xref: /dragonfly/share/man/man4/ktr.4 (revision cc93b0eb) 
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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 1.10 2008/05/22 04:00:43 swildner Exp $
27.\"
28.Dd May 22, 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_GIANT_CONTENTION
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.Sh DESCRIPTION
56The
57.Nm
58facility allows kernel events to be logged while the kernel executes so that
59they can be examined later when debugging.
60The only mandatory option to enable
61.Nm
62is
63.Cd options KTR .
64.Pp
65The
66.Dv KTR_ENTRIES
67option sets the size of the buffer of events.
68It should be a power of two.
69The size of the buffer in the currently running kernel can be found via the
70read-only sysctl
71.Va debug.ktr.entries .
72By default the buffer contains 2048 entries.
73.Pp
74For debugging purposes, the following
75.Nm
76related kernel options exist:
77.Bl -tag -width ".Dv KTR_GIANT_CONTENTION"
78.It Dv KTR_ALL
79turns on all options
80.It Dv KTR_GIANT_CONTENTION
81contention of the giant lock
82.It Dv KTR_IF_BGE
83.Xr bge 4
84interrupts and sent/received packets
85.It Dv KTR_IF_EM
86.Xr em 4
87interrupts, polling and sent/received packets
88.It Dv KTR_IFQ
89classic ifq dequeue/enqueue operation
90.It Dv KTR_IF_START
91running/avoiding/scheduling ifnet.if_start
92.It Dv KTR_IPIQ
93IPI related data (IPI requests, CPU synchronization etc.)
94.It Dv KTR_KERNENTRY
95entry of the kernel from userland (faults, syscalls)
96.It Dv KTR_MEMORY
97.Xr kmalloc 9
98and
99.Xr kfree 9
100events
101.It Dv KTR_POLLING
102.Xr polling 4
103begins and ends
104.It Dv KTR_SERIALIZER
105.Xr serializer 9
106related events
107.It Dv KTR_SPIN_CONTENTION
108.Xr spinlock 9
109contention
110.It Dv KTR_TESTLOG
111IPI performance testing
112.It Dv KTR_TOKENS
113LWKT token related events
114.It Dv KTR_USB_MEMORY
115USB memory allocation
116.El
117.Ss Verbose Mode
118By default, events are only logged to the internal buffer for examination
119later, but if the verbose flag is set then they are dumped to the kernel
120console as well.
121This flag can also be set from the loader via the
122.Va debug.ktr.verbose
123environment variable, or it can be examined and set after booting via the
124.Va debug.ktr.verbose
125sysctl.
126If the flag is set to zero, which is the default, then verbose output is
127disabled.
128If the flag is set to one, then the contents of the log message and the CPU
129number are printed to the kernel console.
130If the flag is greater than one, then the filename and line number of the
131event are output to the console in addition to the log message and the CPU
132number.
133The
134.Dv KTR_VERBOSE
135option enables verbose mode and sets the flag to one.
136.Ss Examining the Events
137The KTR buffer can be examined with
138.Xr ktrdump 8 ,
139.Xr gdb 1
140or from within
141.Xr ddb 4
142via the
143.Ic show ktr Op Cm /v
144command.
145This command displays the contents of the trace buffer one page at a time.
146At the
147.Dq Li --more--
148prompt, the Enter key displays one more entry and prompts again.
149The spacebar displays another page of entries.
150Any other key quits.
151By default the timestamp, filename, and line number are not displayed with
152each log entry.
153If the
154.Cm /v
155modifier is specified, then they are displayed in addition to the normal
156output.
157Note that the events are displayed in reverse chronological order.
158That is, the most recent events are displayed first.
159.Sh SEE ALSO
160.Xr gdb 1 ,
161.Xr ddb 4 ,
162.Xr ktrdump 8 ,
163.Xr ktr 9
164.Sh HISTORY
165The KTR kernel tracing facility first appeared in
166.Bsx 3.0
167and was imported into
168.Fx 5.0
169and
170.Dx 1.1 .
171It was completely rewritten by Matthew Dillon in
172.Dx 1.3 .
173