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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
39 .Cd options KTR_ETHERNET
40 .\".Cd options KTR_HAMMER
41 .Cd options KTR_IF_BGE
43 .Cd options KTR_IF_EMX
44 .Cd options KTR_IF_START
47 .Cd options KTR_KERNENTRY
48 .Cd options KTR_MEMORY
49 .Cd options KTR_POLLING
50 .Cd options KTR_SERIALIZER
51 .Cd options KTR_SPIN_CONTENTION
52 .\".Cd options KTR_TCP
53 .Cd options KTR_TESTLOG
54 .Cd options KTR_TOKENS
55 .\".Cd options KTR_TSLEEP
56 .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 must 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_SPIN_CONTENTION"
88 .Fn ether_input_dispatch
91 interrupts and sent/received packets
94 interrupts and sent/received packets
97 interrupts and sent/received packets
99 classic ifq dequeue/enqueue operation
101 running/avoiding/scheduling ifnet.if_start
103 IPI related data (IPI requests, CPU synchronization etc.)
105 entry of the kernel from userland (faults, syscalls)
114 .It Dv KTR_SERIALIZER
117 .It Dv KTR_SPIN_CONTENTION
121 IPI performance testing
123 LWKT token related events
124 .It Dv KTR_USB_MEMORY
125 USB memory allocation
128 By default, events are only logged to the internal buffer for examination
129 later, but if the verbose flag is set then they are dumped to the kernel
131 This flag can also be set from the loader via the
132 .Va debug.ktr.verbose
133 environment variable, or it can be examined and set after booting via the
134 .Va debug.ktr.verbose
136 If the flag is set to zero, which is the default, then verbose output is
138 If the flag is set to one, then the contents of the log message and the CPU
139 number are printed to the kernel console.
140 If the flag is greater than one, then the filename and line number of the
141 event are output to the console in addition to the log message and the CPU
145 option enables verbose mode and sets the flag to one.
146 .Ss Examining the Events
147 The KTR buffer can be examined with
153 .Ic show ktr Op Cm /v
155 This command displays the contents of the trace buffer one page at a time.
158 prompt, the Enter key displays one more entry and prompts again.
159 The spacebar displays another page of entries.
161 By default the timestamp, filename, and line number are not displayed with
165 modifier is specified, then they are displayed in addition to the normal
167 Note that the events are displayed in reverse chronological order.
168 That is, the most recent events are displayed first.
170 .Bl -tag -width ".Va debug.ktr.*_enable"
171 .It Va debug.ktr.*_enable
172 A 32 bit mask used to control event logging.
173 Each bit corresponds to one or more events depending on the values of the
175 parameters that were passed to the
177 calls which declared the events.
181 is specified in the kernel configuration, the default is to turn on logging
182 for all corresponding events (i.e.\& setting the sysctl to -1).
183 .It Va debug.ktr.*_mask
184 Read only sysctls (one per event) that show the
185 .Va debug.ktr.*_enable
186 values corresponding to the events.
194 The KTR kernel tracing facility first appeared in
196 and was imported into
200 It was completely rewritten by Matthew Dillon in