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tslog.4: Document TSLOG
Based on commit messages and Colin Percival's presentation
from BSDCan 2018 [1].
[1]: https://papers.freebsd.org/2018/bsdcan/percival-Profiling_the_FreeBSD_kernel_boot.files/percival-Profiling_the_FreeBSD_kernel_boot.pdf
Reviewed by: cperciva, debdrup
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D34430
(cherry picked from commit 5675bb5829
)
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@ -562,6 +562,7 @@ MAN= aac.4 \
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ti.4 \
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timecounters.4 \
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${_tpm.4} \
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tslog.4 \
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tty.4 \
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tun.4 \
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twa.4 \
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135
share/man/man4/tslog.4
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135
share/man/man4/tslog.4
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.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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.\"
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.\" Copyright (c) 2022 Mateusz Piotrowski <0mp@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd March 4, 2022
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.Dt TSLOG 4
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.Os
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.Sh NAME
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.Nm tslog
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.Nd Boot-time event tracing facility
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.Sh SYNOPSIS
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To compile this boot-time event tracing facility into the kernel,
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place the following line in the kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "option TSLOG"
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.Ed
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.Sh DESCRIPTION
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.Nm
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is a boot-time event tracing facility.
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Its purpose is to ease diagnosing and reducing the overall
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.Fx
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boot time by generating detailed timing information.
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.Pp
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.Nm
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is able to trace the boot loader, kernel initialization, and userland processes.
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.Pp
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In userland, it records the following details for each process ID:
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.Bl -dash
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.It
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The timestamp of the
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.Xr fork 2
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which creates the given process ID and the parent process ID.
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.It
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The path passed to
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.Xr execve 2 ,
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if any.
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.It
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The first path resolved by
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.Xr namei 9 ,
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if any.
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.It
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The timestamp of the
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.Xr exit 3
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which terminates the process.
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.El
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.Sh SYSCTL VARIABLES
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The following
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.Xr sysctl 8
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variables are available:
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.Bl -tag -width indent
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.It Va debug.tslog
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Dump the
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.Nm
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buffer of recorded loader and kernel event timestamps.
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.It Va debug.tslog_user
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Dump the
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.Nm
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buffer
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of recorded userland event timestamps.
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.El
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.Sh FLAMEGRAPHS
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The
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.Nm
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buffer dumps
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can be used to generate flamegraphs of the
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.Fx
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boot process for visual analysis.
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See
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.Lk https://github.com/cperciva/freebsd-boot-profiling
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for more information.
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.Sh SEE ALSO
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.Xr dtrace 1 ,
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.Xr boottrace 4 ,
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.Xr ktr 4
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.Sh HISTORY
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.Nm
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first appeared in
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.Fx 12.0 .
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Support for tracing boot loaders and userland process
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was added in
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.Fx 14.0 .
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.Ss TSLOG vs. Boottrace
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.Nm
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is oriented towards system developers while
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.Xr boottrace 4
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is meant to be easy to use by system administrators.
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Both faciliities provide an overview of timing and resource usage of the boot
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process.
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.Ss TSLOG vs. DTrace
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.Xr dtrace 1
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is not always the right tool for profiling early kernel initialization.
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The reason is it requires some kernel subroutines
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which are not yet available early in the boot process, e.g.:
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traps, memory allocation, or thread schedulling.
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.Nm
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depends on fewer kernel subroutines than
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.Xr dtrace 1
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and because of that can trace early kernel initialization.
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.Ss TSLOG vs. KTR
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.Xr ktr 4
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has a couple of limitations which prevent it from
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being able to run at the start of the boot process.
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In contrast,
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.Nm
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is designed for logging timestamped events for boot
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profiling.
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.Sh AUTHORS
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.An -nosplit
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.Nm
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was written by
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.An Colin Percival Aq Mt cperciva@FreeBSD.org .
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.Pp
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This manual page was written by
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.An Mateusz Piotrowski Aq Mt 0mp@FreeBSD.org .
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