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KTR(4)		      DragonFly Kernel Interfaces Manual		KTR(4)

NAME

ktr -- kernel tracing facility

SYNOPSIS

options KTR options KTR_ENTRIES=8192 options KTR_VERBOSE=1 options KTR_ALL options KTR_ACPI_EC options KTR_CTXSW options KTR_DMCRYPT options KTR_ETHERNET options KTR_IF_BGE options KTR_IF_EM options KTR_IF_EMX options KTR_IF_POLL options KTR_IF_START options KTR_IFQ options KTR_IPIQ options KTR_KERNENTRY options KTR_MEMORY options KTR_SERIALIZER options KTR_SPIN_CONTENTION options KTR_TESTLOG options KTR_TOKENS options KTR_TSLEEP options KTR_USB_MEMORY options KTR_USCHED_BSD4 options KTR_USCHED_DFLY

DESCRIPTION

The ktr facility allows kernel events to be logged while the kernel exe- cutes so that they can be examined later when debugging. The only manda- tory option to enable ktr is options KTR. The 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 debug.ktr.entries. By default the buffer contains 2048 entries. For debugging purposes, the following ktr related kernel options exist: KTR_ALL turns on all options KTR_ACPI_EC ACPI Embedded Controller related data KTR_CTXSW context switches KTR_DMCRYPT read and write strategy paths of dm(4)'s crypt tar- get KTR_ETHERNET cost of ether_input() and ether_dispatch() KTR_IF_BGE bge(4) interrupts and sent/received packets KTR_IF_EM em(4) interrupts and sent/received packets KTR_IF_EMX emx(4) interrupts and sent/received packets KTR_IFQ classic ifq dequeue/enqueue operation KTR_IF_POLL polling(4) operation KTR_IF_START running/avoiding/scheduling ifnet.if_start KTR_IPIQ IPI related data (IPI requests, CPU synchronization etc.) KTR_KERNENTRY entry of the kernel from userland (faults, syscalls) KTR_MEMORY kmalloc(9) and kfree(9) events KTR_SERIALIZER serializer(9) related events KTR_SPIN_CONTENTION spinlock(9) contention KTR_TESTLOG IPI performance testing KTR_TOKENS LWKT token related events KTR_TSLEEP tsleep(9) and wakeup(9) KTR_USB_MEMORY USB memory allocation KTR_USCHED_BSD4 usched_bsd4 scheduling decisions KTR_USCHED_DFLY usched_dfly scheduling decisions 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 debug.ktr.verbose environment variable, or it can be examined and set after booting via the 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 KTR_VERBOSE option enables verbose mode and sets the flag to one. Examining the Events The KTR buffer can be examined with ktrdump(8), gdb(1) or from within ddb(4) via the show ktr [/v] command. This command displays the contents of the trace buffer one page at a time. At the ``--more--'' prompt, the Enter key displays one more entry and prompts again. The spacebar dis- plays 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 /v modifier is specified, then they are displayed in addi- tion to the normal output. Note that the events are displayed in reverse chronological order. That is, the most recent events are displayed first.

SYSCTL VARIABLES

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 maskbit parame- ters that were passed to the KTR_INFO(9) calls which declared the events. Unless KTR_ALL is specified in the kernel con- figuration, the default is to turn on logging for all corresponding events (i.e. setting the sysctl to -1). debug.ktr.*_mask Read only sysctls (one per event) that show the debug.ktr.*_enable values corresponding to the events. 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.

SEE ALSO

gdb(1), ddb(4), ktrdump(8), ktr(9)

HISTORY

The KTR kernel tracing facility first appeared in BSD/OS 3.0 and was imported into FreeBSD 5.0 and DragonFly 1.1. It was completely rewritten by Matthew Dillon in DragonFly 1.3. DragonFly 4.1 June 29, 2014 DragonFly 4.1