File:  [NetBSD Developer Wiki] / wikisrc / tutorials / how_to_enable_and_run_dtrace.mdwn
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Wed Mar 22 15:33:08 2017 UTC (3 years, 3 months ago) by sevan
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List earm* rather than specific boards in evbarm port.
Add more providers to the list.
Note the INSECURE option is not mandatory and explain why it might be desired.
MKDTRACE & MKCTF build options are handled automatically now, direct reader to where that's controlled if the list needs to be extended.
Direct reader to use modules.conf and how they can find which modules are available on their system.
Replace instructions for creating a device node manually with a note that it is created automatically
Remove whitespace.

DTrace is a Dynamic Tracing framework developed by Sun and ported to NetBSD. It enables extensive instrumentation of the kernel and user space. See the [DTrace Community Page]( for more information. Also see [DTrace Introduction]( 

# Current status

## Supported platforms

DTrace is a work-in-progress effort and it is for x86 systems and some arm boards.

* i386 and amd64
* earm* (evbarm and armv4 based ports (armv4 side requires further testing but system is built with CTF)

## Supported providers

* SDT: Statically Defined Tracing
* FBT: Function Boundary Tracing
* Lockstat: Kernel Lock Statistics
* Profile: Time based interrupt event source for Profiling
* Syscall: System Calls
* Syscall Linux (32bit & 64 bit): System calls via the Linux binary emulation layer

## TODO for netbsd-7

* Measure effect of `options KDTRACE_HOOKS` on system performance.
* Determine whether the profile module works and list it here.
* Integrate [[riz|users/riz]]'s syscall provider patch.

## TODO for netbsd-6

Need to identify changes to pull up to netbsd-6 and pull them up.

* Profile provider.

# How to use

##  Building DTrace 

You need the following options in your kernel: 
    options         KDTRACE_HOOKS   # kernel DTrace hooks
    options         MODULAR

    options         INSECURE   # permit modules to loaded from user space once system has gone multiuser and securelevel has been raised.

A Distribution needs to be built with the options `MKDTRACE=yes` and `MKCTF=yes`, this is taken care of automatically and doesn't need to be specified manually. The list of platforms it is applied to automatically is set in `src/share/mk/`

Set the system to load the solaris and dtrace related modules in `/etc/modules.conf`, for a list of available modules, see `/stand/$MACHINE/$VERSION/modules/`
A `dtrace` device node is created automatically in `/dev/dtrace` when the modules are loaded into place.
List the dtrace probes 
    dtrace -l
       ID   PROVIDER            MODULE                          FUNCTION NAME
        1     dtrace                                                     BEGIN
        2     dtrace                                                     END
        3     dtrace                                                     ERROR
        4        fbt            netbsd             AcpiAcquireGlobalLock entry
        5        fbt            netbsd             AcpiAcquireGlobalLock return
        6        fbt            netbsd             AcpiAllocateRootTable entry
        7        fbt            netbsd                    AcpiAttachData entry
    29129        fbt           solaris                   zfs_vop_getattr entry 
    29130        fbt           solaris                   zfs_vop_getattr return
    29131       proc                                                     create
    29132       proc                                                     exec 
    29140       proc                                                     lwp_start
    29141       proc                                                     lwp_exit

##  Running hello world 

Put the following into the file hello.d:
        trace("Hello world");

Run the hello world script: 
    dtrace -s hello.d
    dtrace: script './hello.d' matched 1 probe
    CPU     ID                    FUNCTION:NAME
      0      1                           :BEGIN   Hello world

A more complex example that traces the execution of a sleep operation
in the kernel. Put it in sleep.d:
    #pragma D option flowindent
    /execname == "sleep" && guard++ == 0/
            self->traceme = 1;
            printf("fd: %d", arg0);
    fbt::syscall:entry /self->traceme/ {}
            self->traceme = 0;

Start the script running (dtrace -s sleep.d) and then execute a "sleep 2" in another shell. 

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