# 1 LTTng and Erlang/OTP

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1.1 Introduction

The Linux Trace Toolkit: next generation is an open source system software package for correlated tracing of the Linux kernel, user applications and libraries.

For more information, please visit http://lttng.org

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1.2 Building Erlang/OTP with LTTng support

Configure and build Erlang with LTTng support:

For LTTng to work properly with Erlang/OTP you need the following packages installed:

- LTTng-tools: a command line interface to control tracing sessions.

- LTTng-UST: user space tracing library.

On Ubuntu this can be installed via aptitude:

    $ sudo aptitude install lttng-tools liblttng-ust-dev

See Installing LTTng for more information on how to install LTTng on your system.

After LTTng is properly installed on the system Erlang/OTP can be built with LTTng support.

    $ ./configure --with-dynamic-trace=lttng
    $ make

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1.3 Dyntrace Tracepoints

All tracepoints are in the domain of org_erlang_dyntrace

All Erlang types are the string equivalent in LTTng.

process_spawn

- pid : string :: Process ID. Ex. "<0.131.0>"
- parent : string :: Process ID. Ex. "<0.131.0>"
- entry : string :: Code Location. Ex. "lists:sort/1"

Available through erlang:trace/3 with trace flag procs and {tracer,dyntrace,[]} as tracer module.

Example:

    process_spawn: { cpu_id = 3 }, { pid = "<0.131.0>", parent = "<0.130.0>", entry = "erlang:apply/2" }

process_link

- to : string :: Process ID or Port ID. Ex. "<0.131.0>"
- from : string :: Process ID or Port ID. Ex. "<0.131.0>"
- type : string :: "link" | "unlink"

Available through erlang:trace/3 with trace flag procs and {tracer,dyntrace,[]} as tracer module.

Example:

    process_link: { cpu_id = 3 }, { from = "<0.130.0>", to = "<0.131.0>", type = "link" }

process_exit

- pid : string :: Process ID. Ex. "<0.131.0>"
- reason : string :: Exit reason. Ex. "normal"

Available through erlang:trace/3 with trace flag procs and {tracer,dyntrace,[]} as tracer module.

Example:

    process_exit: { cpu_id = 3 }, { pid = "<0.130.0>", reason = "normal" }

process_register

- pid : string :: Process ID. Ex. "<0.131.0>"
- name : string :: Registered name. Ex. "logger"
- type : string :: "register" | "unregister"

Example:

    process_register: { cpu_id = 0 }, { pid = "<0.128.0>", name = "dyntrace_lttng_SUITE" type = "register" }

process_scheduled

- pid : string :: Process ID. Ex. "<0.131.0>"
- entry : string :: Code Location. Ex. "lists:sort/1"
- type : string :: "in" | "out" | "in_exiting" | "out_exiting" | "out_exited"

Available through erlang:trace/3 with trace flag running and {tracer,dyntrace,[]} as tracer module.

Example:

    process_scheduled: { cpu_id = 0 }, { pid = "<0.136.0>", entry = "erlang:apply/2", type = "in" }

port_open

- pid : string :: Process ID. Ex. "<0.131.0>"
- driver : string :: Driver name. Ex. "tcp_inet"
- port : string :: Port ID. Ex. "#Port<0.1031>"

Available through erlang:trace/3 with trace flag ports and {tracer,dyntrace,[]} as tracer module.

Example:

    port_open: { cpu_id = 5 }, { pid = "<0.131.0>", driver = "'/bin/sh -s unix:cmd'", port = "#Port<0.1887>" }

port_exit

- port : string :: Port ID. Ex. "#Port<0.1031>"
- reason : string :: Exit reason. Ex. "normal"

Available through erlang:trace/3 with trace flag ports and {tracer,dyntrace,[]} as tracer module.

Example:

    port_exit: { cpu_id = 5 }, { port = "#Port<0.1887>", reason = "normal" }

port_link

- to : string :: Process ID. Ex. "<0.131.0>"
- from : string :: Process ID. Ex. "<0.131.0>"
- type : string :: "link" | "unlink"

Available through erlang:trace/3 with trace flag ports and {tracer,dyntrace,[]} as tracer module.

Example:

    port_link: { cpu_id = 5 }, { from = "#Port<0.1887>", to = "<0.131.0>", type = "unlink" }

port_scheduled

Available through erlang:trace/3 with trace flag running and {tracer,dyntrace,[]} as tracer module.

- port : string :: Port ID. Ex. "#Port<0.1031>"
- entry : string :: Callback. Ex. "open"
- type : string :: "in" | "out" | "in_exiting" | "out_exiting" | "out_exited"

Example:

    port_scheduled: { cpu_id = 5 }, { pid = "#Port<0.1905>", entry = "close", type = "out" }

Available through erlang:trace/3 with trace flag running and {tracer,dyntrace,[]} as tracer module.

function_call

- pid : string :: Process ID. Ex. "<0.131.0>"
- entry : string :: Code Location. Ex. "lists:sort/1"
- depth : integer :: Stack depth. Ex. 0

Available through erlang:trace/3 with trace flag call and {tracer,dyntrace,[]} as tracer module.

Example:

    function_call: { cpu_id = 5 }, { pid = "<0.145.0>", entry = "dyntrace_lttng_SUITE:'-t_call/1-fun-1-'/0", depth = 0 }

function_return

- pid : string :: Process ID. Ex. "<0.131.0>"
- entry : string :: Code Location. Ex. "lists:sort/1"
- depth : integer :: Stack depth. Ex. 0

Available through erlang:trace/3 with trace flag call or return_to and {tracer,dyntrace,[]} as tracer module.

Example:

    function_return: { cpu_id = 5 }, { pid = "<0.145.0>", entry = "dyntrace_lttng_SUITE:waiter/0", depth = 0 }

function_exception

- pid : string :: Process ID. Ex. "<0.131.0>"
- entry : string :: Code Location. Ex. "lists:sort/1"
- class : string :: Error reason. Ex. "error"

Available through erlang:trace/3 with trace flag call and {tracer,dyntrace,[]} as tracer module.

Example:

    function_exception: { cpu_id = 5 }, { pid = "<0.144.0>", entry = "t:call_exc/1", class = "error" }

message_send

- from : string :: Process ID or Port ID. Ex. "<0.131.0>"
- to : string :: Process ID or Port ID. Ex. "<0.131.0>"
- message : string :: Message sent. Ex. "{<0.162.0>,ok}"

Available through erlang:trace/3 with trace flag send and {tracer,dyntrace,[]} as tracer module.

Example:

    message_send: { cpu_id = 3 }, { from = "#Port<0.1938>", to = "<0.160.0>", message = "{#Port<0.1938>,eof}" }

message_receive

- to : string :: Process ID or Port ID. Ex. "<0.131.0>"
- message : string :: Message received. Ex. "{<0.162.0>,ok}"

Available through erlang:trace/3 with trace flag 'receive' and {tracer,dyntrace,[]} as tracer module.

Example:

    message_receive: { cpu_id = 7 }, { to = "<0.167.0>", message = "{<0.165.0>,ok}" }

gc_minor_start

- pid : string :: Process ID. Ex. "<0.131.0>"
- need : integer :: Heap need. Ex. 2
- heap : integer :: Young heap word size. Ex. 233
- old_heap : integer :: Old heap word size. Ex. 233

Available through erlang:trace/3 with trace flag garbage_collection and {tracer,dyntrace,[]} as tracer module.

Example:

    gc_minor_start: { cpu_id = 0 }, { pid = "<0.172.0>", need = 0, heap = 610, old_heap = 0 }

gc_minor_end

- pid : string :: Process ID. Ex. "<0.131.0>"
- reclaimed : integer :: Heap reclaimed. Ex. 2
- heap : integer :: Young heap word size. Ex. 233
- old_heap : integer :: Old heap word size. Ex. 233

Available through erlang:trace/3 with trace flag garbage_collection and {tracer,dyntrace,[]} as tracer module.

Example:

    gc_minor_end: { cpu_id = 0 }, { pid = "<0.172.0>", reclaimed = 120, heap = 1598, old_heap = 1598 }

gc_major_start

- pid : string :: Process ID. Ex. "<0.131.0>"
- need : integer :: Heap need. Ex. 2
- heap : integer :: Young heap word size. Ex. 233
- old_heap : integer :: Old heap word size. Ex. 233

Available through erlang:trace/3 with trace flag garbage_collection and {tracer,dyntrace,[]} as tracer module.

Example:

    gc_major_start: { cpu_id = 0 }, { pid = "<0.172.0>", need = 8, heap = 2586, old_heap = 1598 }

gc_major_end

- pid : string :: Process ID. Ex. "<0.131.0>"
- reclaimed : integer :: Heap reclaimed. Ex. 2
- heap : integer :: Young heap word size. Ex. 233
- old_heap : integer :: Old heap word size. Ex. 233

Available through erlang:trace/3 with trace flag garbage_collection and {tracer,dyntrace,[]} as tracer module.

Example:

    gc_major_end: { cpu_id = 0 }, { pid = "<0.172.0>", reclaimed = 240, heap = 4185, old_heap = 0 }

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1.4 BEAM Tracepoints

All tracepoints are in the domain of org_erlang_otp

All Erlang types are the string equivalent in LTTng.

driver_init

- driver : string :: Driver name. Ex. "tcp_inet"
- major : integer :: Major version. Ex. 3
- minor : integer :: Minor version. Ex. 1
- flags : integer :: Flags. Ex. 1

Example:

    driver_init: { cpu_id = 2 }, { driver = "caller_drv", major = 3, minor = 3, flags = 1 }

driver_start

- pid : string :: Process ID. Ex. "<0.131.0>"
- driver : string :: Driver name. Ex. "tcp_inet"
- port : string :: Port ID. Ex. "#Port<0.1031>"

Example:

    driver_start: { cpu_id = 2 }, { pid = "<0.198.0>", driver = "caller_drv", port = "#Port<0.3676>" }

driver_output

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"
- bytes : integer :: Size of data returned. Ex. 82

Example:

    driver_output: { cpu_id = 2 }, { pid = "<0.198.0>", port = "#Port<0.3677>", driver = "/bin/sh -s unix:cmd", bytes = 36 }

driver_outputv

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"
- bytes : integer :: Size of data returned. Ex. 82

Example:

    driver_outputv: { cpu_id = 5 }, { pid = "<0.194.0>", port = "#Port<0.3663>", driver = "tcp_inet", bytes = 3 }

driver_ready_input

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"

Example:

    driver_ready_input: { cpu_id = 5 }, { pid = "<0.189.0>", port = "#Port<0.3637>", driver = "inet_gethost 4 " }

driver_ready_output

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"

Example:

    driver_ready_output: { cpu_id = 5 }, { pid = "<0.194.0>", port = "#Port<0.3663>", driver = "tcp_inet" }

driver_timeout

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"

Example:

    driver_timeout: { cpu_id = 5 }, { pid = "<0.196.0>", port = "#Port<0.3664>", driver = "tcp_inet" }

driver_stop_select

- driver : string :: Driver name. Ex. "tcp_inet"

Example:

    driver_stop_select: { cpu_id = 5 }, { driver = "unknown" }

driver_flush

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"

Example:

    driver_flush: { cpu_id = 7 }, { pid = "<0.204.0>", port = "#Port<0.3686>", driver = "tcp_inet" }

driver_stop

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"

Example:

    driver_stop: { cpu_id = 5 }, { pid = "[]", port = "#Port<0.3673>", driver = "tcp_inet" }

driver_process_exit

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"

driver_ready_async

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"

Example:

    driver_ready_async: { cpu_id = 3 }, { pid = "<0.181.0>", port = "#Port<0.3622>", driver = "tcp_inet" }

driver_call

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"
- command : integer :: Command integer. Ex. 1
- bytes : integer :: Size of data returned. Ex. 82

Example:

    driver_call: { cpu_id = 2 }, { pid = "<0.202.0>", port = "#Port<0.3676>", driver = "caller_drv", command = 0, bytes = 2 }

driver_control

- pid : string :: Process ID. Ex. "<0.131.0>"
- port : string :: Port ID. Ex. "#Port<0.1031>"
- driver : string :: Driver name. Ex. "tcp_inet"
- command : integer :: Command integer. Ex. 1
- bytes : integer :: Size of data returned. Ex. 82

Example:

    driver_control: { cpu_id = 3 }, { pid = "<0.32767.8191>", port = "#Port<0.0>", driver = "forker", command = 83, bytes = 32 }

carrier_create

- type : string :: Carrier type. Ex. "ets_alloc"
- instance : integer :: Allocator instance. Ex. 1
- size : integer :: Carrier size. Ex. 262144
- mbc_carriers : integer :: Number of multiblock carriers in instance. Ex. 3
- mbc_carriers_size : integer :: Total size of multiblock blocks carriers in instance. Ex. 1343488
- mbc_blocks : integer :: Number of multiblock blocks in instance. Ex. 122
- mbc_blocks_size : integer :: Total size of all multiblock blocks in instance. Ex. 285296
- sbc_carriers : integer :: Number of singleblock carriers in instance. Ex. 1
- sbc_carriers_size : integer :: Total size of singleblock blocks carriers in instance. Ex. 1343488
- sbc_blocks : integer :: Number of singleblocks in instance. Ex. 1
- sbc_blocks_size : integer :: Total size of all singleblock blocks in instance. Ex. 285296

Example:

    carrier_create: { cpu_id = 2 }, { type = "ets_alloc", instance = 7, size = 2097152, mbc_carriers = 4, mbc_carriers_size = 3440640, mbc_blocks = 526, mbc_blocks_size = 1278576, sbc_carriers = 0, sbc_carriers_size = 0, sbc_blocks = 0, sbc_blocks_size = 0 }

carrier_destroy

- type : string :: Carrier type. Ex. "ets_alloc"
- instance : integer :: Allocator instance. Ex. 1
- size : integer :: Carrier size. Ex. 262144
- mbc_carriers : integer :: Number of multiblock carriers in instance. Ex. 3
- mbc_carriers_size : integer :: Total size of multiblock blocks carriers in instance. Ex. 1343488
- mbc_blocks : integer :: Number of multiblock blocks in instance. Ex. 122
- mbc_blocks_size : integer :: Total size of all multiblock blocks in instance. Ex. 285296
- sbc_carriers : integer :: Number of singleblock carriers in instance. Ex. 1
- sbc_carriers_size : integer :: Total size of singleblock blocks carriers in instance. Ex. 1343488
- sbc_blocks : integer :: Number of singleblocks in instance. Ex. 1
- sbc_blocks_size : integer :: Total size of all singleblock blocks in instance. Ex. 285296

Example:

    carrier_destroy: { cpu_id = 6 }, { type = "ets_alloc", instance = 7, size = 262144, mbc_carriers = 3, mbc_carriers_size = 3178496, mbc_blocks = 925, mbc_blocks_size = 2305336, sbc_carriers = 0, sbc_carriers_size = 0, sbc_blocks = 0, sbc_blocks_size = 0 }

carrier_pool_put

- type : string :: Carrier type. Ex. "ets_alloc"
- instance : integer :: Allocator instance. Ex. 1
- size : integer :: Carrier size. Ex. 262144

Example:

    carrier_pool_put: { cpu_id = 3 }, { type = "ets_alloc", instance = 5, size = 1048576 }

carrier_pool_get

- type : string :: Carrier type. Ex. "ets_alloc"
- instance : integer :: Allocator instance. Ex. 1
- size : integer :: Carrier size. Ex. 262144

Example:

    carrier_pool_get: { cpu_id = 7 }, { type = "ets_alloc", instance = 4, size = 3208 }

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1.5 Example of process tracing

An example of process tracing of os_mon and friends.

Clean start of lttng in a bash shell.

    $ lttng create erlang-demo
    Spawning a session daemon
    Session erlang-demo created.
    Traces will be written in /home/egil/lttng-traces/erlang-demo-20160526-165920

Start an Erlang node with lttng enabled.

    $ erl
    Erlang/OTP 19 [erts-8.0] [source-4d7b24d] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [lttng]

    Eshell V8.0  (abort with ^G)
    1>

Load the dyntrace module.

    1> l(dyntrace).
    {module,dyntrace}

All tracepoints via dyntrace are now visible and can be listed through lttng list -u.

Enable the process_register LTTng tracepoint for Erlang.

    $ lttng enable-event -u org_erlang_dyntrace:process_register
    UST event org_erlang_dyntrace:process_register created in channel channel0

Enable process tracing for new processes and use dyntrace as tracer backend.

    2> erlang:trace(new,true,[procs,{tracer,dyntrace,[]}]).
    0

Start LTTng tracing.

    $ lttng start
    Tracing started for session erlang-demo

Start the os_mon application in Erlang.

    3> application:ensure_all_started(os_mon).
    {ok,[sasl,os_mon]}

Stop LTTng tracing and view the result.

    $ lttng stop
    Tracing stopped for session erlang-demo
    $ lttng view
    [17:20:42.561168759] (+?.?????????) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.66.0>", name = "sasl_sup", type = "register" }
    [17:20:42.561215519] (+0.000046760) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.67.0>", name = "sasl_safe_sup", type = "register" }
    [17:20:42.562149024] (+0.000933505) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.68.0>", name = "alarm_handler", type = "register" }
    [17:20:42.571035803] (+0.008886779) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.69.0>", name = "release_handler", type = "register" }
    [17:20:42.574939868] (+0.003904065) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.74.0>", name = "os_mon_sup", type = "register" }
    [17:20:42.576818712] (+0.001878844) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.75.0>", name = "disksup", type = "register" }
    [17:20:42.580032013] (+0.003213301) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.76.0>", name = "memsup", type = "register" }
    [17:20:42.583046339] (+0.003014326) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.78.0>", name = "cpu_sup", type = "register" }
    [17:20:42.586206242] (+0.003159903) elxd1168lx9 org_erlang_dyntrace:process_register: \
        { cpu_id = 5 }, { pid = "<0.82.0>", name = "timer_server", type = "register" }