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 1.4 2007/11/03 07:24:52 swildner Exp $
33 .Nd kernel tracing facility
36 .Cd options KTR_ENTRIES=8192
37 .Cd options KTR_VERBOSE=1
39 .Cd options KTR_GIANT_CONTENTION
40 .Cd options KTR_IF_BGE
43 .Cd options KTR_MEMORY
44 .Cd options KTR_SPIN_CONTENTION
45 .\".Cd options KTR_TCP
46 .\".Cd options KTR_TESTLOG
47 .Cd options KTR_TOKENS
48 .\".Cd options KTR_TSLEEP
49 .Cd options KTR_USB_MEMORY
53 facility allows kernel events to be logged while the kernel executes so that
54 they can be examined later when debugging.
55 The only mandatory option to enable
62 option sets the size of the buffer of events.
63 It should be a power of two.
64 The size of the buffer in the currently running kernel can be found via the
66 .Va debug.ktr.entries .
67 By default the buffer contains 2048 entries.
69 For debugging purposes, the following
71 related kernel options exist:
72 .Bl -tag -width ".Dv KTR_GIANT_CONTENTION"
75 .It Dv KTR_GIANT_CONTENTION
76 contention of the giant lock
79 interrupts and sent/received packets
82 interrupts, polling and sent/received packets
84 IPI related data (IPI requests, CPU synchronization etc.)
90 .It Dv KTR_SPIN_CONTENTION
94 LWKT token related events
99 By default, events are only logged to the internal buffer for examination
100 later, but if the verbose flag is set then they are dumped to the kernel
102 This flag can also be set from the loader via the
103 .Va debug.ktr.verbose
104 environment variable, or it can be examined and set after booting via the
105 .Va debug.ktr.verbose
107 If the flag is set to zero, which is the default, then verbose output is
109 If the flag is set to one, then the contents of the log message and the CPU
110 number are printed to the kernel console.
111 If the flag is greater than one, then the filename and line number of the
112 event are output to the console in addition to the log message and the CPU
116 option sets the flag to one.
117 .Ss Examining the Events
118 The KTR buffer can be examined with
124 .Ic show ktr Op Cm /v
126 This command displays the contents of the trace buffer one page at a time.
129 prompt, the Enter key displays one more entry and prompts again.
130 The spacebar displays another page of entries.
132 By default the timestamp, filename, and line number are not displayed with
136 modifier is specified, then they are displayed in addition to the normal
138 Note that the events are displayed in reverse chronological order.
139 That is, the most recent events are displayed first.
146 The KTR kernel tracing facility first appeared in
148 and was imported into
152 It was completely rewritten by Matthew Dillon in