1.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org> 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $ 26.\" 27.Dd June 29, 2014 28.Dt KTR 4 29.Os 30.Sh NAME 31.Nm ktr 32.Nd kernel tracing facility 33.Sh SYNOPSIS 34.Cd options KTR 35.Cd options KTR_ENTRIES=8192 36.Cd options KTR_VERBOSE=1 37.Cd options KTR_ALL 38.Cd options KTR_ACPI_EC 39.Cd options KTR_CTXSW 40.Cd options KTR_DMCRYPT 41.Cd options KTR_ETHERNET 42.\".Cd options KTR_HAMMER 43.Cd options KTR_IF_BGE 44.Cd options KTR_IF_EM 45.Cd options KTR_IF_EMX 46.Cd options KTR_IF_POLL 47.Cd options KTR_IF_START 48.Cd options KTR_IFQ 49.Cd options KTR_IPIQ 50.Cd options KTR_KERNENTRY 51.Cd options KTR_MEMORY 52.Cd options KTR_SERIALIZER 53.Cd options KTR_SPIN_CONTENTION 54.\".Cd options KTR_TCP 55.Cd options KTR_TESTLOG 56.Cd options KTR_TOKENS 57.Cd options KTR_TSLEEP 58.Cd options KTR_USCHED_BSD4 59.Cd options KTR_USCHED_DFLY 60.Sh DESCRIPTION 61The 62.Nm 63facility allows kernel events to be logged while the kernel executes so that 64they can be examined later when debugging. 65The only mandatory option to enable 66.Nm 67is 68.Cd options KTR . 69.Pp 70The 71.Dv KTR_ENTRIES 72option sets the size of the buffer of events. 73It must be a power of two. 74The size of the buffer in the currently running kernel can be found via the 75read-only sysctl 76.Va debug.ktr.entries . 77By default the buffer contains 2048 entries. 78.Pp 79For debugging purposes, the following 80.Nm 81related kernel options exist: 82.Bl -tag -width ".Dv KTR_SPIN_CONTENTION" 83.It Dv KTR_ALL 84turns on all options 85.It Dv KTR_ACPI_EC 86ACPI Embedded Controller related data 87.It Dv KTR_CTXSW 88context switches 89.It Dv KTR_DMCRYPT 90read and write strategy paths of 91.Xr dm 4 Ap s 92.Pa crypt 93target 94.It Dv KTR_ETHERNET 95cost of 96.Fn ether_input 97and 98.Fn ether_dispatch 99.It Dv KTR_IF_BGE 100.Xr bge 4 101interrupts and sent/received packets 102.It Dv KTR_IF_EM 103.Xr em 4 104interrupts and sent/received packets 105.It Dv KTR_IF_EMX 106.Xr emx 4 107interrupts and sent/received packets 108.It Dv KTR_IFQ 109classic ifq dequeue/enqueue operation 110.It Dv KTR_IF_POLL 111.Xr polling 4 112operation 113.It Dv KTR_IF_START 114running/avoiding/scheduling ifnet.if_start 115.It Dv KTR_IPIQ 116IPI related data (IPI requests, CPU synchronization etc.) 117.It Dv KTR_KERNENTRY 118entry of the kernel from userland (faults, syscalls) 119.It Dv KTR_MEMORY 120.Xr kmalloc 9 121and 122.Xr kfree 9 123events 124.It Dv KTR_SERIALIZER 125.Xr serializer 9 126related events 127.It Dv KTR_SPIN_CONTENTION 128.Xr spinlock 9 129contention 130.It Dv KTR_TESTLOG 131IPI performance testing 132.It Dv KTR_TOKENS 133LWKT token related events 134.It Dv KTR_TSLEEP 135.Xr tsleep 9 136and 137.Xr wakeup 9 138.It Dv KTR_USCHED_BSD4 139usched_bsd4 scheduling decisions 140.It Dv KTR_USCHED_DFLY 141usched_dfly scheduling decisions 142.El 143.Ss Verbose Mode 144By default, events are only logged to the internal buffer for examination 145later, but if the verbose flag is set then they are dumped to the kernel 146console as well. 147This flag can also be set from the loader via the 148.Va debug.ktr.verbose 149environment variable, or it can be examined and set after booting via the 150.Va debug.ktr.verbose 151sysctl. 152If the flag is set to zero, which is the default, then verbose output is 153disabled. 154If the flag is set to one, then the contents of the log message and the CPU 155number are printed to the kernel console. 156If the flag is greater than one, then the filename and line number of the 157event are output to the console in addition to the log message and the CPU 158number. 159The 160.Dv KTR_VERBOSE 161option enables verbose mode and sets the flag to one. 162.Ss Examining the Events 163The KTR buffer can be examined with 164.Xr ktrdump 8 , 165.Xr gdb 1 166or from within 167.Xr ddb 4 168via the 169.Ic show ktr Op Cm /v 170command. 171This command displays the contents of the trace buffer one page at a time. 172At the 173.Dq Li --more-- 174prompt, the Enter key displays one more entry and prompts again. 175The spacebar displays another page of entries. 176Any other key quits. 177By default the timestamp, filename, and line number are not displayed with 178each log entry. 179If the 180.Cm /v 181modifier is specified, then they are displayed in addition to the normal 182output. 183Note that the events are displayed in reverse chronological order. 184That is, the most recent events are displayed first. 185.Sh SYSCTL VARIABLES 186.Bl -tag -width ".Va debug.ktr.resynchronize" 187.It Va debug.ktr.*_enable 188A 32 bit mask used to control event logging. 189Each bit corresponds to one or more events depending on the values of the 190.Fa maskbit 191parameters that were passed to the 192.Xr KTR_INFO 9 193calls which declared the events. 194.Pp 195Unless 196.Dv KTR_ALL 197is specified in the kernel configuration, the default is to turn on logging 198for all corresponding events (i.e.\& setting the sysctl to -1). 199.It Va debug.ktr.*_mask 200Read only sysctls (one per event) that show the 201.Va debug.ktr.*_enable 202values corresponding to the events. 203.It Va debug.ktr.resynchronize 204Resynchronize the TSC across all CPUs 10 times per second in an attempt to 205reduce drift errors. 206Note that this is very expensive and therefore the default is 0. 207.El 208.Sh SEE ALSO 209.Xr gdb 1 , 210.Xr ddb 4 , 211.Xr ktrdump 8 , 212.Xr ktr 9 213.Sh HISTORY 214The KTR kernel tracing facility first appeared in 215.Bsx 3.0 216and was imported into 217.Fx 5.0 218and 219.Dx 1.1 . 220It was completely rewritten by Matthew Dillon in 221.Dx 1.3 . 222