man/man4/ktr.4

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.\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $
.\"
.Dd February 18, 2019
.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_ACPI_EC
.Cd options KTR_CTXSW
.Cd options KTR_DMCRYPT
.Cd options KTR_ETHERNET
.\".Cd options KTR_HAMMER
.Cd options KTR_IF_BGE
.Cd options KTR_IF_EM
.Cd options KTR_IF_EMX
.Cd options KTR_IF_POLL
.Cd options KTR_IF_START
.Cd options KTR_IFQ
.Cd options KTR_IPIQ
.Cd options KTR_KERNENTRY
.Cd options KTR_LAPIC
.Cd options KTR_MEMORY
.Cd options KTR_SERIALIZER
.Cd options KTR_SPIN_CONTENTION
.\".Cd options KTR_TCP
.Cd options KTR_TESTLOG
.Cd options KTR_TOKENS
.Cd options KTR_TSLEEP
.Cd options KTR_USCHED_BSD4
.Cd options KTR_USCHED_DFLY
.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 must 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_SPIN_CONTENTION"
.It Dv KTR_ALL
turns on all options
.It Dv KTR_ACPI_EC
ACPI Embedded Controller related data
.It Dv KTR_CTXSW
context switches
.It Dv KTR_DMCRYPT
read and write strategy paths of
.Xr dm 4 Ap s
.Pa crypt
target
.It Dv KTR_ETHERNET
cost of
.Fn ether_input
and
.Fn ether_dispatch
.It Dv KTR_IF_BGE
.Xr bge 4
interrupts and sent/received packets
.It Dv KTR_IF_EM
.Xr em 4
interrupts and sent/received packets
.It Dv KTR_IF_EMX
.Xr emx 4
interrupts and sent/received packets
.It Dv KTR_IFQ
classic ifq dequeue/enqueue operation
.It Dv KTR_IF_POLL
.Xr polling 4
operation
.It Dv KTR_IF_START
running/avoiding/scheduling ifnet.if_start
.It Dv KTR_IPIQ
IPI related data (IPI requests, CPU synchronization etc.)
.It Dv KTR_LAPIC
Track LAPIC operation, for example EOI writes.
.It Dv KTR_KERNENTRY
entry of the kernel from userland (faults, syscalls)
.It Dv KTR_MEMORY
.Xr kmalloc 9
and
.Xr kfree 9
events
.It Dv KTR_SERIALIZER
.Xr serializer 9
related events
.It Dv KTR_SPIN_CONTENTION
.Xr spinlock 9
contention
.It Dv KTR_TESTLOG
IPI performance testing
.It Dv KTR_TOKENS
LWKT token related events
.It Dv KTR_TSLEEP
.Xr tsleep 9
and
.Xr wakeup 9
.It Dv KTR_USCHED_BSD4
usched_bsd4 scheduling decisions
.It Dv KTR_USCHED_DFLY
usched_dfly scheduling decisions
.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 enables verbose mode and 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 SYSCTL VARIABLES
.Bl -tag -width ".Va debug.ktr.resynchronize"
.It Va debug.ktr.*_enable
A 32 bit mask used to control event logging.
Each bit corresponds to one or more events depending on the values of the
.Fa maskbit
parameters that were passed to the
.Xr KTR_INFO 9
calls which declared the events.
.Pp
Unless
.Dv KTR_ALL
is specified in the kernel configuration, the default is to turn on logging
for all corresponding events (i.e.\& setting the sysctl to -1).
.It Va debug.ktr.*_mask
Read only sysctls (one per event) that show the
.Va debug.ktr.*_enable
values corresponding to the events.
.It Va debug.ktr.resynchronize
Resynchronize the TSC across all CPUs 10 times per second in an attempt to
reduce drift errors.
Note that this is very expensive and therefore the default is 0.
.El
.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 .