVIDIA Corporation GF104 [GeForce GTX 460] (rev a1)
06:00.1 Audio device: NVIDIA Corporation GF104 High Definition Audio Controller (rev a1)
08:00.0 USB controller: ASMedia Technology Inc. ASM1142 USB 3.1 Host Controller
ff:0b.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 R3 QPI Link 0 & 1 Monitoring (rev 02)
ff:0b.1 Performance counters: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 R3 QPI Link 0 & 1 Monitoring (rev 02)
ff:0b.2 Performance counters: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 R3 QPI Link 0 & 1 Monitoring (rev 02)
ff:0c.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Unicast Registers (rev 02)
ff:0c.1 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Unicast Registers (rev 02)
ff:0c.2 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Unicast Registers (rev 02)
ff:0c.3 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Unicast Registers (rev 02)
ff:0c.4 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Unicast Registers (rev 02)
ff:0c.5 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Unicast Registers (rev 02)
ff:0f.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Buffered Ring Agent (rev 02)
ff:0f.1 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Buffered Ring Agent (rev 02)
ff:0f.4 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 System Address Decoder & Broadcast Registers (rev 02)
ff:0f.5 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 System Address Decoder & Broadcast Registers (rev 02)
ff:0f.6 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 System Address Decoder & Broadcast Registers (rev 02)
ff:10.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCIe Ring Interface (rev 02)
ff:10.1 Performance counters: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 PCIe Ring Interface (rev 02)
ff:10.5 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Scratchpad & Semaphore Registers (rev 02)
ff:10.6 Performance counters: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Scratchpad & Semaphore Registers (rev 02)
ff:10.7 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Scratchpad & Semaphore Registers (rev 02)
ff:12.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Home Agent 0 (rev 02)
ff:12.1 Performance counters: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Home Agent 0 (rev 02)
ff:13.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Target Address, Thermal & RAS Registers (rev 02)
ff:13.1 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Target Address, Thermal & RAS Registers (rev 02)
ff:13.2 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel Target Address Decoder (rev 02)
ff:13.3 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel Target Address Decoder (rev 02)
ff:13.4 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel Target Address Decoder (rev 02)
ff:13.5 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel Target Address Decoder (rev 02)
ff:13.6 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO Channel 0/1 Broadcast (rev 02)
ff:13.7 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO Global Broadcast (rev 02)
ff:14.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 0 Thermal Control (rev 02)
ff:14.1 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 1 Thermal Control (rev 02)
ff:14.2 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 0 ERROR Registers (rev 02)
ff:14.3 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 1 ERROR Registers (rev 02)
ff:14.6 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO (VMSE) 0 & 1 (rev 02)
ff:14.7 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO (VMSE) 0 & 1 (rev 02)
ff:15.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 2 Thermal Control (rev 02)
ff:15.1 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 3 Thermal Control (rev 02)
ff:15.2 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 2 ERROR Registers (rev 02)
ff:15.3 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 0 Channel 3 ERROR Registers (rev 02)
ff:16.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 1 Target Address, Thermal & RAS Registers (rev 02)
ff:16.6 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO Channel 2/3 Broadcast (rev 02)
ff:16.7 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO Global Broadcast (rev 02)
ff:17.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Integrated Memory Controller 1 Channel 0 Thermal Control (rev 02)
ff:17.4 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO (VMSE) 2 & 3 (rev 02)
ff:17.5 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO (VMSE) 2 & 3 (rev 02)
ff:17.6 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO (VMSE) 2 & 3 (rev 02)
ff:17.7 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 DDRIO (VMSE) 2 & 3 (rev 02)
ff:1e.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Power Control Unit (rev 02)
ff:1e.1 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Power Control Unit (rev 02)
ff:1e.2 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Power Control Unit (rev 02)
ff:1e.3 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Power Control Unit (rev 02)
ff:1e.4 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 Power Control Unit (rev 02)
ff:1f.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 VCU (rev 02)
ff:1f.2 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 VCU (rev 02)

/proc/meminfo

MemTotal:       32841924 kB
MemFree:        24244428 kB
MemAvailable:   27418672 kB
Buffers:          478012 kB
Cached:          2622028 kB
SwapCached:            0 kB
Active:          6606180 kB
Inactive:        1240728 kB
Active(anon):    4758584 kB
Inactive(anon):    85340 kB
Active(file):    1847596 kB
Inactive(file):  1155388 kB
Unevictable:        8020 kB
Mlocked:            8020 kB
SwapTotal:      16669692 kB
SwapFree:       16669692 kB
Dirty:               284 kB
Writeback:             0 kB
AnonPages:       4754864 kB
Mapped:           780304 kB
Shmem:             93528 kB
Slab:             346300 kB
SReclaimable:     257036 kB
SUnreclaim:        89264 kB
KernelStack:       22112 kB
PageTables:       109808 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    33090652 kB
Committed_AS:   16302224 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      371016 kB
VmallocChunk:   34358945788 kB
HardwareCorrupted:     0 kB
AnonHugePages:    761856 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:      537784 kB
DirectMap2M:     5648384 kB
DirectMap1G:    29360128 kB

使用 10 個核心進行壓力測試時，來自 ksysguard 的更詳細的 cpu 使用螢幕截圖：

**到底是怎麼回事？**我可以觀察核心的哪些其他部分以了解發生了什麼？是否有一些 cpu 調度程序配置一直是這樣的，我絕對確定我以前能夠以 100% 的 cpu 使用率進行編譯，沒有滑鼠延遲，除了風扇執行之外沒有真正注意到它。

要在 Linux 上調試調度或應用程序性能問題，最好在perf stat. 它報告有關處理器管道、其停滯週期或記憶體行為的統計資訊。
可能出現的問題：
Linux/調度程序錯誤
英特爾 HT 跟不上您的執行緒
記憶體無法為程序提供足夠的數據
為了複雜性，解析度是錯誤的/舊核心（4.2.0），而不是 Ubuntu 16.04 的預期 4.4.0。更新解決了問題。

我認為這不是問題，而是您正在執行的程序的行為。
您的應用程序（編譯）沒有使用 100% 的 CPU，它可能會使用相當多的 IO。當應用程序進行 IO 時，它會進入 iowait 模式。在完成 IO 操作之前，它不能使用 CPU。
注意中的“等待時間” top。

引用自：https://unix.stackexchange.com/questions/280439

為什麼我的 CPU 永遠不會超過 60-70% 的 CPU 使用率？瓶頸在哪裡？

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