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用於測量 GC 活動的 V8 垃圾收集器回調

[英]V8 garbage collector callbacks for measuring GC activity

 原文  2019-11-28 17:11:18  2   1    c++/ garbage-collection/ v8/ embedded-v8

問題描述

我有一個關於 V8 6.7.240 GC 行為和AddGCPrologueCallback / AddGCEpilogueCallback回調的小問題。

問題背后的一個小故事：我們使用 V8 引擎啟動自定義 JS 代碼，為了按時間限制執行，我們有一個watchdog （具有隔離- isolate->TerminateExecution()調用的單獨線程），它監視代碼並在長時間執行時殺死它正在運行，但與 GC 活動有關。

所以，如果代碼執行超時等於200ms ，GC活動需要300ms和代碼需要199ms ，我們會好起來的（ 199ms < 200ms ， 300ms不包括在內）。

在另一方面，如果代碼執行超時等於200ms ，GC活動發生300ms和代碼需要201ms ，這將是執行超時（ 201ms > 200ms ， 300ms ，不包含）。

如您所見，進行精確的 GC 測量非常重要，因為如果 GC 活動花費的時間超過回調所指示的時間，則可能導致watchdog會注意到代碼運行時間過長並殺死它，但實際上 GC 活動（連同“停止世界”的方法）“吃”時間沒有任何跡象。

似乎這正是我們在測試和調試過程中注意到的。 讓我們來看看：

V8側：

// init step
api,v8::Context::New
[api,v8::FunctionTemplate::New]

// a little bit fancy way of converting string to object
// like JSON:Parse call, but doing that using global JSON object
// no problem with that, just part of the log
api,v8::String::NewFromUtf8
api,v8::Object::Get
api,v8::String::NewFromUtf8
api,v8::Object::Get
api,v8::String::NewFromUtf8
timer-event-start,V8.GCIncrementalMarking,6406056058
timer-event-end,V8.GCIncrementalMarking,6406056581
api,v8::Function::Call

// actually function run
// script->Run(context);
timer-event-start,V8.Execute,6406057062
timer-event-start,V8.GCIncrementalMarking,6406057179
timer-event-end,V8.GCIncrementalMarking,6406059180
timer-event-start,V8.GCIncrementalMarking,6406060424
timer-event-end,V8.GCIncrementalMarking,6406062569
timer-event-start,V8.GCIncrementalMarking,6406063674
timer-event-end,V8.GCIncrementalMarking,6406065864
timer-event-start,V8.GCIncrementalMarking,6406066891
timer-event-end,V8.GCIncrementalMarking,6406068970
timer-event-start,V8.GCIncrementalMarking,6406069912
timer-event-end,V8.GCIncrementalMarking,6406070711
timer-event-start,V8.GCIncrementalMarking,6406071368
timer-event-end,V8.GCIncrementalMarking,6406073392
timer-event-start,V8.GCIncrementalMarking,6406074204
timer-event-end,V8.GCIncrementalMarking,6406076411
timer-event-start,V8.GCIncrementalMarking,6406077223
timer-event-end,V8.GCIncrementalMarking,6406079326
timer-event-start,V8.GCIncrementalMarking,6406080096
timer-event-end,V8.GCIncrementalMarking,6406082253
timer-event-start,V8.GCIncrementalMarking,6406083041
timer-event-end,V8.GCIncrementalMarking,6406085169
timer-event-start,V8.GCIncrementalMarking,6406085754
timer-event-end,V8.GCIncrementalMarking,6406087852
timer-event-start,V8.GCIncrementalMarking,6406088753
timer-event-end,V8.GCIncrementalMarking,6406090888
timer-event-start,V8.GCIncrementalMarking,6406091704
timer-event-end,V8.GCIncrementalMarking,6406093860
timer-event-start,V8.GCIncrementalMarking,6406094638
timer-event-end,V8.GCIncrementalMarking,6406096819
timer-event-start,V8.GCIncrementalMarking,6406097737
timer-event-end,V8.GCIncrementalMarking,6406099851
timer-event-start,V8.GCIncrementalMarking,6406100651
timer-event-end,V8.GCIncrementalMarking,6406102158
timer-event-start,V8.GCIncrementalMarking,6406102830
timer-event-end,V8.GCIncrementalMarking,6406102949
timer-event-start,V8.GCIncrementalMarkingFinalize,6406103476
timer-event-end,V8.GCIncrementalMarkingFinalize,6406103720
timer-event-start,V8.GCIncrementalMarking,6406103781
timer-event-end,V8.GCIncrementalMarking,6406103805
timer-event-start,V8.GCFinalizeMC,6406106106
markcompact,begin,37,733899,1573929817539
sfi-move,0x26c8c6b42258,0x39727ab446f0
sfi-move,0x26c8c6b423d0,0x39727ab44858
code-move,0x26c8c6b424a8,0x39727ab44920
code-move,0x26c8c6b42990,0x39727ab44e08
[delete,MemoryChunk,0x20803a500000]
markcompact,end,37,750515,1573929817560
timer-event-end,V8.GCFinalizeMC,6406126613
[delete,MemoryChunk,0x2fcf14300000]
timer-event-start,V8.GCIncrementalMarkingStart,
timer-event-end,V8.GCIncrementalMarkingStart,6406148920
timer-event-start,V8.GCIncrementalMarking,6406148975
timer-event-end,V8.GCIncrementalMarking,6406150059
timer-event-start,V8.GCIncrementalMarking,6406151014
timer-event-end,V8.GCIncrementalMarking,6406152657
timer-event-start,V8.GCIncrementalMarking,6406153356
timer-event-end,V8.GCIncrementalMarking,6406154995
timer-event-start,V8.GCIncrementalMarking,6406155703
timer-event-end,V8.GCIncrementalMarking,6406157341
new,MemoryChunk,0x24eee1900000,524288
timer-event-start,V8.GCIncrementalMarking,6406158486
timer-event-end,V8.GCIncrementalMarking,6406160149
new,MemoryChunk,0x7f310200000,524288
timer-event-start,V8.GCIncrementalMarking,6406161218
timer-event-end,V8.GCIncrementalMarking,6406162914
new,MemoryChunk,0x178aad500000,524288
timer-event-start,V8.GCIncrementalMarking,6406163990
timer-event-end,V8.GCIncrementalMarking,6406165681
new,MemoryChunk,0x34d7b2580000,524288
timer-event-start,V8.GCIncrementalMarking,6406166748
timer-event-end,V8.GCIncrementalMarking,6406168439
new,MemoryChunk,0x225fec080000,524288
timer-event-start,V8.GCIncrementalMarking,6406169481
timer-event-end,V8.GCIncrementalMarking,6406171229
new,MemoryChunk,0x502e7380000,524288
timer-event-start,V8.GCIncrementalMarking,6406172280
timer-event-end,V8.GCIncrementalMarking,6406174003
new,MemoryChunk,0x208b2af00000,524288
timer-event-start,V8.GCIncrementalMarking,6406175047
timer-event-end,V8.GCIncrementalMarking,6406176787
new,MemoryChunk,0x39ffd8400000,524288
timer-event-start,V8.GCIncrementalMarking,6406177851
timer-event-end,V8.GCIncrementalMarking,6406179600
new,MemoryChunk,0x10408d480000,524288
timer-event-start,V8.GCIncrementalMarking,6406180631
timer-event-end,V8.GCIncrementalMarking,6406182384
new,MemoryChunk,0x25c069e80000,524288
timer-event-start,V8.GCIncrementalMarking,6406183415
timer-event-end,V8.GCIncrementalMarking,6406185165
new,MemoryChunk,0x20cb51c80000,524288
timer-event-start,V8.GCIncrementalMarking,6406186210
timer-event-end,V8.GCIncrementalMarking,6406186919
new,MemoryChunk,0xe774a300000,524288
timer-event-start,V8.GCIncrementalMarking,6406187940
timer-event-end,V8.GCIncrementalMarking,6406188387
new,MemoryChunk,0x23a0a1180000,524288
timer-event-start,V8.GCIncrementalMarking,6406189172
timer-event-end,V8.GCIncrementalMarking,6406189924
new,MemoryChunk,0x16bb70600000,524288
timer-event-start,V8.GCIncrementalMarking,6406190724
timer-event-end,V8.GCIncrementalMarking,6406192029
new,MemoryChunk,0x18b8a0200000,524288
timer-event-start,V8.GCIncrementalMarking,6406192894
timer-event-end,V8.GCIncrementalMarking,6406194253
new,MemoryChunk,0x11c87c180000,524288
timer-event-start,V8.GCIncrementalMarking,6406195137
timer-event-end,V8.GCIncrementalMarking,6406196462
new,MemoryChunk,0x353b80280000,524288
timer-event-start,V8.GCIncrementalMarking,6406197381
timer-event-end,V8.GCIncrementalMarking,6406198513
new,MemoryChunk,0x991e5a80000,524288
timer-event-start,V8.GCIncrementalMarking,6406199347
timer-event-end,V8.GCIncrementalMarking,6406200659
new,MemoryChunk,0x77559500000,524288
timer-event-start,V8.GCIncrementalMarking,6406201554
timer-event-end,V8.GCIncrementalMarking,6406202952
new,MemoryChunk,0x51fcc580000,524288
timer-event-start,V8.GCIncrementalMarking,6406203842
timer-event-end,V8.GCIncrementalMarking,6406205229
new,MemoryChunk,0x11134ca80000,524288
timer-event-start,V8.GCIncrementalMarking,6406206124
timer-event-end,V8.GCIncrementalMarking,6406207561
new,MemoryChunk,0x17b32eb00000,524288
timer-event-start,V8.GCIncrementalMarking,6406208473
timer-event-end,V8.GCIncrementalMarking,6406209913
new,MemoryChunk,0xa7929400000,524288
timer-event-start,V8.GCIncrementalMarking,6406210795
timer-event-end,V8.GCIncrementalMarking,6406212249
new,MemoryChunk,0x1f76e7200000,524288
timer-event-start,V8.GCIncrementalMarking,6406213115
timer-event-end,V8.GCIncrementalMarking,6406214629
new,MemoryChunk,0x4bb9cd00000,524288
timer-event-start,V8.GCIncrementalMarking,6406215548
timer-event-end,V8.GCIncrementalMarking,6406216079
new,MemoryChunk,0x26fd04080000,524288
timer-event-start,V8.GCIncrementalMarking,6406216911
timer-event-end,V8.GCIncrementalMarking,6406217106
timer-event-start,V8.GCIncrementalMarkingFinalize,6406217606
timer-event-end,V8.GCIncrementalMarkingFinalize,6406217921
new,MemoryChunk,0x3e8b51000000,524288
timer-event-start,V8.GCIncrementalMarking,6406218332
timer-event-end,V8.GCIncrementalMarking,6406218348
timer-event-start,V8.GCFinalizeMC,6406218897
markcompact,begin,38,36462,1573929817653
markcompact,end,38,54306,1573929817670
timer-event-end,V8.GCFinalizeMC,6406237199
new,MemoryChunk,0x3e70a1a00000,524288
new,MemoryChunk,0x14c9e4180000,524288
new,MemoryChunk,0x335947c80000,524288
timer-event-start,V8.GCIncrementalMarkingStart,6406263779
timer-event-end,V8.GCIncrementalMarkingStart,6406264145
new,MemoryChunk,0x1bf6fd00000,524288
timer-event-start,V8.GCIncrementalMarking,6406264575
timer-event-end,V8.GCIncrementalMarking,6406266175
new,MemoryChunk,0x109d6f780000,524288
timer-event-start,V8.GCIncrementalMarking,6406267498
timer-event-end,V8.GCIncrementalMarking,6406269125
new,MemoryChunk,0xcf3b9200000,524288
timer-event-start,V8.GCIncrementalMarking,6406270226
timer-event-end,V8.GCIncrementalMarking,6406271868
new,MemoryChunk,0x33eb2c880000,524288
timer-event-start,V8.GCIncrementalMarking,6406272919
timer-event-end,V8.GCIncrementalMarking,6406274608
new,MemoryChunk,0x10c056a80000,524288
timer-event-start,V8.GCIncrementalMarking,6406275660
timer-event-end,V8.GCIncrementalMarking,6406277318
new,MemoryChunk,0x1846c1880000,524288
timer-event-start,V8.GCIncrementalMarking,6406278406
timer-event-end,V8.GCIncrementalMarking,6406280119
new,MemoryChunk,0x21eed5900000,524288
timer-event-start,V8.GCIncrementalMarking,6406281176
timer-event-end,V8.GCIncrementalMarking,6406282888
new,MemoryChunk,0x323ac6b80000,524288
timer-event-start,V8.GCIncrementalMarking,6406283954
timer-event-end,V8.GCIncrementalMarking,6406285682
new,MemoryChunk,0x3c2009d00000,524288
timer-event-start,V8.GCIncrementalMarking,6406286739
timer-event-end,V8.GCIncrementalMarking,6406288466
new,MemoryChunk,0x3d504cd00000,524288
timer-event-start,V8.GCIncrementalMarking,6406289535
timer-event-end,V8.GCIncrementalMarking,6406291291
new,MemoryChunk,0x235494980000,524288
timer-event-start,V8.GCIncrementalMarking,6406292373
timer-event-end,V8.GCIncrementalMarking,6406294127
new,MemoryChunk,0xecfc3600000,524288
timer-event-start,V8.GCIncrementalMarking,6406295191
timer-event-end,V8.GCIncrementalMarking,6406296997
new,MemoryChunk,0x1a2eae600000,524288
timer-event-start,V8.GCIncrementalMarking,6406298083
timer-event-end,V8.GCIncrementalMarking,6406299894
timer-event-end,V8.Execute,6406300603

應用端：

(1) // kGCTypeIncrementalMarking
[18:43:37.536(1573929817536752)][DEBUG]: GCPrologueCallback type: 4
[18:43:37.536(1573929817536955)][DEBUG]: GCEpilogCallback type: 4
Total: 203 micro


(2) // kGCTypeMarkSweepCompact
[18:43:37.539(1573929817539368)][DEBUG]: GCPrologueCallback type: 2
[18:43:37.559(1573929817559840)][DEBUG]: GCEpilogCallback type: 2
Total: 20472 micro


(3) // kGCTypeIncrementalMarking
[18:43:37.650(1573929817650874)][DEBUG]: GCPrologueCallback type: 4
[18:43:37.651(1573929817651154)][DEBUG]: GCEpilogCallback type: 4
Total: 280 micro


(4) // kGCTypeMarkSweepCompact
[18:43:37.652(1573929817652160)][DEBUG]: GCPrologueCallback type: 2
[18:43:37.670(1573929817670422)][DEBUG]: GCEpilogCallback type: 2
Total: 18262 micro

因此，總共 39217 微秒或 40 毫秒。

那種方式讀取V8日志太復雜了。 所以我通過測量timer-event-start / timer-event-end事件之間的時間對其進行了一些后處​​理。

(V8.GCIncrementalMarking, 523)
(V8.GCIncrementalMarking, 2001)
(V8.GCIncrementalMarking, 2145)
(V8.GCIncrementalMarking, 2190)
(V8.GCIncrementalMarking, 2079)
(V8.GCIncrementalMarking, 799)
(V8.GCIncrementalMarking, 2024)
(V8.GCIncrementalMarking, 2207)
(V8.GCIncrementalMarking, 2103)
(V8.GCIncrementalMarking, 2157)
(V8.GCIncrementalMarking, 2128)
(V8.GCIncrementalMarking, 2098)
(V8.GCIncrementalMarking, 2135)
(V8.GCIncrementalMarking, 2156)
(V8.GCIncrementalMarking, 2181)
(V8.GCIncrementalMarking, 2114)
(V8.GCIncrementalMarking, 1507)
(V8.GCIncrementalMarking, 119)
(V8.GCIncrementalMarkingFinalize, 244)        (1)
(V8.GCIncrementalMarking, 24)
(V8.GCFinalizeMC, 20507)                      (2)
(V8.GCIncrementalMarkingStart, 428)
(V8.GCIncrementalMarking, 1084)
(V8.GCIncrementalMarking, 1643)
(V8.GCIncrementalMarking, 1639)
(V8.GCIncrementalMarking, 1638)
(V8.GCIncrementalMarking, 1663)
(V8.GCIncrementalMarking, 1696)
(V8.GCIncrementalMarking, 1691)
(V8.GCIncrementalMarking, 1691)
(V8.GCIncrementalMarking, 1748)
(V8.GCIncrementalMarking, 1723)
(V8.GCIncrementalMarking, 1740)
(V8.GCIncrementalMarking, 1749)
(V8.GCIncrementalMarking, 1753)
(V8.GCIncrementalMarking, 1750)
(V8.GCIncrementalMarking, 709)
(V8.GCIncrementalMarking, 447)
(V8.GCIncrementalMarking, 752)
(V8.GCIncrementalMarking, 1305)
(V8.GCIncrementalMarking, 1359)
(V8.GCIncrementalMarking, 1325)
(V8.GCIncrementalMarking, 1132)
(V8.GCIncrementalMarking, 1312)
(V8.GCIncrementalMarking, 1398)
(V8.GCIncrementalMarking, 1387)
(V8.GCIncrementalMarking, 1437)
(V8.GCIncrementalMarking, 1440)
(V8.GCIncrementalMarking, 1454)
(V8.GCIncrementalMarking, 1514)
(V8.GCIncrementalMarking, 531)
(V8.GCIncrementalMarking, 195)
(V8.GCIncrementalMarkingFinalize, 315)        (3)
(V8.GCIncrementalMarking, 16)
(V8.GCFinalizeMC, 18302)                      (4)
(V8.GCIncrementalMarkingStart, 366)
(V8.GCIncrementalMarking, 1600)
(V8.GCIncrementalMarking, 1627)
(V8.GCIncrementalMarking, 1642)
(V8.GCIncrementalMarking, 1689)
(V8.GCIncrementalMarking, 1658)
(V8.GCIncrementalMarking, 1713)
(V8.GCIncrementalMarking, 1712)
(V8.GCIncrementalMarking, 1728)
(V8.GCIncrementalMarking, 1727)
(V8.GCIncrementalMarking, 1756)
(V8.GCIncrementalMarking, 1754)
(V8.GCIncrementalMarking, 1806)
(V8.GCIncrementalMarking, 1811)
(Total, 135996)

正如您所看到的，我們只能匹配 4 個案例，但是沒有注意到許多GCIncrementalMarking活動。 而真正的總時間等於 136ms。 遠遠超過 40 毫秒！，我們能夠在應用程序方面進行測量。

我知道 Orinoco 和並行方法，但我不知道對GCIncrementalMarking調用是否GCIncrementalMarking阻止代碼執行。

我們已經多次注意到相同的情況，在所有情況下，與 V8 日志文件相比，代碼終止的原因是應用程序端的 GC 測量不正確。

這是故意的，我們不能如此信任 GC 回調嗎？ 或者我錯過了什么？ 作為臨時解決方案，我們已將 V8 降級到5.6.316 ，它可以正常工作。

6.7.240有新的 GC 方法，它會是那個問題的根源嗎？

附注。 --single-threaded-gc for 6.7.240也沒有幫助

聚苯乙烯。 一些與 V8 和 GC 邏輯相關的代碼：

void cnode::V8Runner::init() {    
    v8::V8::InitializeICU();

    v8::Platform *platform = v8::platform::CreateDefaultPlatform();
    v8::V8::InitializePlatform(platform);
    v8::V8::Initialize();

    auto flags = "--log --log-all --logfile=/tmp/v8.log --nolazy";
    auto isolate = cnode::V8Runner::getIsolate();

    isolate->AddGCPrologueCallback(cnode::V8Runner::_GCPrologue);
    isolate->AddGCEpilogueCallback(cnode::V8Runner::_GCEpilog);
}

void cnode::V8Runner::_GCPrologue(v8::Isolate *isolate, v8::GCType type,
                                  v8::GCCallbackFlags flags) {    
    cnode::V8Runner::_GCPrologueTimePoint = std::chrono::high_resolution_clock::now();
    cnode::V8Runner::_GCEpilogTimePoint = std::chrono::high_resolution_clock::now();

    LOG_DEBUG("GCPrologueCallback type: %d", type);
}

void cnode::V8Runner::_GCEpilog(v8::Isolate *isolate, v8::GCType type,
                                v8::GCCallbackFlags flags) {    
    cnode::V8Runner::_GCEpilogTimePoint = std::chrono::high_resolution_clock::now();

    std::chrono::milliseconds _GCPrologueTimePointMs = std::chrono::duration_cast<std::chrono::milliseconds>(
            cnode::V8Runner::_GCPrologueTimePoint.time_since_epoch());
    std::chrono::milliseconds _GCEpilogTimePointMs = std::chrono::duration_cast<std::chrono::milliseconds>(
            cnode::V8Runner::_GCEpilogTimePoint.time_since_epoch());

    const int diff = _GCEpilogTimePointMs.count() - _GCPrologueTimePointMs.count();

    cnode::V8Runner::_currentGCActionMs += diff;

    cnode::V8Runner::_GCPrologueTimePoint = std::chrono::high_resolution_clock::now();
    cnode::V8Runner::_GCEpilogTimePoint = std::chrono::high_resolution_clock::now();

    LOG_DEBUG("GCEpilogCallback type: %d", type);
}

購買力平價。 在這篇文章之后，我決定在每次代碼執行后手動調用Isolate::LowMemoryNotification()來重新檢查這一點。

原始 V8 日志：

api,v8::Context::New
api,v8::FunctionTemplate::New
api,v8::ObjectTemplate::New
[api,v8::FunctionTemplate::New]
api,v8::String::NewFromUtf8
api,v8::JSON::Parse
[new,MemoryChunk,0x1940b7d00000,524288]
timer-event-start,V8.GCIncrementalMarkingStart,4351782723
timer-event-end,V8.GCIncrementalMarkingStart,4351783066
new,MemoryChunk,0x106dca200000,524288
timer-event-start,V8.GCIncrementalMarking,4351783463
timer-event-end,V8.GCIncrementalMarking,4351785131
new,MemoryChunk,0x225019c00000,524288
timer-event-start,V8.GCIncrementalMarking,4351786485
timer-event-end,V8.GCIncrementalMarking,4351788194
new,MemoryChunk,0xdfc50c80000,524288
timer-event-start,V8.GCIncrementalMarking,4351789202
timer-event-end,V8.GCIncrementalMarking,4351790879
new,MemoryChunk,0x26861a780000,524288
timer-event-start,V8.GCIncrementalMarking,4351791905
timer-event-end,V8.GCIncrementalMarking,4351793611
new,MemoryChunk,0x44086a00000,524288
timer-event-start,V8.GCIncrementalMarking,4351794615
timer-event-end,V8.GCIncrementalMarking,4351796319
new,MemoryChunk,0x4debd600000,524288
timer-event-start,V8.GCIncrementalMarking,4351797315
timer-event-end,V8.GCIncrementalMarking,4351799066
new,MemoryChunk,0x2db69c500000,524288
timer-event-start,V8.GCIncrementalMarking,4351800060
timer-event-end,V8.GCIncrementalMarking,4351801814
new,MemoryChunk,0x1f1825000000,524288
timer-event-start,V8.GCIncrementalMarking,4351802804
timer-event-end,V8.GCIncrementalMarking,4351804535
new,MemoryChunk,0x86246080000,524288
timer-event-start,V8.GCIncrementalMarking,4351805573
timer-event-end,V8.GCIncrementalMarking,4351807383
new,MemoryChunk,0xfc3bb580000,524288
timer-event-start,V8.GCIncrementalMarking,4351808377
timer-event-end,V8.GCIncrementalMarking,4351810192
new,MemoryChunk,0x10451e500000,524288
timer-event-start,V8.GCIncrementalMarking,4351811223
timer-event-end,V8.GCIncrementalMarking,4351813019
new,MemoryChunk,0x16e643c00000,524288
timer-event-start,V8.GCIncrementalMarking,4351814010
timer-event-end,V8.GCIncrementalMarking,4351815842
new,MemoryChunk,0x2a4379600000,524288
timer-event-start,V8.GCIncrementalMarking,4351816837
timer-event-end,V8.GCIncrementalMarking,4351818621
new,MemoryChunk,0x18436f400000,524288
timer-event-start,V8.GCIncrementalMarking,4351819650
timer-event-end,V8.GCIncrementalMarking,4351821491
new,MemoryChunk,0x3b377700000,524288
timer-event-start,V8.GCIncrementalMarking,4351822503
timer-event-end,V8.GCIncrementalMarking,4351824007
new,MemoryChunk,0x1f2f22600000,524288
timer-event-start,V8.GCIncrementalMarking,4351825011
timer-event-end,V8.GCIncrementalMarking,4351825827
new,MemoryChunk,0x1cd733a80000,524288
timer-event-start,V8.GCIncrementalMarking,4351826871
timer-event-end,V8.GCIncrementalMarking,4351827291
new,MemoryChunk,0x3cf039a80000,524288
timer-event-start,V8.GCIncrementalMarking,4351828058
timer-event-end,V8.GCIncrementalMarking,4351828500
new,MemoryChunk,0x31ae7100000,524288
timer-event-start,V8.GCIncrementalMarking,4351829286
timer-event-end,V8.GCIncrementalMarking,4351830586    
new,MemoryChunk,0x2265e4c00000,524288
timer-event-start,V8.GCIncrementalMarking,4351831462
timer-event-end,V8.GCIncrementalMarking,4351832806
new,MemoryChunk,0x34586ae00000,524288
timer-event-start,V8.GCIncrementalMarking,4351833700
timer-event-end,V8.GCIncrementalMarking,4351835122
new,MemoryChunk,0x21c0aa580000,524288    
timer-event-start,V8.GCIncrementalMarking,4351836000
timer-event-end,V8.GCIncrementalMarking,4351837409
new,MemoryChunk,0x2d29cda00000,524288
timer-event-start,V8.GCIncrementalMarking,4351838280
timer-event-end,V8.GCIncrementalMarking,4351839701
new,MemoryChunk,0x216cbbb80000,524288
timer-event-start,V8.GCIncrementalMarking,4351840569
timer-event-end,V8.GCIncrementalMarking,4351842015
new,MemoryChunk,0x1fb82e480000,524288
timer-event-start,V8.GCIncrementalMarking,4351842910
timer-event-end,V8.GCIncrementalMarking,4351844380
new,MemoryChunk,0x329529f00000,524288
timer-event-start,V8.GCIncrementalMarking,4351845255
timer-event-end,V8.GCIncrementalMarking,4351846654    
new,MemoryChunk,0x957ccf80000,524288
timer-event-start,V8.GCIncrementalMarking,4351847553
timer-event-end,V8.GCIncrementalMarking,4351848991
new,MemoryChunk,0x2df008e00000,524288
timer-event-start,V8.GCIncrementalMarking,4351849864
timer-event-end,V8.GCIncrementalMarking,4351851358
new,MemoryChunk,0x8be2be80000,524288
timer-event-start,V8.GCIncrementalMarking,4351852237
timer-event-end,V8.GCIncrementalMarking,4351853720
new,MemoryChunk,0x146846980000,524288
timer-event-start,V8.GCIncrementalMarking,4351854588
timer-event-end,V8.GCIncrementalMarking,4351856080
new,MemoryChunk,0x367cfe280000,524288
timer-event-start,V8.GCIncrementalMarking,4351856969
timer-event-end,V8.GCIncrementalMarking,4351858491
new,MemoryChunk,0x6ed38180000,524288
timer-event-start,V8.GCIncrementalMarking,4351859382
timer-event-end,V8.GCIncrementalMarking,4351860900
new,MemoryChunk,0xfbd5f600000,524288
timer-event-start,V8.GCIncrementalMarking,4351861805
timer-event-end,V8.GCIncrementalMarking,4351863367
new,MemoryChunk,0x1a5e01680000,524288
timer-event-start,V8.GCIncrementalMarking,4351864277
timer-event-end,V8.GCIncrementalMarking,4351865092
new,MemoryChunk,0x24120d700000,524288
timer-event-start,V8.GCIncrementalMarking,4351865984
timer-event-end,V8.GCIncrementalMarking,4351866048
new,MemoryChunk,0x125d39480000,524288
timer-event-start,V8.GCIncrementalMarking,4351866808
timer-event-end,V8.GCIncrementalMarking,4351866824
timer-event-start,V8.GCIncrementalMarkingFinalize,4351867246
timer-event-end,V8.GCIncrementalMarkingFinalize,4351867419
new,MemoryChunk,0x2f31d9400000,524288
timer-event-start,V8.GCIncrementalMarking,4351867767
timer-event-end,V8.GCIncrementalMarking,4351867774
timer-event-start,V8.GCFinalizeMC,4351869855
markcompact,begin,7143,825650,1575032707066
markcompact,end,7143,846265,1575032707086
timer-event-end,V8.GCFinalizeMC,4351890363
[new,MemoryChunk,0x19b52bb00000,524288]
timer-event-start,V8.GCLowMemoryNotification,4351984850
timer-event-start,V8.GCCompactor,4351984910
markcompact,begin,7143,949018,1575032707181
[delete,MemoryChunk,0xd202f700000]
markcompact,end,7144,188469,1575032707268
timer-event-end,V8.GCCompactor,4352073048
[delete,MemoryChunk,0x1c887fa80000]    
timer-event-start,V8.GCCompactor,4352073343
markcompact,begin,7144,192691,1575032707270
new,MemoryChunk,0x33c543500000,524288
new,MemoryChunk,0xd4241800000,524288
[sfi-move,0x8b6f5421390,0xd424181d470]
[delete,MemoryChunk,0x1455b1780000]
markcompact,end,7144,453893,1575032707371
timer-event-end,V8.GCCompactor,4352175676
delete,MemoryChunk,0x25fae9b80000
delete,MemoryChunk,0x2590e9700000
timer-event-end,V8.GCLowMemoryNotification,4352175844
api,v8::ObjectTemplate::New
api,v8::FunctionTemplate::New
api,v8::String::NewFromUtf8

應用日志：

(1) // kGCTypeIncrementalMarking
[13:05:07.063(1575032707063270)][DEBUG]: GCPrologueCallback type: 4
[13:05:07.063(1575032707063418)][DEBUG]: GCEpilogCallback type: 4
Total: 148micro

(2) // kGCTypeMarkSweepCompact
[13:05:07.065(1575032707065876)][DEBUG]: GCPrologueCallback type: 2
[13:05:07.086(1575032707086356)][DEBUG]: GCEpilogCallback type: 2
Total: 20480 micro

(3) // kGCTypeMarkSweepCompact
[13:05:07.180(1575032707180925)][DEBUG]: GCPrologueCallback type: 2
[13:05:07.269(1575032707269036)][DEBUG]: GCEpilogCallback type: 2

(4) // kGCTypeMarkSweepCompact
[13:05:07.269(1575032707269366)][DEBUG]: GCPrologueCallback type: 2
[13:05:07.371(1575032707371667)][DEBUG]: GCEpilogCallback type: 2

后處理后的V8日志：

(V8.GCIncrementalMarkingStart, 343)          (1)?
(V8.GCIncrementalMarking, 1668)
(V8.GCIncrementalMarking, 1709)
(V8.GCIncrementalMarking, 1677)
(V8.GCIncrementalMarking, 1706)
(V8.GCIncrementalMarking, 1704)
(V8.GCIncrementalMarking, 1751)
(V8.GCIncrementalMarking, 1754)
(V8.GCIncrementalMarking, 1731)
(V8.GCIncrementalMarking, 1810)
(V8.GCIncrementalMarking, 1815)
(V8.GCIncrementalMarking, 1796)
(V8.GCIncrementalMarking, 1832)
(V8.GCIncrementalMarking, 1784)
(V8.GCIncrementalMarking, 1841)
(V8.GCIncrementalMarking, 1504)
(V8.GCIncrementalMarking, 816)
(V8.GCIncrementalMarking, 420)
(V8.GCIncrementalMarking, 442)
(V8.GCIncrementalMarking, 1300)
(V8.GCIncrementalMarking, 1344)
(V8.GCIncrementalMarking, 1422)
(V8.GCIncrementalMarking, 1409)
(V8.GCIncrementalMarking, 1421)
(V8.GCIncrementalMarking, 1446)
(V8.GCIncrementalMarking, 1470)
(V8.GCIncrementalMarking, 1399)
(V8.GCIncrementalMarking, 1438)
(V8.GCIncrementalMarking, 1494)
(V8.GCIncrementalMarking, 1483)
(V8.GCIncrementalMarking, 1492)
(V8.GCIncrementalMarking, 1522)
(V8.GCIncrementalMarking, 1518)
(V8.GCIncrementalMarking, 1562)
(V8.GCIncrementalMarking, 815)
(V8.GCIncrementalMarking, 64)
(V8.GCIncrementalMarking, 16)
(V8.GCIncrementalMarkingFinalize, 173)
(V8.GCIncrementalMarking, 7)
(V8.GCFinalizeMC, 20508)                  (2)
// call to LowMemoryNotification
(V8.GCCompactor, 88138)                   (3)
(V8.GCCompactor, 102333)                  (4)
(V8.GCLowMemoryNotification, 190994)
(Total, 452871)

當我看到這個的時候，我的第一個想法是 - V8.GCLoWMemoryNotification (190994) 包括 V8.GCCompactor(88138) 和 V8.GCCompactor(102333)..畢竟 (88138 + 102333) < 190994，這是有道理的，對吧？

因此，可能V8.GCIncrementalMarking也包含在V8.GCFinalizeMC 。 但事實證明並非如此 - 20508遠小於GCIncrementalMarking s 值的數量（ 50555 ）。

這個故事的最終結果是一樣的——執行超時。 代碼的時間限制等於200ms 。

對LowMemoryNotification調用不包括在watchdog監控中。 所以452871 - 190994 = 261877 。

請記住，我們尊重 GC 活動，因此261877 - 20508 = 241369 。 仍然大於200ms。

但是，如果我們開始計算所有V8.GCIncrementalMarking活動（ 50555微秒），最終結果將是241369 - 50555 = 190814 。 190ms - 不是超時！

我仍然認為 V8 ( 6.7.240 ) 在 GC 活動方面沒有提供足夠的准確性。

1 個解決方案

解決方案1
 3  2019-12-04 11:22:11

V8 開發人員在這里。 如果我正確理解了這個問題，那么答案是：在主要 GC 周期的開始/結束時調用 GC 序言/尾聲回調，其中包括（可能是數百個）增量標記步驟和最后一個稍長的完成階段，所有這些都與常規程序執行混合在一起。 回調不會在每個增量標記步驟周圍調用，也不會在次要 GC 周期（“scavenges”，奇怪的是上面的各種日志中完全沒有）調用，並且不打算提供精確的時間信息。 對不起。

理想情況下，您不必執行任何這些操作。 對於大多數程序，花在 GC 上的時間占總執行時間的 1% 到 10% 之間，所以應該沒什么關系。

如果您確實堅持跟蹤在主要 GC 上花費的主線程時間，那么最好的辦法可能是關閉增量標記（標志--noincremental-marking ）。 請注意，這將使用戶體驗更加不穩定（而不是數百次 1 毫秒以下的停頓，您會得到幾秒鍾的停頓），但也許在您的場景中您並不關心。 我沒有關於涵蓋次要 GC 的建議。

也就是說，如果您允許進行更一般的評論，我對整體方法表示懷疑。 GC 活動由分配觸發，可以看作是分配成本的一部分。 如果您的目標是“公平地”對待程序（甚至可能是競爭性的？），那么我絕對會將 GC 時間包括在每個程序的時間預算中。 GC 不是“突然隨機攻擊表現良好的代碼”——不得不花時間在 GC 活動上是分配大量代碼的情況； 如果代碼想要保持在一定的時間預算內，那么最好嘗試盡可能少地分配，這只是快速/高效的一方面。

也許底層的心理模型是一種非常簡單的內存管理策略，例如，許多代碼片段可以在沒有任何 GC 活動的情況下運行，並為每個代碼片段分配幾兆字節，然后其中之一是壓倒駱駝的不幸稻草，越過某個門檻，並以重大減速運行以清理其他人留下的垃圾？ 在這樣的 VM 中，您的方法完全有意義，但這與 V8 的工作方式相去甚遠。

此外，GC 不是主線程的唯一中斷，還有（前台部分）函數優化，它周圍沒有任何嵌入器控制的回調。 如果您想排除所有中斷，則必須破解 V8 以創建一種方法來排除這些中斷。 另一方面，我上面的論點也適用於這里：優化不會隨機發生，它發生在長時間運行的代碼中，並且通常有利於整體性能（否則我們不會這樣做），所以我認為它會公平/適當地將它包括在預算中，就像 GC 時間一樣。

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