man/man4/ktr.4

.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $
.\" $DragonFly: src/share/man/man4/ktr.4,v 1.4 2007/11/03 07:24:52 swildner Exp $
.\"
.Dd November 2, 2007
.Dt KTR 4
.Os
.Sh NAME
.Nm ktr
.Nd kernel tracing facility
.Sh SYNOPSIS
.Cd options KTR
.Cd options KTR_ENTRIES=8192
.Cd options KTR_VERBOSE=1
.Cd options KTR_ALL
.Cd options KTR_GIANT_CONTENTION
.Cd options KTR_IF_BGE
.Cd options KTR_IF_EM
.Cd options KTR_IPIQ
.Cd options KTR_MEMORY
.Cd options KTR_SPIN_CONTENTION
.\".Cd options KTR_TCP
.\".Cd options KTR_TESTLOG
.Cd options KTR_TOKENS
.\".Cd options KTR_TSLEEP
.Cd options KTR_USB_MEMORY
.Sh DESCRIPTION
The
.Nm
facility allows kernel events to be logged while the kernel executes so that
they can be examined later when debugging.
The only mandatory option to enable
.Nm
is
.Cd options KTR .
.Pp
The
.Dv KTR_ENTRIES
option sets the size of the buffer of events.
It should be a power of two.
The size of the buffer in the currently running kernel can be found via the
read-only sysctl
.Va debug.ktr.entries .
By default the buffer contains 2048 entries.
.Pp
For debugging purposes, the following
.Nm
related kernel options exist:
.Bl -tag -width ".Dv KTR_GIANT_CONTENTION"
.It Dv KTR_ALL
turns on all options
.It Dv KTR_GIANT_CONTENTION
contention of the giant lock
.It Dv KTR_IF_BGE
.Xr bge 4
interrupts and sent/received packets
.It Dv KTR_IF_EM
.Xr em 4
interrupts, polling and sent/received packets
.It Dv KTR_IPIQ
IPI related data (IPI requests, CPU synchronization etc.)
.It Dv KTR_MEMORY
.Xr kmalloc 9
and
.Xr kfree 9
events
.It Dv KTR_SPIN_CONTENTION
.Xr spinlock 9
contention
.It Dv KTR_TOKENS
LWKT token related events
.It Dv KTR_USB_MEMORY
USB memory allocation
.El
.Ss Verbose Mode
By default, events are only logged to the internal buffer for examination
later, but if the verbose flag is set then they are dumped to the kernel
console as well.
This flag can also be set from the loader via the
.Va debug.ktr.verbose
environment variable, or it can be examined and set after booting via the
.Va debug.ktr.verbose
sysctl.
If the flag is set to zero, which is the default, then verbose output is
disabled.
If the flag is set to one, then the contents of the log message and the CPU
number are printed to the kernel console.
If the flag is greater than one, then the filename and line number of the
event are output to the console in addition to the log message and the CPU
number.
The
.Dv KTR_VERBOSE
option sets the flag to one.
.Ss Examining the Events
The KTR buffer can be examined with
.Xr ktrdump 8 ,
.Xr gdb 1
or from within
.Xr ddb 4
via the
.Ic show ktr Op Cm /v
command.
This command displays the contents of the trace buffer one page at a time.
At the
.Dq Li --more--
prompt, the Enter key displays one more entry and prompts again.
The spacebar displays another page of entries.
Any other key quits.
By default the timestamp, filename, and line number are not displayed with
each log entry.
If the
.Cm /v
modifier is specified, then they are displayed in addition to the normal
output.
Note that the events are displayed in reverse chronological order.
That is, the most recent events are displayed first.
.Sh SEE ALSO
.Xr gdb 1 ,
.Xr ddb 4 ,
.Xr ktrdump 8 ,
.Xr ktr 9
.Sh HISTORY
The KTR kernel tracing facility first appeared in
.Bsx 3.0
and was imported into
.Fx 5.0
and
.Dx 1.1 .
It was completely rewritten by Matthew Dillon in
.Dx 1.3 .