usr.bin/ktrdump/ktrdump.8

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.\" $FreeBSD: src/usr.bin/ktrdump/ktrdump.8,v 1.7 2005/03/08 06:58:56 hmp Exp $
.\" $DragonFly: src/usr.bin/ktrdump/ktrdump.8,v 1.16 2008/11/10 02:05:31 swildner Exp $
.\"
.Dd November 9, 2008
.Dt KTRDUMP 8
.Os
.Sh NAME
.Nm ktrdump
.Nd print kernel ktr trace buffer
.Sh SYNOPSIS
.Nm
.Op Fl acfilnpqrstx
.Op Fl A Ar factor
.Op Fl N Ar execfile
.Op Fl M Ar corefile
.Op Fl o Ar outfile
.Sh DESCRIPTION
The
.Nm
utility is used to dump the contents of the kernel ktr trace buffer.
.Pp
The following options are available:
.Bl -tag -width ".Fl N Ar execfile"
.It Fl a
Print most fields.
Implies
.Fl c
.Fl i
.Fl x
.Fl p
.Fl r ,
and
.Fl s .
Note that
.Fl f
is not included.
.It Fl c
Print the CPU number that each entry was logged from.
.It Fl f
Print the file and line number that each entry was logged from.
.It Fl i
Print the ID string field, identifying the facility being logged.
.It Fl l
.Nm
will loop waiting for new data rather than exit.
.It Fl n
.Nm
normally tries to translate the caller fields and (when easily parsed)
trace arguments into symbols.
This option forces hex values to be displayed instead.
This option will also cause relative timestamps to
be displayed as TSC timestamps rather than converted to microseconds.
.It Fl p
Print the trace data.
.It Fl q
Quiet mode; do not print the column header.
.It Fl r
Print relative timestamps in microseconds, rather than absolute TSC
timestamps.
.It Fl s
Attempt to merge the KTR logs for all cpus into a single time-sorted
log.
For the numbers to make any sense you probably want to turn on the
.Va debug.ktr.resynchronize
.Xr sysctl 3
variable.
This sysctl causes the kernel to periodically
calculate the drift between each CPU's TSC and apply a correction.
.It Fl t
Print the timestamp for each entry.
.It Fl x
Print the call chain leading up to the procedure which issued
the KTR.
.It Fl A Ar factor
Specify a correction factor to be applied to attempt to remove the
overhead of the KTR logging call itself.
.It Fl N Ar execfile
The kernel image to resolve symbols from.
The default is the value returned via
.Xr getbootfile 3 .
.It Fl M Ar corefile
The core file or memory image to read from.
The default is
.Pa /dev/mem .
.It Fl o Ar outfile
The file to write the output to.
The default is standard output.
.El
.Sh OPERATIONAL NOTES
Users of
.Nm
should keep in mind that the act of trace logging will itself affect
execution overheads.
On a 2Ghz cpu a logging call can take anywhere from 40ns to 150ns to run.
.Pp
The TSC counter is used on cpus equipped with it (which is all modern cpus).
The TSC counters may not be synchronized on SMP systems and may drift even
between cores on multi-core cpus.
Enabling synchronization between cpus via the
.Va debug.ktr.resynchronize
sysctl will impose additional system overheads and will generally only be
accurate to within 100ns or so (and perhaps not even that good).
Resynchronization only occurs 10 times a second and serious drift will
cause a great deal of measurement noise when trying to compare events occurring
on two different cpus.
.Pp
Users using the
.Fl s
option should be aware that events for each cpu are independently logged
and one cpu might have more events logged then another, causing earlier
events to be discarded sooner then other cpus.
The beginning portion of
the sorted output may thus show MP related events for one cpu with no
corresponding events for other cpus.
.Pp
It is possible to somewhat characterize KTR logging overheads by setting
the
.Va debug.ktr.testlogcnt
sysctl and then observing test logging events in the KTR output.
Tests 1-3 log four dummy arguments while tests 4-6 log no arguments.
.Pp
It is possible to characterize IPI messaging latencies by setting the
.Va debug.ktr.testipicnt
sysctl.
A small number between 1 and 1000 is recommended.
This will
cause the system to ping pong a single IPI message between cpu 0 and cpu 1
asynchronously that number of times, as fast as it can.
A
.Nm
should be performed almost immediately after setting the sysctl or you
might miss the logged events.
.Sh SEE ALSO
.Xr ktr 4 ,
.Xr ktr 9
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 5.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
utility was originally implemented by
.An Jake Burkholder Aq jake@FreeBSD.org .
This manual page was originally written by
.An Chad David Aq davidc@FreeBSD.org .
The program and manual page were rewritten pretty much from
scratch by
.An Matthew Dillon
for
.Dx .