perf kvm to profile vm_exit
Optimizing VM_EXITs will significantly improve performance VMs. All the major improvements in VM world is mainly focusing on reducing the number of VM_EXITs. To optimize it, first we should able to measure it. Initially the tool kvm_stat was designed for this purpose, later it has been added inside perf itself.
To profile VM_EXITs while running sysbench,
- Get
pidof the VM task - 127894 - Get the IP of that machine - 192.168.122.194
Make sure you can ssh to that machine without password - Install
sysbenchinside the VM
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$ sudo perf kvm stat record -p 127894 ssh 192.168.122.194 -l test_user "sysbench --test=cpu --cpu-max-prime=20000 run"
sysbench 0.4.12: multi-threaded system evaluation benchmark
Running the test with following options:
Number of threads: 1
Doing CPU performance benchmark
Threads started!
Done.
Maximum prime number checked in CPU test: 20000
Test execution summary:
total time: 22.6607s
total number of events: 10000
total time taken by event execution: 22.6598
per-request statistics:
min: 2.13ms
avg: 2.27ms
max: 12.10ms
approx. 95 percentile: 2.88ms
Threads fairness:
events (avg/stddev): 10000.0000/0.00
execution time (avg/stddev): 22.6598/0.00
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 4.779 MB perf.data.guest (52461 samples) ]
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Perf has recorded the data in perf.data.guest in the current directory. Now to view VM_EXITs,
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$ sudo perf kvm stat report --event=vmexit
Analyze events for all VMs, all VCPUs:
VM-EXIT Samples Samples% Time% Min Time Max Time Avg time
MSR_WRITE 9167 35.40% 0.04% 0.45us 9554.94us 3.00us ( +- 41.94% )
EXTERNAL_INTERRUPT 5877 22.69% 0.02% 0.37us 1175.48us 2.43us ( +- 17.90% )
PREEMPTION_TIMER 5728 22.12% 0.01% 0.51us 21.14us 0.62us ( +- 0.87% )
HLT 2232 8.62% 99.92% 0.56us 1001118.99us 30567.94us ( +- 9.88% )
CPUID 2160 8.34% 0.00% 0.40us 12.82us 0.65us ( +- 1.29% )
PAUSE_INSTRUCTION 390 1.51% 0.00% 0.38us 1490.19us 8.27us ( +- 62.22% )
EPT_MISCONFIG 303 1.17% 0.01% 1.04us 167.13us 13.33us ( +- 8.61% )
EOI_INDUCED 37 0.14% 0.00% 0.62us 3.00us 1.24us ( +- 6.58% )
EXCEPTION_NMI 4 0.02% 0.00% 0.42us 0.56us 0.47us ( +- 6.81% )
Total Samples:25898, Total events handled time:68281638.61us.
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