xref: /dragonfly/share/man/man4/ktr.4 (revision 10cbe914) 
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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 1.11 2008/10/01 10:53:48 swildner Exp $
27.\"
28.Dd October 1, 2008
29.Dt KTR 4
30.Os
31.Sh NAME
32.Nm ktr
33.Nd kernel tracing facility
34.Sh SYNOPSIS
35.Cd options KTR
36.Cd options KTR_ENTRIES=8192
37.Cd options KTR_VERBOSE=1
38.Cd options KTR_ALL
39.Cd options KTR_ETHERNET
40.Cd options KTR_IF_BGE
41.Cd options KTR_IF_EM
42.Cd options KTR_IF_START
43.Cd options KTR_IFQ
44.Cd options KTR_IPIQ
45.Cd options KTR_KERNENTRY
46.Cd options KTR_MEMORY
47.Cd options KTR_POLLING
48.Cd options KTR_SERIALIZER
49.Cd options KTR_SPIN_CONTENTION
50.\".Cd options KTR_TCP
51.Cd options KTR_TESTLOG
52.Cd options KTR_TOKENS
53.\".Cd options KTR_TSLEEP
54.Cd options KTR_USB_MEMORY
55.Cd options KTR_CTXSW
56.Sh DESCRIPTION
57The
58.Nm
59facility allows kernel events to be logged while the kernel executes so that
60they can be examined later when debugging.
61The only mandatory option to enable
62.Nm
63is
64.Cd options KTR .
65.Pp
66The
67.Dv KTR_ENTRIES
68option sets the size of the buffer of events.
69It should be a power of two.
70The size of the buffer in the currently running kernel can be found via the
71read-only sysctl
72.Va debug.ktr.entries .
73By default the buffer contains 2048 entries.
74.Pp
75For debugging purposes, the following
76.Nm
77related kernel options exist:
78.Bl -tag -width ".Dv KTR_SPIN_CONTENTION"
79.It Dv KTR_ALL
80turns on all options
81.It Dv KTR_ETHERNET
82cost of
83.Fn ether_input_chain
84and
85.Fn ether_input_dispatch
86.It Dv KTR_IF_BGE
87.Xr bge 4
88interrupts and sent/received packets
89.It Dv KTR_IF_EM
90.Xr em 4
91interrupts, polling and sent/received packets
92.It Dv KTR_IFQ
93classic ifq dequeue/enqueue operation
94.It Dv KTR_IF_START
95running/avoiding/scheduling ifnet.if_start
96.It Dv KTR_IPIQ
97IPI related data (IPI requests, CPU synchronization etc.)
98.It Dv KTR_KERNENTRY
99entry of the kernel from userland (faults, syscalls)
100.It Dv KTR_MEMORY
101.Xr kmalloc 9
102and
103.Xr kfree 9
104events
105.It Dv KTR_POLLING
106.Xr polling 4
107begins and ends
108.It Dv KTR_SERIALIZER
109.Xr serializer 9
110related events
111.It Dv KTR_SPIN_CONTENTION
112.Xr spinlock 9
113contention
114.It Dv KTR_TESTLOG
115IPI performance testing
116.It Dv KTR_TOKENS
117LWKT token related events
118.It Dv KTR_USB_MEMORY
119USB memory allocation
120.It Dv KTR_CTXSW
121context switches
122.El
123.Ss Verbose Mode
124By default, events are only logged to the internal buffer for examination
125later, but if the verbose flag is set then they are dumped to the kernel
126console as well.
127This flag can also be set from the loader via the
128.Va debug.ktr.verbose
129environment variable, or it can be examined and set after booting via the
130.Va debug.ktr.verbose
131sysctl.
132If the flag is set to zero, which is the default, then verbose output is
133disabled.
134If the flag is set to one, then the contents of the log message and the CPU
135number are printed to the kernel console.
136If the flag is greater than one, then the filename and line number of the
137event are output to the console in addition to the log message and the CPU
138number.
139The
140.Dv KTR_VERBOSE
141option enables verbose mode and sets the flag to one.
142.Ss Examining the Events
143The KTR buffer can be examined with
144.Xr ktrdump 8 ,
145.Xr gdb 1
146or from within
147.Xr ddb 4
148via the
149.Ic show ktr Op Cm /v
150command.
151This command displays the contents of the trace buffer one page at a time.
152At the
153.Dq Li --more--
154prompt, the Enter key displays one more entry and prompts again.
155The spacebar displays another page of entries.
156Any other key quits.
157By default the timestamp, filename, and line number are not displayed with
158each log entry.
159If the
160.Cm /v
161modifier is specified, then they are displayed in addition to the normal
162output.
163Note that the events are displayed in reverse chronological order.
164That is, the most recent events are displayed first.
165.Sh SEE ALSO
166.Xr gdb 1 ,
167.Xr ddb 4 ,
168.Xr ktrdump 8 ,
169.Xr ktr 9
170.Sh HISTORY
171The KTR kernel tracing facility first appeared in
172.Bsx 3.0
173and was imported into
174.Fx 5.0
175and
176.Dx 1.1 .
177It was completely rewritten by Matthew Dillon in
178.Dx 1.3 .
179