xref: /dragonfly/share/man/man4/ktr.4 (revision dcd37f7d) 
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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_GIANT_CONTENTION
41.Cd options KTR_IF_BGE
42.Cd options KTR_IF_EM
43.Cd options KTR_IF_START
44.Cd options KTR_IFQ
45.Cd options KTR_IPIQ
46.Cd options KTR_KERNENTRY
47.Cd options KTR_MEMORY
48.Cd options KTR_POLLING
49.Cd options KTR_SERIALIZER
50.Cd options KTR_SPIN_CONTENTION
51.\".Cd options KTR_TCP
52.Cd options KTR_TESTLOG
53.Cd options KTR_TOKENS
54.\".Cd options KTR_TSLEEP
55.Cd options KTR_USB_MEMORY
56.Cd options KTR_CTXSW
57.Sh DESCRIPTION
58The
59.Nm
60facility allows kernel events to be logged while the kernel executes so that
61they can be examined later when debugging.
62The only mandatory option to enable
63.Nm
64is
65.Cd options KTR .
66.Pp
67The
68.Dv KTR_ENTRIES
69option sets the size of the buffer of events.
70It should be a power of two.
71The size of the buffer in the currently running kernel can be found via the
72read-only sysctl
73.Va debug.ktr.entries .
74By default the buffer contains 2048 entries.
75.Pp
76For debugging purposes, the following
77.Nm
78related kernel options exist:
79.Bl -tag -width ".Dv KTR_GIANT_CONTENTION"
80.It Dv KTR_ALL
81turns on all options
82.It Dv KTR_ETHERNET
83cost of
84.Fn ether_input_chain
85and
86.Fn ether_input_dispatch
87.It Dv KTR_GIANT_CONTENTION
88contention of the giant lock
89.It Dv KTR_IF_BGE
90.Xr bge 4
91interrupts and sent/received packets
92.It Dv KTR_IF_EM
93.Xr em 4
94interrupts, polling and sent/received packets
95.It Dv KTR_IFQ
96classic ifq dequeue/enqueue operation
97.It Dv KTR_IF_START
98running/avoiding/scheduling ifnet.if_start
99.It Dv KTR_IPIQ
100IPI related data (IPI requests, CPU synchronization etc.)
101.It Dv KTR_KERNENTRY
102entry of the kernel from userland (faults, syscalls)
103.It Dv KTR_MEMORY
104.Xr kmalloc 9
105and
106.Xr kfree 9
107events
108.It Dv KTR_POLLING
109.Xr polling 4
110begins and ends
111.It Dv KTR_SERIALIZER
112.Xr serializer 9
113related events
114.It Dv KTR_SPIN_CONTENTION
115.Xr spinlock 9
116contention
117.It Dv KTR_TESTLOG
118IPI performance testing
119.It Dv KTR_TOKENS
120LWKT token related events
121.It Dv KTR_USB_MEMORY
122USB memory allocation
123.It Dv KTR_CTXSW
124context switches
125.El
126.Ss Verbose Mode
127By default, events are only logged to the internal buffer for examination
128later, but if the verbose flag is set then they are dumped to the kernel
129console as well.
130This flag can also be set from the loader via the
131.Va debug.ktr.verbose
132environment variable, or it can be examined and set after booting via the
133.Va debug.ktr.verbose
134sysctl.
135If the flag is set to zero, which is the default, then verbose output is
136disabled.
137If the flag is set to one, then the contents of the log message and the CPU
138number are printed to the kernel console.
139If the flag is greater than one, then the filename and line number of the
140event are output to the console in addition to the log message and the CPU
141number.
142The
143.Dv KTR_VERBOSE
144option enables verbose mode and sets the flag to one.
145.Ss Examining the Events
146The KTR buffer can be examined with
147.Xr ktrdump 8 ,
148.Xr gdb 1
149or from within
150.Xr ddb 4
151via the
152.Ic show ktr Op Cm /v
153command.
154This command displays the contents of the trace buffer one page at a time.
155At the
156.Dq Li --more--
157prompt, the Enter key displays one more entry and prompts again.
158The spacebar displays another page of entries.
159Any other key quits.
160By default the timestamp, filename, and line number are not displayed with
161each log entry.
162If the
163.Cm /v
164modifier is specified, then they are displayed in addition to the normal
165output.
166Note that the events are displayed in reverse chronological order.
167That is, the most recent events are displayed first.
168.Sh SEE ALSO
169.Xr gdb 1 ,
170.Xr ddb 4 ,
171.Xr ktrdump 8 ,
172.Xr ktr 9
173.Sh HISTORY
174The KTR kernel tracing facility first appeared in
175.Bsx 3.0
176and was imported into
177.Fx 5.0
178and
179.Dx 1.1 .
180It was completely rewritten by Matthew Dillon in
181.Dx 1.3 .
182