![]() https://dart-review.googlesource.com/c/sdk/+/287660 implements it. I want to fix pre-existing violations before enabling. Bug: https://github.com/dart-lang/sdk/issues/34978 Change-Id: Ie7731162c643018a2312b265f444bc00534c0a51 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/287664 Reviewed-by: Leon Senft <leonsenft@google.com> Commit-Queue: Konstantin Shcheglov <scheglov@google.com> Reviewed-by: Ben Konyi <bkonyi@google.com> Reviewed-by: Brian Wilkerson <brianwilkerson@google.com> Reviewed-by: Johnni Winther <johnniwinther@google.com> |
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bin | ||
lib | ||
test | ||
.gitignore | ||
analysis_options.yaml | ||
AUTHORS | ||
CHANGELOG.md | ||
LICENSE | ||
OWNERS | ||
pubspec.yaml | ||
README.md |
This package provides libraries and a utility for analysing the size and
contents of Dart VM AOT snapshots based on the output of
--print-instructions-sizes-to
, --write-v8-snapshot-profile-to
and
--trace-precompiler-to
VM flags.
AOT Snapshot Basics
Dart VM AOT snapshot is simply a serialized representation of the Dart VM
heap graph. It consists of two parts: data (e.g. strings, const
instances,
objects representing classes, libraries, functions and runtime metadata) and
executable code (machine code generated from Dart sources). Some nodes in this
graph have clean and direct relationship to the original program (e.g. objects
representing libraries, classes, functions), while other nodes don't. Bitwise
equivalent objects can be deduplicated and shared (e.g. two functions with the
same body will end up using the same machine code object). This makes
impossible to attribute of every single byte from the snapshot to a particular
place in the program with a 100% accuracy.
--print-instructions-sizes-to
attributes executable code from the snapshot to a particular Dart function (or internal stub) from which this code originated (ignoring deduplication). Executable code usually constitutes around half of the snapshot, those this varies depending on the application.--write-v8-snapshot-profile-to
is a graph representation of the snapshot, it attributes bytes written into a snapshot to a node in the heap graph. This format covers both data and code sections of the snapshot.--trace-precompiler-to
gives information about dependencies between compiled functions, allowing to determine why certain function was pulled into the snapshot.
Passing flags to the AOT compiler
Both in dart2native
and Flutter you can use --extra-gen-snapshot-options
to
pass flags to the AOT compiler:
$ flutter build aot --release --extra-gen-snapshot-options=--write-v8-snapshot-profile-to=profile.json
$ dart2native --extra-gen-snapshot-options=--write-v8-snapshot-profile-to=profile.json -o binary input.dart
Similarly with --print-instructions-sizes-to
.
If you are working on the Dart SDK you can use the pkg/vm/tool/precompiler2
script, in which case you can just pass these flags directly:
$ pkg/vm/tool/precompiler2 --write-v8-snapshot-profile-to=profile.json input.dart binary
CLI
The command line interface to the tools in this package is provided by a single
entry point bin/analyse.dart
. It consumes output of
--print-instructions-sizes-to
and --write-v8-snapshot-profile-to
flags and
presents it in different human readable ways.
This script can be installed globally as snapshot_analysis
using
$ pub global activate vm_snapshot_analysis
snapshot_analysis
supports the following subcommands:
summary
$ snapshot_analysis summary [-b granularity] [-w filter] <input-profile.json>
This command shows breakdown of snapshot bytes at the given granularity
(e.g.
method
, class
, library
or package
), filtered by the given substring
filter
.
For example, here is a output showing how many bytes from a snapshot
can be attributed to classes in the dart:core
library:
$ pkg/vm/bin/snapshot_analysis.dart summary -b class -w dart:core profile.json
+-----------+------------------------+--------------+---------+----------+
| Library | Class | Size (Bytes) | Percent | Of total |
+-----------+------------------------+--------------+---------+----------+
| dart:core | _Uri | 43563 | 15.53% | 5.70% |
| dart:core | _StringBase | 28831 | 10.28% | 3.77% |
| dart:core | :: | 27559 | 9.83% | 3.60% |
| @other | | 25467 | 9.08% | 3.33% |
| dart:core | Uri | 14936 | 5.33% | 1.95% |
| dart:core | int | 12276 | 4.38% | 1.61% |
| dart:core | NoSuchMethodError | 12222 | 4.36% | 1.60% |
...
Here objects which can be attributed to _Uri
take 5.7%
of the snapshot,
at the same time objects which can be attributed to dart:core
library
but not to any specific class within this library take 3.33%
of the snapshot.
This command also supports estimating cumulative impact of a library or a
package together with its dependencies - which can be computed from
a precompiler trace (generated by adding
--trace-precompiler-to=path/to/trace.json
to --extra-gen-snapshot-options=
).
$ snapshot_analysis summary [-b granularity] [-w filter] [-s dep-tree-start-depth] [-d dep-tree-display-depth] --precompiler-trace=<input-trace.json> <input-profile.json>
For example:
$ snapshot_analysis summary -b package /tmp/profile.json
+-----------------------------+--------------+---------+
| Package | Size (Bytes) | Percent |
+-----------------------------+--------------+---------+
| package:compiler | 5369933 | 38.93% |
| package:front_end | 2644942 | 19.18% |
| package:kernel | 1443568 | 10.47% |
| package:_fe_analyzer_shared | 944555 | 6.85% |
...
$ snapshot_analysis summary -b package -s 1 -d 3 --precompiler-trace=/tmp/trace.json /tmp/profile.json
+------------------------------+--------------+---------+
| Package | Size (Bytes) | Percent |
+------------------------------+--------------+---------+
| package:compiler (+ 8 deps) | 5762761 | 41.78% |
| package:front_end (+ 1 deps) | 2708981 | 19.64% |
| package:kernel | 1443568 | 10.47% |
| package:_fe_analyzer_shared | 944555 | 6.85% |
...
Dependency trees:
package:compiler (total 5762761 bytes)
├── package:js_ast (total 242490 bytes)
├── package:dart2js_info (total 101280 bytes)
├── package:crypto (total 27434 bytes)
│ ├── package:typed_data (total 11850 bytes)
│ └── package:convert (total 5185 bytes)
├── package:collection (total 15182 bytes)
├── package:_js_interop_checks (total 4627 bytes)
└── package:js_runtime (total 1815 bytes)
package:front_end (total 2708981 bytes)
└── package:package_config (total 64039 bytes)
compare
$ snapshot_analysis compare [-b granularity] <old.json> <new.json>
This command shows comparison between two size profiles, allowing to understand changes to which part of the program contributed most to the change in the overall snapshot size.
$ pkg/vm/bin/snapshot_analysis.dart compare -b class old.json new.json
+------------------------+--------------------------+--------------+---------+
| Library | Class | Diff (Bytes) | Percent |
+------------------------+--------------------------+--------------+---------+
| dart:core | _SimpleUri | 11519 | 22.34% |
| dart:core | _Uri | 6563 | 12.73% |
| dart:io | _RandomAccessFile | 5337 | 10.35% |
| @other | | 4009 | 7.78% |
...
In this example 11519
more bytes can be attributed to _SimpleUri
class in
new.json
compared to old.json
.
treemap
$ snapshot_analysis treemap [--format <format>] <input.json> <output-dir>
$ google-chrome <output-dir>/index.html
This command generates treemap representation of the information from the
profile input.json
and stores it in output-dir
directory. Treemap can
later be viewed by opening <output-dir>/index.html
in the browser of your
choice.
--format
flag allows to control granularity of the output when input.json
is a V8 snapshot profile, available options are:
collapsed
essentially rendersProgramInfo
as a treemap, individual snapshot nodes are ignored.simplified
same ascollapsed
, but also folds size information from nested functions into outermost function (e.g. top level function or a method) producing easy to consume output.data-and-code
collapses snapshot nodes based on whether they represent data or executable code.object-type
(default) collapses snapshot nodes based on their type only.
explain
explain dynamic-calls
$ snapshot_analysis explain dynamic-calls <profile.json> <trace.json>
This command generates a report listing dynamically dispatched selectors and their approximate impact on the code size.
snapshot_analysis explain dynamic-calls /tmp/profile.json /tmp/trace.json
+------------------------------+--------------+---------+----------+
| Selector | Size (Bytes) | Percent | Of total |
+------------------------------+--------------+---------+----------+
| set:requestHeader | 10054 | 28.00% | 0.03% |
| get:scale | 3630 | 10.11% | 0.01% |
...
Dynamic call to set:requestHeader (retaining ~10054 bytes) occurs in:
package:my-super-app/src/injector.dart::Injector.handle{body}
Dynamic call to get:scale (retaining ~3630 bytes) occurs in:
package:some-dependency/src/image.dart::Image.==
API
This package can also be used as a building block for other packages which want to analyse VM AOT snapshots.
package:vm_snapshot_analysis/instruction_sizes.dart
provides helpers to read output of--print-instructions-sizes-to=...
package:vm_snapshot_analysis/v8_profile.dart
provides helpers to read output of--write-v8-snapshot-profile-to=...
Both formats can be converted into a ProgramInfo
structure which attempts
to breakdown snapshot size into hierarchical representation of the program
structure which can be understood by a Dart developer, attributing bytes
to packages, libraries, classes and functions.
package:vm_snapshot_analysis/utils.dart
contains helper methodloadProgramInfo
which automatically detects format of the input JSON file and createsProgramInfo
in an appropriate way, allowing to write code which works in the same way with both formats.
Precompiler Trace Format (--write-precompiler-trace-to=...
)
AOT compiler can produce a JSON file containing information about compiled functions and dependencies between them. This file has the following structure:
{
"trace": traceArray,
"entities": entitiesArray,
"strings": stringsArray,
}
-
stringsArray
is an array of strings referenced by other parts of the trace by their index in this array. -
entitiesArray
is an flattened array of entities:"C", <library-uri-idx>, <class-name-idx>, 0
- class record;"V", <class-idx>, <name-idx>, 0
- static field record;"F"|"S", <class-idx>, <name-idx>, <selector-id>
- function record (F
for dynamic functions andS
for static functions);
Note that all records in this array occupy the same amount of elements (
4
) to make random access by index possible. -
traceArray
is an flattened array of precompilation events:"R"
- root event (always the first element)"E"
- end event (always the last element)"C", <function-idx>
- function compilation event
Root and function compilation events can additionally be followed by a sequence of references which enumerate outgoing dependencies discovered by the AOT compiler:
<entity-idx>
- a reference to a function or a static field;"S", <selector-idx>
- a dynamic call with the given selector;"T", <selector-id>
- dispatch table call with the given selector id;
Flattened array is an array of records formed by consecutive elements:
[R0_0, R0_1, R0_2, R1_0, R1_1, R1_2, ...]
here R0_*
is the first record
and R1_*
is the second record and so on.
Features and bugs
Please file feature requests and bugs at the issue tracker.