1 .\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org>
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25 .\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $
26 .\" $DragonFly: src/share/man/man4/ktr.4,v 1.11 2008/10/01 10:53:48 swildner Exp $
33 .Nd kernel tracing facility
36 .Cd options KTR_ENTRIES=8192
37 .Cd options KTR_VERBOSE=1
39 .Cd options KTR_ETHERNET
40 .Cd options KTR_GIANT_CONTENTION
41 .Cd options KTR_IF_BGE
43 .Cd options KTR_IF_START
46 .Cd options KTR_KERNENTRY
47 .Cd options KTR_MEMORY
48 .Cd options KTR_POLLING
49 .Cd options KTR_SERIALIZER
50 .Cd options KTR_SPIN_CONTENTION
51 .\".Cd options KTR_TCP
52 .Cd options KTR_TESTLOG
53 .Cd options KTR_TOKENS
54 .\".Cd options KTR_TSLEEP
55 .Cd options KTR_USB_MEMORY
60 facility allows kernel events to be logged while the kernel executes so that
61 they can be examined later when debugging.
62 The only mandatory option to enable
69 option sets the size of the buffer of events.
70 It should be a power of two.
71 The size of the buffer in the currently running kernel can be found via the
73 .Va debug.ktr.entries .
74 By default the buffer contains 2048 entries.
76 For debugging purposes, the following
78 related kernel options exist:
79 .Bl -tag -width ".Dv KTR_GIANT_CONTENTION"
86 .Fn ether_input_dispatch
87 .It Dv KTR_GIANT_CONTENTION
88 contention of the giant lock
91 interrupts and sent/received packets
94 interrupts, polling and sent/received packets
96 classic ifq dequeue/enqueue operation
98 running/avoiding/scheduling ifnet.if_start
100 IPI related data (IPI requests, CPU synchronization etc.)
102 entry of the kernel from userland (faults, syscalls)
111 .It Dv KTR_SERIALIZER
114 .It Dv KTR_SPIN_CONTENTION
118 IPI performance testing
120 LWKT token related events
121 .It Dv KTR_USB_MEMORY
122 USB memory allocation
127 By default, events are only logged to the internal buffer for examination
128 later, but if the verbose flag is set then they are dumped to the kernel
130 This flag can also be set from the loader via the
131 .Va debug.ktr.verbose
132 environment variable, or it can be examined and set after booting via the
133 .Va debug.ktr.verbose
135 If the flag is set to zero, which is the default, then verbose output is
137 If the flag is set to one, then the contents of the log message and the CPU
138 number are printed to the kernel console.
139 If the flag is greater than one, then the filename and line number of the
140 event are output to the console in addition to the log message and the CPU
144 option enables verbose mode and sets the flag to one.
145 .Ss Examining the Events
146 The KTR buffer can be examined with
152 .Ic show ktr Op Cm /v
154 This command displays the contents of the trace buffer one page at a time.
157 prompt, the Enter key displays one more entry and prompts again.
158 The spacebar displays another page of entries.
160 By default the timestamp, filename, and line number are not displayed with
164 modifier is specified, then they are displayed in addition to the normal
166 Note that the events are displayed in reverse chronological order.
167 That is, the most recent events are displayed first.
174 The KTR kernel tracing facility first appeared in
176 and was imported into
180 It was completely rewritten by Matthew Dillon in