为什么 cpu-cycles 远小于 cpu 当前频率? [英] why is cpu-cycles much less than cpu current frequency?
问题描述
我的 cpu 最大频率是 2.8GHZ，cpu 频率模式是性能，但是 cpu-cycles 从性能上只有 0.105GHZ，为什么??
cpu-cycles 事件是 0x3c，它是 CPU_CLK_UNHALTED.THREAD_P 还是 CPU_CLK_THREAD_UNHALTED.REF_XCLK?
我可以直接从 perf 读取 PMC 寄存器吗?
现在通过命令'mpstat'，cpu-8的使用率达到了90%.
CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle8 0.00 0.00 0.98 0.00 0.00 0.00 0.00 89.22 0.00 9.808 0.00 0.00 0.99 0.00 0.00 0.00 0.00 88.12 0.00 10.89CPU 为 Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz.
处理器:8vendor_id : 正版英特尔CPU系列:6型号 : 62型号名称 : Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz步数:4微码:0x428CPU 兆赫:2800.000缓存大小:25600 KB我想通过 perf 了解一下 cpu-8.
perf stat -C 8CPU(s) 8"的性能计数器统计信息:8828.237941 任务时钟(毫秒)# 1.000 个 CPU11,550 次上下文切换 # 0.001 M/sec0 cpu-migrations # 0.000 K/秒0 页错误 # 0.000 K/秒926,167,840 个周期 # 0.105 GHz4,012,135,689 停顿周期前端 # 433.20% 前端周期空闲473,099,833 条指令 # 每个周期 0.51 insn# 每个insn 8.48 个停滞周期98,346,040 个分支 # 11.140 M/秒1,254,592 次分支未命中 # 占所有分支的 1.28%8.828177754 秒时间过去cpu-cycles只有0.105GHZ，真的很奇怪.
我试图理解 cpu-cycles 的含义.
cat/sys/bus/event_source/devices/cpu/events/cpu-cycles事件=0x3c我查找文档英特尔® 64 位和 IA-32 架构软件开发人员手册第 3 卷"，第 19.6 节第 40 页.
我还检查了 cpu 频率设置，cpu 应该以最大频率运行.
cat scaling_governor表现猫缩放_governor表现================================================/p>
我试试这个命令:
taskset -c 8 压力 --cpu 1性能统计 -C 8 睡眠 10CPU(s) 8"的性能计数器统计信息:10000.633899 任务时钟(毫秒)# 1.000 个 CPU 使用1,823 次上下文切换 # 0.182 K/秒0 cpu-migrations # 0.000 K/秒8 个页面错误 # 0.001 K/sec29,792,267,638 个周期 # 2.979 GHz5,866,181,553 停顿周期前端 # 19.69% 前端周期空闲54,171,961,339 条指令 # 每个周期 1.82 insn# 每个insn 0.11 个停滞周期16,356,002,578 个分支 # 1635.497 M/秒33,041,249 次分支未命中 # 占所有分支的 0.20%10.000592203 秒时间过去了<小时>
关于我的环境的一些详细信息
我运行一个应用程序，我们称它为A"，在虚拟机V"中，在主机H"中.
虚拟机由qume-kvm创建.
应用程序用于从网络接收数据包并进行处理.
cpu-cycles 可能因 CPU 进入 C1 或 C2 空闲状态而被冻结.
My cpu max frequency is 2.8GHZ and cpu frequency mode is performance, but cpu-cycles is only 0.105GHZ from perf, why??
The cpu-cycles event is 0x3c, it is CPU_CLK_UNHALTED.THREAD_P or CPU_CLK_THREAD_UNHALTED.REF_XCLK ?
Could I read the PMC register from perf directly?
Now the usage of cpu-8 reaches 90% by the command 'mpstat'.
CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
8 0.00 0.00 0.98 0.00 0.00 0.00 0.00 89.22 0.00 9.80
8 0.00 0.00 0.99 0.00 0.00 0.00 0.00 88.12 0.00 10.89
The cpu is Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz.
processor : 8
vendor_id : GenuineIntel
cpu family : 6
model : 62
model name : Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz
stepping : 4
microcode : 0x428
cpu MHz : 2800.000
cache size : 25600 KB
I want to get some idea about the cpu-8 by perf.
perf stat -C 8
Performance counter stats for 'CPU(s) 8':
8828.237941 task-clock (msec) # 1.000 CPUs utilized
11,550 context-switches # 0.001 M/sec
0 cpu-migrations # 0.000 K/sec
0 page-faults # 0.000 K/sec
926,167,840 cycles # 0.105 GHz
4,012,135,689 stalled-cycles-frontend # 433.20% frontend cycles idle
473,099,833 instructions # 0.51 insn per cycle
# 8.48 stalled cycles per insn
98,346,040 branches # 11.140 M/sec
1,254,592 branch-misses # 1.28% of all branches
8.828177754 seconds time elapsed
The cpu-cycles is only 0.105GHZ,it is really strange.
I try to understand the cpu-cycles meaning.
cat /sys/bus/event_source/devices/cpu/events/cpu-cycles
event=0x3c
I look up the document "Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3", at 19.6 session, page 40.
I also check the cpu frequency setting, the cpu should be running at the max frequency.
cat scaling_governor
performance
cat scaling_governor
performance
==============================================
I try this command:
taskset -c 8 stress --cpu 1
perf stat -C 8 sleep 10
Performance counter stats for 'CPU(s) 8':
10000.633899 task-clock (msec) # 1.000 CPUs utilized
1,823 context-switches # 0.182 K/sec
0 cpu-migrations # 0.000 K/sec
8 page-faults # 0.001 K/sec
29,792,267,638 cycles # 2.979 GHz
5,866,181,553 stalled-cycles-frontend # 19.69% frontend cycles idle
54,171,961,339 instructions # 1.82 insn per cycle
# 0.11 stalled cycles per insn
16,356,002,578 branches # 1635.497 M/sec
33,041,249 branch-misses # 0.20% of all branches
10.000592203 seconds time elapsed
some detail information about my environment
I run a application, let's call it 'A', in a virtual machine 'V', in a host 'H'。
The virtual machine is created by qume-kvm.
The application is used to receive packets from network and deal with them.
cpu-cycles could be frozen due to that CPU enters C1 or C2 idle state.
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