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25 .\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $
27 .Dd September 18, 2012
32 .Nd kernel tracing facility
35 .Cd options KTR_ENTRIES=8192
36 .Cd options KTR_VERBOSE=1
39 .Cd options KTR_DMCRYPT
40 .Cd options KTR_ETHERNET
41 .\".Cd options KTR_HAMMER
42 .Cd options KTR_IF_BGE
44 .Cd options KTR_IF_EMX
45 .Cd options KTR_IF_START
48 .Cd options KTR_KERNENTRY
49 .Cd options KTR_MEMORY
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
57 .Cd options KTR_USCHED_BSD4
58 .Cd options KTR_USCHED_DFLY
62 facility allows kernel events to be logged while the kernel executes so that
63 they can be examined later when debugging.
64 The only mandatory option to enable
71 option sets the size of the buffer of events.
72 It must be a power of two.
73 The size of the buffer in the currently running kernel can be found via the
75 .Va debug.ktr.entries .
76 By default the buffer contains 2048 entries.
78 For debugging purposes, the following
80 related kernel options exist:
81 .Bl -tag -width ".Dv KTR_SPIN_CONTENTION"
87 read and write strategy paths of
98 interrupts and sent/received packets
101 interrupts and sent/received packets
104 interrupts and sent/received packets
106 classic ifq dequeue/enqueue operation
108 running/avoiding/scheduling ifnet.if_start
110 IPI related data (IPI requests, CPU synchronization etc.)
112 entry of the kernel from userland (faults, syscalls)
118 .It Dv KTR_SERIALIZER
121 .It Dv KTR_SPIN_CONTENTION
125 IPI performance testing
127 LWKT token related events
132 .It Dv KTR_USB_MEMORY
133 USB memory allocation
134 .It Dv KTR_USCHED_BSD4
135 usched_bsd4 scheduling decisions
136 .It Dv KTR_USCHED_DFLY
137 usched_dfly scheduling decisions
140 By default, events are only logged to the internal buffer for examination
141 later, but if the verbose flag is set then they are dumped to the kernel
143 This flag can also be set from the loader via the
144 .Va debug.ktr.verbose
145 environment variable, or it can be examined and set after booting via the
146 .Va debug.ktr.verbose
148 If the flag is set to zero, which is the default, then verbose output is
150 If the flag is set to one, then the contents of the log message and the CPU
151 number are printed to the kernel console.
152 If the flag is greater than one, then the filename and line number of the
153 event are output to the console in addition to the log message and the CPU
157 option enables verbose mode and sets the flag to one.
158 .Ss Examining the Events
159 The KTR buffer can be examined with
165 .Ic show ktr Op Cm /v
167 This command displays the contents of the trace buffer one page at a time.
170 prompt, the Enter key displays one more entry and prompts again.
171 The spacebar displays another page of entries.
173 By default the timestamp, filename, and line number are not displayed with
177 modifier is specified, then they are displayed in addition to the normal
179 Note that the events are displayed in reverse chronological order.
180 That is, the most recent events are displayed first.
182 .Bl -tag -width ".Va debug.ktr.resynchronize"
183 .It Va debug.ktr.*_enable
184 A 32 bit mask used to control event logging.
185 Each bit corresponds to one or more events depending on the values of the
187 parameters that were passed to the
189 calls which declared the events.
193 is specified in the kernel configuration, the default is to turn on logging
194 for all corresponding events (i.e.\& setting the sysctl to -1).
195 .It Va debug.ktr.*_mask
196 Read only sysctls (one per event) that show the
197 .Va debug.ktr.*_enable
198 values corresponding to the events.
199 .It Va debug.ktr.resynchronize
200 Resynchronize the TSC across all CPUs 10 times per second in an attempt to
202 Note that this is very expensive and therefore the default is 0.
210 The KTR kernel tracing facility first appeared in
212 and was imported into
216 It was completely rewritten by Matthew Dillon in