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25 .\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $
32 .Nd kernel tracing facility
35 .Cd options KTR_ENTRIES=8192
36 .Cd options KTR_VERBOSE=1
38 .Cd options KTR_ETHERNET
39 .Cd options KTR_IF_BGE
41 .Cd options KTR_IF_START
44 .Cd options KTR_KERNENTRY
45 .Cd options KTR_MEMORY
46 .Cd options KTR_POLLING
47 .Cd options KTR_SERIALIZER
48 .Cd options KTR_SPIN_CONTENTION
49 .\".Cd options KTR_TCP
50 .Cd options KTR_TESTLOG
51 .Cd options KTR_TOKENS
52 .\".Cd options KTR_TSLEEP
53 .Cd options KTR_USB_MEMORY
58 facility allows kernel events to be logged while the kernel executes so that
59 they can be examined later when debugging.
60 The only mandatory option to enable
67 option sets the size of the buffer of events.
68 It must be a power of two.
69 The size of the buffer in the currently running kernel can be found via the
71 .Va debug.ktr.entries .
72 By default the buffer contains 2048 entries.
74 For debugging purposes, the following
76 related kernel options exist:
77 .Bl -tag -width ".Dv KTR_SPIN_CONTENTION"
84 .Fn ether_input_dispatch
87 interrupts and sent/received packets
90 interrupts, polling and sent/received packets
92 classic ifq dequeue/enqueue operation
94 running/avoiding/scheduling ifnet.if_start
96 IPI related data (IPI requests, CPU synchronization etc.)
98 entry of the kernel from userland (faults, syscalls)
107 .It Dv KTR_SERIALIZER
110 .It Dv KTR_SPIN_CONTENTION
114 IPI performance testing
116 LWKT token related events
117 .It Dv KTR_USB_MEMORY
118 USB memory allocation
123 By default, events are only logged to the internal buffer for examination
124 later, but if the verbose flag is set then they are dumped to the kernel
126 This flag can also be set from the loader via the
127 .Va debug.ktr.verbose
128 environment variable, or it can be examined and set after booting via the
129 .Va debug.ktr.verbose
131 If the flag is set to zero, which is the default, then verbose output is
133 If the flag is set to one, then the contents of the log message and the CPU
134 number are printed to the kernel console.
135 If the flag is greater than one, then the filename and line number of the
136 event are output to the console in addition to the log message and the CPU
140 option enables verbose mode and sets the flag to one.
141 .Ss Examining the Events
142 The KTR buffer can be examined with
148 .Ic show ktr Op Cm /v
150 This command displays the contents of the trace buffer one page at a time.
153 prompt, the Enter key displays one more entry and prompts again.
154 The spacebar displays another page of entries.
156 By default the timestamp, filename, and line number are not displayed with
160 modifier is specified, then they are displayed in addition to the normal
162 Note that the events are displayed in reverse chronological order.
163 That is, the most recent events are displayed first.
170 The KTR kernel tracing facility first appeared in
172 and was imported into
176 It was completely rewritten by Matthew Dillon in