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Wed Mar 22 15:43:09 2017 UTC (18 months ago) by sevan
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Link to Brendan Gregg's DTrace one lines & FreeBSD articles.

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](, Brendan Gregg's [DTrace one liners]( and his notes for [DTrace on FreeBSD](

# 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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