鉴于：
BIOS 中禁用超线程的 Broadwell CPU
[root@ny4srv03 ~]# lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Address sizes: 46 bits physical, 48 bits virtual
Byte Order: Little Endian
CPU(s): 44
On-line CPU(s) list: 0-43
Vendor ID: GenuineIntel
BIOS Vendor ID: Intel
Model name: Intel(R) Xeon(R) CPU E5-2696 v4 @ 2.20GHz
BIOS Model name: Intel(R) Xeon(R) CPU E5-2696 v4 @ 2.20GHz
CPU family: 6
Model: 79
Thread(s) per core: 1
Core(s) per socket: 22
Socket(s): 2
Stepping: 1
CPU max MHz: 3700.0000
CPU min MHz: 1200.0000
BogoMIPS: 4399.69
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 cpuid aper
fmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cdp_
l3 invpcid_single intel_ppin tpr_shadow vnmi flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdt_a rdseed adx smap intel_pt xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local d
therm ida arat pln pts
Virtualization features:
Virtualization: VT-x
Caches (sum of all):
L1d: 1.4 MiB (44 instances)
L1i: 1.4 MiB (44 instances)
L2: 11 MiB (44 instances)
L3: 110 MiB (2 instances)
NUMA:
NUMA node(s): 2
NUMA node0 CPU(s): 0-21
NUMA node1 CPU(s): 22-43
Vulnerabilities:
Itlb multihit: KVM: Mitigation: VMX disabled
L1tf: Mitigation; PTE Inversion; VMX vulnerable, SMT disabled
Mds: Vulnerable; SMT disabled
Meltdown: Vulnerable
Mmio stale data: Vulnerable
Retbleed: Not affected
Spec store bypass: Vulnerable
Spectre v1: Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers
Spectre v2: Vulnerable, STIBP: disabled, PBRSB-eIBRS: Not affected
Srbds: Not affected
Tsx async abort: Vulnerable
根据 Intel 64 和 IA-32 架构软件开发人员手册
如果一个处理器内核由两个逻辑处理器共享，则每个逻辑处理器最多可以访问四个计数器 (IA32 PMCO-IA32 PMC3)。这与基于 Nehalem 微架构的上一代处理器相同。
如果处理器内核不被两个逻辑处理器共享，则最多可以看到八个通用计数器。如果 CPUID.OAH:EAX[15:8] 报告 8 个计数器，则 IA32_PMC4-IA32_PMC7 将抄送 MSR 地址 0C5H 到 0C8H。每个计数器都伴随有一个事件选择 MS (IA32_PERFEVTSEL4-IA32_PERFEVTSEL7)。
应有 8 个可访问的性能计数器，并且cpuid确切地表明
[root@ny4srv03 ~]# cpuid -1 | grep counters
number of counters per logical processor = 0x8 (8)
number of contiguous fixed counters = 0x3 (3)
bit width of fixed counters = 0x30 (48)
但是如果我尝试使用perf通过以下方式（在root帐户并与kernel.perf_event_paranoid set to -1）我得到一些奇怪的结果
[root@ny4srv03 ~]# perf stat \
-r 100 \
-e cycles:u \
-e instructions:u \
-e branches:u \
-e branch-misses:u \
-e cache-references:u \
-e cache-misses:u \
-e faults:u \
ls>/dev/null
Performance counter stats for 'ls' (100 runs):
0 cycles:u
668753 instructions:u ( +- 0.01% )
131991 branches:u ( +- 0.00% )
6936 branch-misses:u # 5.25% of all branches ( +- 0.33% )
11105 cache-references:u ( +- 0.13% )
6 cache-misses:u # 0.055 % of all cache refs ( +- 5.86% )
103 faults:u ( +- 0.19% )
0.00100211 +- 0.00000487 seconds time elapsed ( +- 0.49% )
总是显示cycles:u等于0无论我跑多少次perf（请注意-r 100参数），直到我删除其中之一branches:u, branch-misses:u, cache-references:u, cache-misses:u事件。在这种情况下perf按预期工作
[root@ny4srv03 ~]# perf stat \
-r 100 \
-e cycles:u \
-e instructions:u \
-e branches:u \
-e branch-misses:u \
-e cache-references:u \
-e faults:u \
ls>/dev/null
Performance counter stats for 'ls' (100 runs):
614142 cycles:u ( +- 0.06% )
668790 instructions:u # 1.09 insn per cycle ( +- 0.00% )
132052 branches:u ( +- 0.00% )
6874 branch-misses:u # 5.21% of all branches ( +- 0.11% )
10735 cache-references:u ( +- 0.05% )
101 faults:u ( +- 0.06% )
0.00095650 +- 0.00000108 seconds time elapsed ( +- 0.11% )
perf在这些情况下也能按预期工作
- 如果获取指标
cycles事件要么根本没有修饰符，要么带有:k修饰语
[root@ny4srv03 ~]# perf stat \
-r 100 \
-e cycles \
-e instructions:u \
-e branches:u \
-e branch-misses:u \
-e cache-references:u \
-e cache-misses:u \
-e faults:u \
ls>/dev/null
Performance counter stats for 'ls' (100 runs):
1841276 cycles ( +- 0.79% )
668400 instructions:u ( +- 0.00% )
131966 branches:u ( +- 0.00% )
6121 branch-misses:u # 4.64% of all branches ( +- 0.40% )
10987 cache-references:u ( +- 0.16% )
0 cache-misses:u # 0.000 % of all cache refs
102 faults:u ( +- 0.18% )
0.00102359 +- 0.00000649 seconds time elapsed ( +- 0.63% )
- 如果超线程在 BIOS 中启用并通过以下命令禁用
nosmt内核参数
[root@ny4srv03 ~]# perf stat \
-r 100 \
-e cycles:u \
-e instructions:u \
-e branches:u \
-e branch-misses:u \
-e cache-references:u \
-e cache-misses:u \
-e faults:u \
ls>/dev/null
Performance counter stats for 'ls' (100 runs):
618443 cycles:u ( +- 0.39% )
668466 instructions:u # 1.05 insn per cycle ( +- 0.00% )
131968 branches:u ( +- 0.00% )
6529 branch-misses:u # 4.95% of all branches ( +- 0.34% )
11096 cache-references:u ( +- 0.47% )
1 cache-misses:u # 0.010 % of all cache refs ( +- 53.16% )
107 faults:u ( +- 0.18% )
0.00097825 +- 0.00000554 seconds time elapsed ( +- 0.57% )
在这种情况下cpuid还显示只有 4 个可用的性能计数器
[root@ny4srv03 ~]# cpuid -1 | grep counters
number of counters per logical processor = 0x4 (4)
number of contiguous fixed counters = 0x3 (3)
bit width of fixed counters = 0x30 (48)
所以我想知道是否有错误perf或某种系统配置错误。能否请你帮忙？
Update 1
尝试跑步perf -d表明有NMI watchdog enabled
[root@ny4srv03 likwid]# perf stat \
-e cycles:u \
-e instructions:u \
-e branches:u \
-e branch-misses:u \
-e cache-references:u \
-e cache-misses:u \
-e faults:u \
-d \
ls>/dev/null
Performance counter stats for 'ls':
0 cycles:u
709098 instructions:u
140131 branches:u
6826 branch-misses:u # 4.87% of all branches
11287 cache-references:u
0 cache-misses:u # 0.000 % of all cache refs
104 faults:u
593753 L1-dcache-loads
32677 L1-dcache-load-misses # 5.50% of all L1-dcache accesses
8679 LLC-loads
<not counted> LLC-load-misses (0.00%)
0.001102213 seconds time elapsed
0.000000000 seconds user
0.001134000 seconds sys
Some events weren't counted. Try disabling the NMI watchdog:
echo 0 > /proc/sys/kernel/nmi_watchdog
perf stat ...
echo 1 > /proc/sys/kernel/nmi_watchdog
禁用它有助于获得预期结果
echo 0 > /proc/sys/kernel/nmi_watchdog
[root@ny4srv03 likwid]# perf stat \
-e cycles:u \
-e instructions:u \
-e branches:u \
-e branch-misses:u \
-e cache-references:u \
-e cache-misses:u \
-e faults:u \
-d \
ls>/dev/null
Performance counter stats for 'ls':
745760 cycles:u
708833 instructions:u # 0.95 insn per cycle
140122 branches:u
6757 branch-misses:u # 4.82% of all branches
11503 cache-references:u
0 cache-misses:u # 0.000 % of all cache refs
101 faults:u
586223 L1-dcache-loads
32856 L1-dcache-load-misses # 5.60% of all L1-dcache accesses
8794 LLC-loads
29 LLC-load-misses # 0.33% of all LL-cache accesses
0.001000925 seconds time elapsed
0.000000000 seconds user
0.001080000 seconds sys
但还是没有解释为什么cycles:u is 0 with nmi_watchdog即使启用dmesg shows
[ 0.300779] NMI watchdog: Enabled. Permanently consumes one hw-PMU counter.
Update 2
I found 这个好评论在来源中类似的工具套件表明
请注意，Intel Broadwell 上的计数器 PMC4-7 已损坏。他们
如果应用用户级或内核级过滤，则不要增加。用户级
LIKWID 中默认过滤，因此添加了内核级过滤
PMC4-7 自动。返回的计数可能要高得多。
所以它可以解释这种行为，所以现在找到这个信息的来源很有趣 if os.
