| Commit message (Collapse) | Author | Age | Files | Lines |
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Previously no attempt was made to avoid multiple threads writing their
capability-local eventlog buffers to the eventlog writer simultaneously.
This could result in multiple eventlog streams being interleaved. Fix
this by documenting that the EventLogWriter's write() and flush()
functions may be called reentrantly and fix the default writer to
protect its FILE* by a mutex.
Fixes #18210.
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This exposes a set of interfaces from the GHC API for configuring
EventLogWriters. These can be used by consumers like
[ghc-eventlog-socket](https://github.com/bgamari/ghc-eventlog-socket).
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This introduces a concurrent mark & sweep garbage collector to manage the old
generation. The concurrent nature of this collector typically results in
significantly reduced maximum and mean pause times in applications with large
working sets.
Due to the large and intricate nature of the change I have opted to
preserve the fully-buildable history, including merge commits, which is
described in the "Branch overview" section below.
Collector design
================
The full design of the collector implemented here is described in detail
in a technical note
> B. Gamari. "A Concurrent Garbage Collector For the Glasgow Haskell
> Compiler" (2018)
This document can be requested from @bgamari.
The basic heap structure used in this design is heavily inspired by
> K. Ueno & A. Ohori. "A fully concurrent garbage collector for
> functional programs on multicore processors." /ACM SIGPLAN Notices/
> Vol. 51. No. 9 (presented at ICFP 2016)
This design is intended to allow both marking and sweeping
concurrent to execution of a multi-core mutator. Unlike the Ueno design,
which requires no global synchronization pauses, the collector
introduced here requires a stop-the-world pause at the beginning and end
of the mark phase.
To avoid heap fragmentation, the allocator consists of a number of
fixed-size /sub-allocators/. Each of these sub-allocators allocators into
its own set of /segments/, themselves allocated from the block
allocator. Each segment is broken into a set of fixed-size allocation
blocks (which back allocations) in addition to a bitmap (used to track
the liveness of blocks) and some additional metadata (used also used
to track liveness).
This heap structure enables collection via mark-and-sweep, which can be
performed concurrently via a snapshot-at-the-beginning scheme (although
concurrent collection is not implemented in this patch).
Implementation structure
========================
The majority of the collector is implemented in a handful of files:
* `rts/Nonmoving.c` is the heart of the beast. It implements the entry-point
to the nonmoving collector (`nonmoving_collect`), as well as the allocator
(`nonmoving_allocate`) and a number of utilities for manipulating the heap.
* `rts/NonmovingMark.c` implements the mark queue functionality, update
remembered set, and mark loop.
* `rts/NonmovingSweep.c` implements the sweep loop.
* `rts/NonmovingScav.c` implements the logic necessary to scavenge the
nonmoving heap.
Branch overview
===============
```
* wip/gc/opt-pause:
| A variety of small optimisations to further reduce pause times.
|
* wip/gc/compact-nfdata:
| Introduce support for compact regions into the non-moving
|\ collector
| \
| \
| | * wip/gc/segment-header-to-bdescr:
| | | Another optimization that we are considering, pushing
| | | some segment metadata into the segment descriptor for
| | | the sake of locality during mark
| | |
| * | wip/gc/shortcutting:
| | | Support for indirection shortcutting and the selector optimization
| | | in the non-moving heap.
| | |
* | | wip/gc/docs:
| |/ Work on implementation documentation.
| /
|/
* wip/gc/everything:
| A roll-up of everything below.
|\
| \
| |\
| | \
| | * wip/gc/optimize:
| | | A variety of optimizations, primarily to the mark loop.
| | | Some of these are microoptimizations but a few are quite
| | | significant. In particular, the prefetch patches have
| | | produced a nontrivial improvement in mark performance.
| | |
| | * wip/gc/aging:
| | | Enable support for aging in major collections.
| | |
| * | wip/gc/test:
| | | Fix up the testsuite to more or less pass.
| | |
* | | wip/gc/instrumentation:
| | | A variety of runtime instrumentation including statistics
| | / support, the nonmoving census, and eventlog support.
| |/
| /
|/
* wip/gc/nonmoving-concurrent:
| The concurrent write barriers.
|
* wip/gc/nonmoving-nonconcurrent:
| The nonmoving collector without the write barriers necessary
| for concurrent collection.
|
* wip/gc/preparation:
| A merge of the various preparatory patches that aren't directly
| implementing the GC.
|
|
* GHC HEAD
.
.
.
```
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This introduces a few events to mark key points in the nonmoving
garbage collection cycle. These include:
* `EVENT_CONC_MARK_BEGIN`, denoting the beginning of a round of
marking. This may happen more than once in a single major collection
since we the major collector iterates until it hits a fixed point.
* `EVENT_CONC_MARK_END`, denoting the end of a round of marking.
* `EVENT_CONC_SYNC_BEGIN`, denoting the beginning of the post-mark
synchronization phase
* `EVENT_CONC_UPD_REM_SET_FLUSH`, indicating that a capability has
flushed its update remembered set.
* `EVENT_CONC_SYNC_END`, denoting that all mutators have flushed their
update remembered sets.
* `EVENT_CONC_SWEEP_BEGIN`, denoting the beginning of the sweep portion
of the major collection.
* `EVENT_CONC_SWEEP_END`, denoting the end of the sweep portion of the
major collection.
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|/
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With this change it is possible to reconstruct the timing portion of a
`.prof` file after the fact. By logging the stacks at each time point
a more precise executation trace of the program can be observed rather
than all identical cost centres being identified in the report.
There are two new events:
1. `EVENT_PROF_BEGIN` - emitted at the start of profiling to communicate
the tick interval
2. `EVENT_PROF_SAMPLE_COST_CENTRE` - emitted on each tick to communicate the
current call stack.
Fixes #17322
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This patch adds a new eventlog event which indicates the start of
a biographical profiler sample. These are different to normal events as
they also include the timestamp of when the census took place. This is
because the LDV profiler only emits samples at the end of the run.
Now all the different profiling modes emit consumable events to the
eventlog.
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Previously there were numerous places in the RTS where we would fopen
with the "w" flag string. This is wrong as it will not truncate the
file. Consequently if we write less data than the previous length of the
file we will leave garbage at its end.
Fixes #16993.
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Previously these two orthogonal concerns were both implemented in
postHeaderEvents which made it difficult to send header events after RTS
initialization.
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This allows a user to observe how long a sampling period lasts so that
the time taken can be removed from the profiling output.
Fixes #16697
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This introduces the `+RTS -ol` flag, which allows user to specify the
destination file for eventlog output.
Test Plan: Validate with included test
Reviewers: simonmar, erikd
Reviewed By: simonmar
Subscribers: rwbarton, carter
Differential Revision: https://phabricator.haskell.org/D5293
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This adds a new primop called traceBinaryEvent# that takes the length
of binary data and a pointer to the data, then emits it to the eventlog.
There is some example code that uses this primop and the new event:
* [traceBinaryEventIO][1] that calls `traceBinaryEvent#`
* [A patch to ghc-events][2] that parses the new `EVENT_USER_BINARY_MSG`
There's no corresponding issue on Trac but it was discussed at
ghc-devs [3].
[1] https://github.com/maoe/ghc-trace-events/blob
/fb226011ef1f85a97b4da7cc9d5f98f9fe6316ae/src/Debug/Trace/Binary.hs#L29)
[2] https://github.com/maoe/ghc-events/commit
/239ca77c24d18cdd10d6d85a0aef98e4a7c56ae6)
[3] https://mail.haskell.org/pipermail/ghc-devs/2018-May/015791.html
Reviewers: bgamari, erikd, simonmar
Reviewed By: bgamari
Subscribers: rwbarton, thomie, carter
Differential Revision: https://phabricator.haskell.org/D5007
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Summary:
This shims out fopen and sopen so that they use modern APIs under the hood
along with namespaced paths.
This lifts the MAX_PATH restrictions from Haskell programs and makes the new
limit ~32k.
There are only some slight caveats that have been documented.
Some utilities have not been upgraded such as lndir, since all these things are
different cabal packages I have been forced to copy the source in different places
which is less than ideal. But it's the only way to keep sdist working.
Test Plan: ./validate
Reviewers: hvr, bgamari, erikd, simonmar
Reviewed By: bgamari
Subscribers: rwbarton, thomie, carter
GHC Trac Issues: #10822
Differential Revision: https://phabricator.haskell.org/D4416
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Test Plan: Build, program with `-eventlog`, try running with `+RTS -h`
Reviewers: austin, erikd, simonmar
Subscribers: rwbarton, thomie
GHC Trac Issues: #14096
Differential Revision: https://phabricator.haskell.org/D3922
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Reviewers: austin, erikd, simonmar
Subscribers: rwbarton, thomie
GHC Trac Issues: #14096
Differential Revision: https://phabricator.haskell.org/D3923
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An additional stat is tracked per gc: par_balanced_copied This is the
the number of bytes copied by each gc thread under the balanced lmit,
which is simply (copied_bytes / num_gc_threads). The stat is added to
all the appropriate GC structures, so is visible in the eventlog and in
GHC.Stats.
A note is added explaining how work balance is computed.
Remove some end of line whitespace
Test Plan:
./validate
experiment with the program attached to the ticket
examine code changes carefully
Reviewers: simonmar, austin, hvr, bgamari, erikd
Reviewed By: simonmar
Subscribers: Phyx, rwbarton, thomie
GHC Trac Issues: #13830
Differential Revision: https://phabricator.haskell.org/D3658
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Our new CPP linter enforces this.
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This both says what we mean and silences a bunch of spurious CPP linting
warnings. This pragma is supported by all CPP implementations which we
support.
Reviewers: austin, erikd, simonmar, hvr
Reviewed By: simonmar
Subscribers: rwbarton, thomie
Differential Revision: https://phabricator.haskell.org/D3482
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Currently eventlog data is always written to a file `progname.eventlog`.
This patch introduces the `flushEventLog` field in `RtsConfig` which
allows to customize the writing of eventlog data.
One possible scenario is the ongoing live-profile-monitor effort by
@NCrashed which slurps all eventlog data through `fluchEventLog`.
`flushEventLog` takes a buffer with eventlog data and its size and
returns `false` (0) in case eventlog data could not be procesed.
Reviewers: simonmar, austin, erikd, bgamari
Reviewed By: simonmar, bgamari
Subscribers: qnikst, thomie, NCrashed
Differential Revision: https://phabricator.haskell.org/D2934
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Test Plan: Try it
Reviewers: hvr, simonmar, austin, erikd
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1722
GHC Trac Issues: #11094
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Summary:
The aim here is to reduce the number of remote memory accesses on
systems with a NUMA memory architecture, typically multi-socket servers.
Linux provides a NUMA API for doing two things:
* Allocating memory local to a particular node
* Binding a thread to a particular node
When given the +RTS --numa flag, the runtime will
* Determine the number of NUMA nodes (N) by querying the OS
* Assign capabilities to nodes, so cap C is on node C%N
* Bind worker threads on a capability to the correct node
* Keep a separate free lists in the block layer for each node
* Allocate the nursery for a capability from node-local memory
* Allocate blocks in the GC from node-local memory
For example, using nofib/parallel/queens on a 24-core 2-socket machine:
```
$ ./Main 15 +RTS -N24 -s -A64m
Total time 173.960s ( 7.467s elapsed)
$ ./Main 15 +RTS -N24 -s -A64m --numa
Total time 150.836s ( 6.423s elapsed)
```
The biggest win here is expected to be allocating from node-local
memory, so that means programs using a large -A value (as here).
According to perf, on this program the number of remote memory accesses
were reduced by more than 50% by using `--numa`.
Test Plan:
* validate
* There's a new flag --debug-numa=<n> that pretends to do NUMA without
actually making the OS calls, which is useful for testing the code
on non-NUMA systems.
* TODO: I need to add some unit tests
Reviewers: erikd, austin, rwbarton, ezyang, bgamari, hvr, niteria
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2199
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The `nat` type was an alias for `unsigned int` with a comment saying
it was at least 32 bits. We keep the typedef in case client code is
using it but mark it as deprecated.
Test Plan: Validated on Linux, OS X and Windows
Reviewers: simonmar, austin, thomie, hvr, bgamari, hsyl20
Differential Revision: https://phabricator.haskell.org/D2166
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Previously the eventlog flush code would fail if `fwrite` wrote less
than the requested amount. Like all Unix stream I/O operations, however,
`fwrite` isn't guaranteed to write the entire buffer. Here we loop as
long as `fwrite` succeeds in writing anything.
Fixes #11041.
Test Plan: Validate with eventlog
Reviewers: austin, simonmar
Reviewed By: simonmar
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1415
GHC Trac Issues: #11041
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This has been unnecessary for quite some time due to the create/delete
capability events.
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Summary:
Don't call postLogMsg to post a user msg, because it truncates messages to
512 bytes.
Rename traceCap_stderr and trace_stderr to vtraceCap_stderr and trace_stderr,
to signal that they take a va_list (similar to vdebugBelch vs debugBelch).
See #3874 for the original reason behind traceFormatUserMsg.
See the commit msg in #9395 (d360d440) for a discussion about using
null-terminated strings vs strings with an explicit length.
Test Plan:
Run `cabal install ghc-events` and inspect the result of `ghc-events show` on
an eventlog file created with `ghc -eventlog Test.hs` and `./Test +RTS -l`,
where Test.hs contains:
```
import Debug.Trace
main = traceEvent (replicate 510 'a' ++ "bcd") $ return ()
```
Depends on D655.
Reviewers: austin
Reviewed By: austin
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D656
GHC Trac Issues: #8309
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Event log had inconcistent support for increacing capabilies
number, as header were not inserted in capability buffer. It
resulted in a ghc-events crash (see #9384). This commit
fixes this issue by inserting required header when number
of capabilies grows.
Reviewers: simonmar, Mikolaj, trofi, austin
Reviewed By: Mikolaj, trofi, austin
Subscribers: carter, thomie
Differential Revision: https://phabricator.haskell.org/D592
GHC Trac Issues: #9384
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This reverts commit 39b5c1cbd8950755de400933cecca7b8deb4ffcd.
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This will hopefully help ensure some basic consistency in the forward by
overriding buffer variables. In particular, it sets the wrap length, the
offset to 4, and turns off tabs.
Signed-off-by: Austin Seipp <austin@well-typed.com>
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Signed-off-by: Austin Seipp <austin@well-typed.com>
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The TL;DR is that by adding this, we can distinguish GHC 7.8.3 from
7.8.2, which had a buggy implementation. See the ticket for details.
Signed-off-by: Austin Seipp <austin@well-typed.com>
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After a toolchain update, Clang is no longer appreciative of the fact
these are unused, thanks to -Werror during validate.
Signed-off-by: Austin Seipp <austin@well-typed.com>
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In time-based profiling visualisations (e.g. heap profiles and ThreadScope)
it would be useful to be able to mark particular points in the execution and
have those points in time marked in the visualisation.
The traceMarker# primop currently emits an event into the eventlog. In
principle it could be extended to do something in the heap profiling too.
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lnat was originally "long unsigned int" but we were using it when we
wanted a 64-bit type on a 64-bit machine. This broke on Windows x64,
where long == int == 32 bits. Using types of unspecified size is bad,
but what we really wanted was a type with N bits on an N-bit machine.
StgWord is exactly that.
lnat was mentioned in some APIs that clients might be using
(e.g. StackOverflowHook()), so we leave it defined but with a comment
to say that it's deprecated.
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Based on initial patches by Mikolaj Konarski <mikolaj@well-typed.com>
These new eventlog events are to let profiling tools keep track of all
the OS threads that belong to an RTS capability at any moment in time.
In the RTS, OS threads correspond to the Task abstraction, so that is
what we track. There are events for tasks being created, migrated
between capabilities and deleted. In particular the task creation event
also records the kernel thread id which lets us match up the OS thread
with data collected by others tools (in the initial use case with
Linux's perf tool, but in principle also with DTrace).
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I've assumed that the definition type is right.
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Quoting design rationale by dcoutts: The event indicates that we're doing
a stop-the-world GC and all other HECs should be between their GC_START
and GC_END events at that moment. We don't want to use GC_STATS_GHC
for that, because GC_STATS_GHC is for extra GHC-specific info,
not something we have to rely on to be able to match the GC pauses
across HECs to a particular global GC.
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There was a discrepancy between GC times reported in +RTS -s
and the timestamps of GC_START and GC_END events on the cap,
on which +RTS -s stats for the given GC are based.
This is fixed by posting the events with exactly the same timestamp
as generated for the stat calculation. The calls posting the events
are moved too, so that the events are emitted close to the time instant
they claim to be emitted at. The GC_STATS_GHC was moved, too, ensuring
it's emitted before the moved GC_END on all caps, which simplifies tools code.
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The EventLogFormat.h described the spark counter fields in a different
order to that which ghc emits (the GC'd and fizzled fields were
reversed). At this stage it is easier to fix the ghc-events lib and
to have ghc continue to emit them in the current order.
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They cover much the same info as is available via the GHC.Stats module
or via the '+RTS -s' textual output, but via the eventlog and with a
better sampling frequency.
We have three new generic heap info events and two very GHC-specific
ones. (The hope is the general ones are usable by other implementations
that use the same eventlog system, or indeed not so sensitive to changes
in GHC itself.)
The general ones are:
* total heap mem allocated since prog start, on a per-HEC basis
* current size of the heap (MBlocks reserved from OS for the heap)
* current size of live data in the heap
Currently these are all emitted by GHC at GC time (live data only at
major GC).
The GHC specific ones are:
* an event giving various static heap paramaters:
* number of generations (usually 2)
* max size if any
* nursary size
* MBlock and block sizes
* a event emitted on each GC containing:
* GC generation (usually just 0,1)
* total bytes copied
* bytes lost to heap slop and fragmentation
* the number of threads in the parallel GC (1 for serial)
* the maximum number of bytes copied by any par GC thread
* the total number of bytes copied by all par GC threads
(these last three can be used to calculate an estimate of the
work balance in parallel GCs)
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Now that we can adjust the number of capabilities on the fly, we need
this reflected in the eventlog. Previously the eventlog had a single
startup event that declared a static number of capabilities. Obviously
that's no good anymore.
For compatability we're keeping the EVENT_STARTUP but adding new
EVENT_CAP_CREATE/DELETE. The EVENT_CAP_DELETE is actually just the old
EVENT_SHUTDOWN but renamed and extended (using the existing mechanism
to extend eventlog events in a compatible way). So we now emit both
EVENT_STARTUP and EVENT_CAP_CREATE. One day we will drop EVENT_STARTUP.
Since reducing the number of capabilities at runtime does not really
delete them, it just disables them, then we also have new events for
disable/enable.
The old EVENT_SHUTDOWN was in the scheduler class of events. The new
EVENT_CAP_* events are in the unconditional class, along with the
EVENT_CAPSET_* ones. Knowing when capabilities are created and deleted
is crucial to making sense of eventlogs, you always want those events.
In any case, they're extremely low volume.
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At present the number of capabilities can only be *increased*, not
decreased. The latter presents a few more challenges!
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Terminology cleanup: the type "Ticks" has been renamed "Time", which
is an StgWord64 in units of TIME_RESOLUTION (currently nanoseconds).
The terminology "tick" is now used consistently to mean the interval
between timer signals.
The ticker now always ticks in realtime (actually CLOCK_MONOTONIC if
we have it). Before it used CPU time in the non-threaded RTS and
realtime in the threaded RTS, but I've discovered that the CPU timer
has terrible resolution (at least on Linux) and isn't much use for
profiling. So now we always use realtime. This should also fix
The default tick interval is now 10ms, except when profiling where we
drop it to 1ms. This gives more accurate profiles without affecting
runtime too much (<1%).
Lots of cleanups - the resolution of Time is now in one place
only (Rts.h) rather than having calculations that depend on the
resolution scattered all over the RTS. I hope I found them all.
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Fixes ticket #5472
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