1kvmexit(8) System Manager's Manual kvmexit(8)
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6 kvmexit - Display the exit_reason and its statistics of each vm exit.
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9 kvmexit [-h] [-p PID [-v VCPU | -a] ] [-t TID | -T 'TID1,TID2'] [dura‐
10 tion]
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13 Considering virtual machines' frequent exits can cause performance
14 problems, this tool aims to locate the frequent exited reasons and then
15 find solutions to reduce or even avoid the exit, by displaying the de‐
16 tail exit reasons and the counts of each vm exit for all vms running on
17 one physical machine.
18 This tool uses a PERCPU_ARRAY: pcpuArrayA and a percpu_hash: hashA to
20 collaboratively store each kvm exit reason and its count. The reason is
21 there exists a rule when one vcpu exits and re-enters, it tends to con‐
22 tinue to run on the same physical cpu as the last cycle, which is also
23 called 'cache hit'. Thus we turn to use a PERCPU_ARRAY to record the
24 'cache hit' situation to speed things up; and for other cases, then use
25 a percpu_hash.
26 As RAW_TRACEPOINT_PROBE(kvm_exit) consumes less cpu cycles, when this
28 tool is used, it firstly tries to employ raw tracepoints in modules,
29 and if failes, then fall back to regular tracepoint.
30 Limitation: In view of the hardware-assisted virtualization technology
32 of different architectures, currently we only adapt on vmx in intel.
33 Since this uses BPF, only the root user can use this tool.
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37 CONFIG_BPF and bcc.
38 This also requires Linux 4.7+ (BPF_PROG_TYPE_TRACEPOINT support).
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42 -h Print usage message.
43 -p PID Display process with this PID only, collpase all tids with exit
45 reasons sorted in descending order.
46 -v VCPU
48 Display this VCPU only for this PID.
49 -a ALLTIDS
51 Display all TIDS for this PID.
52 -t TID Display thread with this TID only with exit reasons sorted in
54 descending order.
55 -T 'TID1,TID2'
57 Display threads for a union like {395490, 395491}.
58 duration
60 Duration of display, after sleeping several seconds.
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63 Display kvm exit reasons and statistics for all threads... Hit Ctrl-C
64 to end:
65 # kvmexit
66 Display kvm exit reasons and statistics for all threads after sleeping
68 6 secs:
69 # kvmexit 6
70 Display kvm exit reasons and statistics for PID 1273795 after sleeping
72 5 secs:
73 # kvmexit -p 1273795 5
74 Display kvm exit reasons and statistics for PID 1273795 and its all
76 threads after sleeping 5 secs:
77 # kvmexit -p 1273795 5 -a
78 Display kvm exit reasons and statistics for PID 1273795 VCPU 0... Hit
80 Ctrl-C to end:
81 # kvmexit -p 1273795 -v 0
82 Display kvm exit reasons and statistics for PID 1273795 VCPU 0 after
84 sleeping 4 secs:
85 # kvmexit -p 1273795 -v 0 4
86 Display kvm exit reasons and statistics for TID 1273819 after sleeping
88 10 secs:
89 # kvmexit -t 1273819 10
90 Display kvm exit reasons and statistics for TIDS ['1273820',
92 '1273819']... Hit Ctrl-C to end:
93 # kvmexit -T '1273820,1273819'
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96 This traces the "kvm_exit" kernel function, records the exit reason and
97 calculates its counts. Contrast with filling more vm-exit reason debug
98 entries, this tool is more easily and flexibly: the bcc python logic
99 could provide nice kernel aggregation and custom output, the bpf in-
100 kernel percpu_array and percpu_cache further improves performance.
101 The impact of using this tool on the host should be negligible. While
103 this tool is very efficient, it does affect the guest virtual machine
104 itself, the average test results on guest vm are as follows:
105 | cpu cycles
106 no TP | 1127
107 regular TP | 1277 (13% downgrade)
108 RAW TP | 1187 (5% downgrade)
109 Host: echo 1 > /proc/sys/net/core/bpf_jit_enable
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113 This is from bcc.
114 https://github.com/iovisor/bcc
116 Also look in the bcc distribution for a companion _examples.txt file
118 containing example usage, output, and commentary for this tool.
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121 Linux
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124 Unstable - in development.
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127 Fei Li <lifei.shirley@bytedance.com>
128USER COMMANDS 2021-07-08 kvmexit(8)