15. Eventlog encodings¶
This section documents the encodings of the events emitted to GHC’s event log. These events can include information about the thread scheduling events, garbage collection statistics, profiling information, user-defined tracing events.
This section is intended for implementors of tooling which consume these events.
GHC ships with a C header file (EventlogFormat.h
) which provides symbolic
names for the event type IDs described in this file.
15.1. Event log format¶
The log format is designed to be extensible: old tools should be able to parse (but not necessarily understand all of) new versions of the format, and new tools will be able to understand old log files.
- The format is endian-independent: all values are represented in big-endian order.
- The format is extensible:
- The header describes each event type and its length. Tools that don’t recognise a particular event type can skip those events.
- There is room for extra information in the event type specification, which can be ignored by older tools.
- Events can have extra information added, but existing fields cannot be changed. Tools should ignore extra fields at the end of the event record.
The event-log stream begins with a header describing the event types present in the file. The header is followed by the event records themselves, each of which consist of a 64-bit timestamp
log : EVENT_HEADER_BEGIN
EventType*
EVENT_HEADER_END
EVENT_DATA_BEGIN
Event*
EVENT_DATA_END
EventType :
EVENT_ET_BEGIN
Word16 -- unique identifier for this event
Int16 -- >=0 size of the event in bytes (minus the header)
-- -1 variable size
Word32 -- length of the next field in bytes
Word8* -- string describing the event
Word32 -- length of the next field in bytes
Word8* -- extra info (for future extensions)
EVENT_ET_END
Event :
Word16 -- event_type
Word64 -- time (nanosecs)
[Word16] -- length of the rest (for variable-sized events only)
... extra event-specific info ...
There are two classes of event types:
- Fixed size: All event records of a fixed-sized type are of the same length, given in the header event-log header.
- Variable size: Each event record includes a length field.
15.2. Runtime system diagnostics¶
ThreadId ~ Word32
CapNo ~ Word16
CapSetId ~ Word32
15.2.1. Capability sets¶
TODO
15.2.2. Environment information¶
These events are typically produced during program startup and describe the environment which the program is being run in.
-
RTS_IDENTIFIER
¶ Tag: 29 Length: variable Field CapSetId: Capability set Field String: Runtime system name and version. Describes the name and version of the runtime system responsible for the indicated capability set.
-
PROGRAM_ARGS
¶ Tag: 30 Length: variable Field CapSetId: Capability set Field [String]: The command-line arguments passed to the program Describes the command-line used to start the program.
-
PROGRAM_ENV
¶ Tag: 31 Length: variable Field CapSetId: Capability set Field [String]: The environment variable name/value pairs. (TODO: encoding?) Describes the environment variables present in the program’s environment.
15.2.3. Thread and scheduling events¶
-
CREATE_THREAD
¶ Tag: 0 Length: fixed Field ThreadId: thread id Marks the creation of a Haskell thread.
-
RUN_THREAD
¶ Tag: 1 Length: fixed Field ThreadId: thread id The indicated thread has started running.
-
STOP_THREAD
¶ Tag: 2
Length: fixed
Field ThreadId: thread id
Field Word16: status
- 1: HeapOverflow
- 2: StackOverflow
- 3: ThreadYielding
- 4: ThreadBlocked
- 5: ThreadFinished
- 6: ForeignCall
- 7: BlockedOnMVar
- 8: BlockedOnBlackHole
- 9: BlockedOnRead
- 10: BlockedOnWrite
- 11: BlockedOnDelay
- 12: BlockedOnSTM
- 13: BlockedOnDoProc
- 16: BlockedOnMsgThrowTo
Field ThreadId: thread id of thread being blocked on (only for some status values)
The indicated thread has stopped running for the reason given by
status
.
-
THREAD_RUNNABLE
¶ Tag: 3 Length: fixed Field ThreadId: thread id The indicated thread is has been marked as ready to run.
-
MIGRATE_THREAD
¶ Tag: 4 Length: fixed Field ThreadId: thread id Field CapNo: capability The indicated thread has been migrated to a new capability.
-
THREAD_WAKEUP
¶ Tag: 8 Length: fixed Field ThreadId: thread id Field CapNo: other capability The indicated thread has been woken up on another capability.
-
THREAD_LABEL
¶ Tag: 44 Length: fixed Field ThreadId: thread id Field String: label The indicated thread has been given a label (e.g. with Control.Concurrent.setThreadLabel).
15.2.4. Garbage collector events¶
-
GC_START
¶ Tag: 9 Length: fixed A garbage collection pass has been started.
-
GC_END
¶ Tag: 10 Length: fixed A garbage collection pass has been finished.
-
REQUEST_SEQ_GC
¶ Tag: 11 Length: fixed A sequential garbage collection has been requested by a capability.
-
REQUEST_PAR_GC
¶ Tag: 12 Length: fixed A parallel garbage collection has been requested by a capability.
-
GC_IDLE
¶ Tag: 20 Length: fixed An idle-time garbage collection has been started.
-
GC_WORK
¶ Tag: 21 Length: fixed Marks the start of concurrent scavenging.
-
GC_DONE
¶ Tag: 22 Length: fixed Marks the end of concurrent scavenging.
-
GC_STATS_GHC
¶ Tag: 53 Length: fixed Field CapSetId: heap capability set Field Word16: generation of collection Field Word64: bytes copied Field Word64: bytes of slop found Field Word64: TODO Field Word64: number of parallel garbage collection threads Field Word64: maximum number of bytes copied by any single collector thread Field Word64: total bytes copied by all collector threads Report various information about the heap configuration. Typically produced during RTS initialization..
-
GC_GLOBAL_SYNC
¶ Tag: 54 Length: fixed TODO
15.2.5. Heap events and statistics¶
-
HEAP_ALLOCATED
¶ Tag: 49 Length: fixed Field CapSetId: heap capability set Field Word64: allocated bytes A new chunk of heap has been allocated by the indicated capability set.
-
HEAP_SIZE
¶ Tag: 50 Length: fixed Field CapSetId: heap capability set Field Word64: heap size in bytes Report the heap size.
-
HEAP_LIVE
¶ Tag: 51 Length: fixed Field CapSetId: heap capability set Field Word64: heap size in bytes Report the live heap size.
-
HEAP_INFO_GHC
¶ Tag: 52 Length: fixed Field CapSetId: heap capability set Field Word16: number of garbage collection generations Field Word64: maximum heap size Field Word64: allocation area size Field Word64: MBlock size Field Word64: Block size Report various information about the heap configuration. Typically produced during RTS initialization..
15.2.6. Spark events¶
-
CREATE_SPARK_THREAD
¶ Tag: 15 Length: fixed A thread has been created to perform spark evaluation.
-
SPARK_COUNTERS
¶ Tag: 34 Length: fixed A periodic reporting of various statistics of spark evaluation.
-
SPARK_CREATE
¶ Tag: 35 Length: fixed A spark has been added to the spark pool.
-
SPARK_DUD
¶ Tag: 36 Length: fixed TODO
-
SPARK_OVERFLOW
¶ Tag: 37 Length: fixed TODO
-
SPARK_RUN
¶ Tag: 38 Length: fixed Evaluation has started on a spark.
-
SPARK_STEAL
¶ Tag: 39 Length: fixed Field Word16: capability from which the spark was stolen A spark has been stolen from another capability for evaluation.
-
SPARK_FIZZLE
¶ Tag: 40 Length: fixed A spark has been GC’d before being evaluated.
-
SPARK_GC
¶ Tag: 41 Length: fixed An unevaluated spark has been garbage collected.
15.2.7. Capability events¶
-
CAP_CREATE
¶ Tag: 45 Length: fixed Field CapNo: the capability number A capability has been started.
-
CAP_DELETE
¶ Tag: 46 Length: fixed A capability has been deleted.
-
CAP_DISABLE
¶ Tag: 47 Length: fixed A capability has been disabled.
-
CAP_ENABLE
¶ Tag: 48 Length: fixed A capability has been enabled.
15.2.8. Task events¶
-
TASK_CREATE
¶ Tag: 55 Length: fixed Field TaskId: task id Field CapNo: capability number Field ThreadId: TODO Marks the creation of a task.
-
TASK_MIGRATE
¶ Tag: 56 Length: fixed Field TaskId: task id Field CapNo: old capability Field CapNo: new capability Marks the migration of a task to a new capability.
15.2.9. Tracing events¶
-
LOG_MSG
¶ Tag: 16 Length: variable Field String: The message A log message from the runtime system.
-
BLOCK_MARKER
¶ Tag: 18 Length: variable Field Word32: size Field Word64: end time in nanoseconds Field String: marker name TODO
-
USER_MSG
¶ Tag: 19 Length: variable Field String: message A user log message (from, e.g., Control.Concurrent.traceEvent).
-
USER_MARKER
¶ Tag: 58 Length: variable Field String: marker name A user marker (from Debug.Trace.traceMarker).
15.3. Heap profiler event log output¶
The heap profiler can produce output to GHC’s event log, allowing samples to be correlated with other event log events over the program’s lifecycle.
This section defines the layout of these events. The String
type below is
defined to be a UTF-8 encoded NUL-terminated string.
15.3.1. Metadata event types¶
15.3.1.1. Beginning of sample stream¶
A single fixed-width event emitted during program start-up describing the samples that follow.
-
HEAP_PROF_BEGIN
¶ Tag: 160
Length: variable
Field Word8: profile ID
Field Word64: sampling period in nanoseconds
Field Word32: sample breadown type. One of,
HEAP_PROF_BREAKDOWN_COST_CENTER
(output from-hc
)HEAP_PROF_BREAKDOWN_CLOSURE_DESCR
(output from-hd
)HEAP_PROF_BREAKDOWN_RETAINER
(output from-hr
)HEAP_PROF_BREAKDOWN_MODULE
(output from-hm
)HEAP_PROF_BREAKDOWN_TYPE_DESCR
(output from-hy
)HEAP_PROF_BREAKDOWN_BIOGRAPHY
(output from-hb
)HEAP_PROF_BREAKDOWN_CLOSURE_TYPE
(output from-hT
)
Field String: module filter
Field String: closure description filter
Field String: type description filter
Field String: cost centre filter
Field String: cost centre stack filter
Field String: retainer filter
Field String: biography filter
15.3.1.2. Cost centre definitions¶
A variable-length packet produced once for each cost centre,
-
HEAP_PROF_COST_CENTRE
¶ Tag: 161
Length: fixed
Field Word32: cost centre number
Field String: label
Field String: module
Field String: source location
Field Word8: flags:
- bit 0: is the cost-centre a CAF?
15.3.1.3. Sample event types¶
A sample (consisting of a list of break-down classes, e.g. cost centres, and heap residency sizes), is to be encoded in the body of one or more events.
We normally mark the beginning of a new sample with an EVENT_HEAP_PROF_SAMPLE_BEGIN
event,
-
HEAP_PROF_SAMPLE_BEGIN
¶ Length: fixed Field Word64: sample number Marks the beginning of a heap profile sample.
Biographical profiling samples start with the EVENT_HEAP_BIO_PROF_SAMPLE_BEGIN
event. These events also include a timestamp which indicates when the sample
was taken. This is because all these samples will appear at the end of
the eventlog due to how the biographical profiling mode works. You can
use the timestamp to reorder the samples relative to the other events.
-
HEAP_BIO_PROF_SAMPLE_BEGIN
¶ Tag: 166 Length: fixed Field Word64: sample number Field Word64: eventlog timestamp in ns
A heap residency census will follow. Since events may only be up to 2^16^ bytes
in length a single sample may need to be split among multiple
EVENT_HEAP_PROF_SAMPLE
events. The precise format of the census entries is
determined by the break-down type.
At the end of the sample period the EVENT_HEAP_PROF_SAMPLE_END
event if
emitted. This is useful to properly delimit the sampling period and to record
the total time spent profiling.
-
HEAP_PROF_SAMPLE_END
¶ Tag: 165 Length: fixed Field Word64: sample number Marks the end of a heap profile sample.
15.3.1.4. Cost-centre break-down¶
- A variable-length packet encoding a heap profile sample broken down by,
- cost-centre (
-hc
)
- cost-centre (
-
HEAP_PROF_SAMPLE_COST_CENTRE
¶ Tag: 163 Length: variable Field Word8: profile ID Field Word64: heap residency in bytes Field Word8: stack depth Field Word32[]: cost centre stack starting with inner-most (cost centre numbers)
15.4. Time profiler event log output¶
The time profiling mode enabled by -p
also emits
sample events to the eventlog. At the start of profiling the
tick interval is emitted to the eventlog and then on each tick
the current cost centre stack is emitted. Together these
enable a user to construct an approximate track of the
executation of their program.
15.5. Biographical profile sample event¶
A variable-length packet encoding a profile sample.
-
BIO_PROF_SAMPLE_BEGIN
¶ Tag: 166 TODO
15.6. Non-moving GC event output¶
These events mark various stages of the
non-moving collection
lifecycle. These are enabled
with the +RTS -lg
event-set.
-
CONC_MARK_BEGIN
¶ Tag: 200 Length: fixed Marks the beginning of marking by the concurrent collector.
-
CONC_MARK_END
¶ Tag: 201 Length: fixed Marks the end of marking by the concurrent collector.
-
CONC_SYNC_BEGIN
¶ Tag: 202 Length: fixed Marks the beginning of the concurrent garbage collector’s post-mark synchronization phase.
-
CONC_SYNC_END
¶ Tag: 203 Length: fixed Marks the end of the concurrent garbage collector’s post-mark synchronization phase.
-
CONC_SWEEP_BEGIN
¶ Tag: 204 Length: fixed Marks the beginning of the concurrent garbage collector’s sweep phase.
-
CONC_SWEEP_END
¶ Tag: 205 Length: fixed Marks the end of the concurrent garbage collector’s sweep phase.
-
CONC_UPD_REM_SET_FLUSH
¶ Tag: 206 Length: fixed Marks a capability flushing its local update remembered set accumulator.
15.6.1. Non-moving heap census¶
The non-moving heap census events (enabled with the +RTS -ln
event-set) are
intended to provide insight into fragmentation of the non-moving heap.
-
NONMOVING_HEAP_CENSUS
¶ Tag: 207 Length: fixed Field Word8: base-2 logarithm of blk_sz. Field Word32: number of active segments. Field Word32: number of filled segments. Field Word32: number of live blocks. Describes the occupancy of the blk_sz sub-heap.