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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_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_POLLING
51 .Cd options KTR_SERIALIZER
52 .Cd options KTR_SPIN_CONTENTION
53 .\".Cd options KTR_TCP
54 .Cd options KTR_TESTLOG
55 .Cd options KTR_TOKENS
56 .Cd options KTR_TSLEEP
57 .Cd options KTR_USB_MEMORY
58 .Cd options KTR_USCHED_BSD4
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)
121 .It Dv KTR_SERIALIZER
124 .It Dv KTR_SPIN_CONTENTION
128 IPI performance testing
130 LWKT token related events
135 .It Dv KTR_USB_MEMORY
136 USB memory allocation
137 .It Dv KTR_USCHED_BSD4
138 usched_bsd4 scheduling decisions
141 By default, events are only logged to the internal buffer for examination
142 later, but if the verbose flag is set then they are dumped to the kernel
144 This flag can also be set from the loader via the
145 .Va debug.ktr.verbose
146 environment variable, or it can be examined and set after booting via the
147 .Va debug.ktr.verbose
149 If the flag is set to zero, which is the default, then verbose output is
151 If the flag is set to one, then the contents of the log message and the CPU
152 number are printed to the kernel console.
153 If the flag is greater than one, then the filename and line number of the
154 event are output to the console in addition to the log message and the CPU
158 option enables verbose mode and sets the flag to one.
159 .Ss Examining the Events
160 The KTR buffer can be examined with
166 .Ic show ktr Op Cm /v
168 This command displays the contents of the trace buffer one page at a time.
171 prompt, the Enter key displays one more entry and prompts again.
172 The spacebar displays another page of entries.
174 By default the timestamp, filename, and line number are not displayed with
178 modifier is specified, then they are displayed in addition to the normal
180 Note that the events are displayed in reverse chronological order.
181 That is, the most recent events are displayed first.
183 .Bl -tag -width ".Va debug.ktr.resynchronize"
184 .It Va debug.ktr.*_enable
185 A 32 bit mask used to control event logging.
186 Each bit corresponds to one or more events depending on the values of the
188 parameters that were passed to the
190 calls which declared the events.
194 is specified in the kernel configuration, the default is to turn on logging
195 for all corresponding events (i.e.\& setting the sysctl to -1).
196 .It Va debug.ktr.*_mask
197 Read only sysctls (one per event) that show the
198 .Va debug.ktr.*_enable
199 values corresponding to the events.
200 .It Va debug.ktr.resynchronize
201 Resynchronize the TSC across all CPUs 10 times per second in an attempt to
203 Note that this is very expensive and therefore the default is 0.
211 The KTR kernel tracing facility first appeared in
213 and was imported into
217 It was completely rewritten by Matthew Dillon in