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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_ACPI_EC
40 .Cd options KTR_DMCRYPT
41 .Cd options KTR_ETHERNET
42 .\".Cd options KTR_HAMMER
43 .Cd options KTR_IF_BGE
45 .Cd options KTR_IF_EMX
46 .Cd options KTR_IF_POLL
47 .Cd options KTR_IF_START
50 .Cd options KTR_KERNENTRY
51 .Cd options KTR_MEMORY
52 .Cd options KTR_SERIALIZER
53 .Cd options KTR_SPIN_CONTENTION
54 .\".Cd options KTR_TCP
55 .Cd options KTR_TESTLOG
56 .Cd options KTR_TOKENS
57 .Cd options KTR_TSLEEP
58 .Cd options KTR_USCHED_BSD4
59 .Cd options KTR_USCHED_DFLY
63 facility allows kernel events to be logged while the kernel executes so that
64 they can be examined later when debugging.
65 The only mandatory option to enable
72 option sets the size of the buffer of events.
73 It must be a power of two.
74 The size of the buffer in the currently running kernel can be found via the
76 .Va debug.ktr.entries .
77 By default the buffer contains 2048 entries.
79 For debugging purposes, the following
81 related kernel options exist:
82 .Bl -tag -width ".Dv KTR_SPIN_CONTENTION"
86 ACPI Embedded Controller related data
90 read and write strategy paths of
101 interrupts and sent/received packets
104 interrupts and sent/received packets
107 interrupts and sent/received packets
109 classic ifq dequeue/enqueue operation
114 running/avoiding/scheduling ifnet.if_start
116 IPI related data (IPI requests, CPU synchronization etc.)
118 entry of the kernel from userland (faults, syscalls)
124 .It Dv KTR_SERIALIZER
127 .It Dv KTR_SPIN_CONTENTION
131 IPI performance testing
133 LWKT token related events
138 .It Dv KTR_USCHED_BSD4
139 usched_bsd4 scheduling decisions
140 .It Dv KTR_USCHED_DFLY
141 usched_dfly scheduling decisions
144 By default, events are only logged to the internal buffer for examination
145 later, but if the verbose flag is set then they are dumped to the kernel
147 This flag can also be set from the loader via the
148 .Va debug.ktr.verbose
149 environment variable, or it can be examined and set after booting via the
150 .Va debug.ktr.verbose
152 If the flag is set to zero, which is the default, then verbose output is
154 If the flag is set to one, then the contents of the log message and the CPU
155 number are printed to the kernel console.
156 If the flag is greater than one, then the filename and line number of the
157 event are output to the console in addition to the log message and the CPU
161 option enables verbose mode and sets the flag to one.
162 .Ss Examining the Events
163 The KTR buffer can be examined with
169 .Ic show ktr Op Cm /v
171 This command displays the contents of the trace buffer one page at a time.
174 prompt, the Enter key displays one more entry and prompts again.
175 The spacebar displays another page of entries.
177 By default the timestamp, filename, and line number are not displayed with
181 modifier is specified, then they are displayed in addition to the normal
183 Note that the events are displayed in reverse chronological order.
184 That is, the most recent events are displayed first.
186 .Bl -tag -width ".Va debug.ktr.resynchronize"
187 .It Va debug.ktr.*_enable
188 A 32 bit mask used to control event logging.
189 Each bit corresponds to one or more events depending on the values of the
191 parameters that were passed to the
193 calls which declared the events.
197 is specified in the kernel configuration, the default is to turn on logging
198 for all corresponding events (i.e.\& setting the sysctl to -1).
199 .It Va debug.ktr.*_mask
200 Read only sysctls (one per event) that show the
201 .Va debug.ktr.*_enable
202 values corresponding to the events.
203 .It Va debug.ktr.resynchronize
204 Resynchronize the TSC across all CPUs 10 times per second in an attempt to
206 Note that this is very expensive and therefore the default is 0.
214 The KTR kernel tracing facility first appeared in
216 and was imported into
220 It was completely rewritten by Matthew Dillon in