Issue 6215065: code review 6215065: runtime: faster GC sweep phase

Issue 6215065: code review 6215065: runtime: faster GC sweep phase (Closed)

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Created:
14 years ago by dvyukov

Modified:
14 years ago

Reviewers:

CC:
golang-dev

Visibility:
Public.

Description

runtime: faster GC sweep phase benchmark old ns/op new ns/op delta garbage.BenchmarkParser 3731065750 3715543750 -0.41% garbage.BenchmarkParser-2 3631299750 3495248500 -3.75% garbage.BenchmarkParser-4 3386486000 3339353000 -1.39% garbage.BenchmarkParser-8 3267632000 3286422500 +0.58% garbage.BenchmarkParser-16 3299203000 3316081750 +0.51% garbage.BenchmarkTree 977532888 919453833 -5.94% garbage.BenchmarkTree-2 919948555 853478000 -7.23% garbage.BenchmarkTree-4 841329000 790207000 -6.08% garbage.BenchmarkTree-8 787792777 740380666 -6.01% garbage.BenchmarkTree-16 899257166 846594555 -5.86% garbage.BenchmarkTree2 574876300 571885800 -0.52% garbage.BenchmarkTree2-2 348162700 345888900 -0.65% garbage.BenchmarkTree2-4 184912500 179137000 -3.22% garbage.BenchmarkTree2-8 104243900 103485600 -0.73% garbage.BenchmarkTree2-16 97269500 85137100 -14.25% garbage.BenchmarkParserPause 141101976 157746974 +11.80% garbage.BenchmarkParserPause-2 103096051 83043048 -19.45% garbage.BenchmarkParserPause-4 52153133 45951111 -11.89% garbage.BenchmarkParserPause-8 36730190 38901024 +5.91% garbage.BenchmarkParserPause-16 32678875 29578585 -9.49% garbage.BenchmarkTreePause 29487065 29648439 +0.55% garbage.BenchmarkTreePause-2 22443494 21306159 -5.07% garbage.BenchmarkTreePause-4 15799691 14985647 -5.15% garbage.BenchmarkTreePause-8 10768112 9531420 -12.97% garbage.BenchmarkTreePause-16 16329891 15205158 -6.89% garbage.BenchmarkTree2Pause 2586957240 2577533200 -0.36% garbage.BenchmarkTree2Pause-2 1683383760 1673923800 -0.56% garbage.BenchmarkTree2Pause-4 1102860320 1074040280 -2.68% garbage.BenchmarkTree2Pause-8 902627920 886122400 -1.86% garbage.BenchmarkTree2Pause-16 856470920 804152320 -6.50% garbage.BenchmarkParserLastPause 277316000 280839000 +1.25% garbage.BenchmarkParserLastPause-2 179446000 163687000 -8.78% garbage.BenchmarkParserLastPause-4 106752000 94144000 -11.81% garbage.BenchmarkParserLastPause-8 57758000 61640000 +6.72% garbage.BenchmarkParserLastPause-16 51235000 42552000 -16.95% garbage.BenchmarkTreeLastPause 45244000 50786000 +12.25% garbage.BenchmarkTreeLastPause-2 37163000 34654000 -6.75% garbage.BenchmarkTreeLastPause-4 24178000 21967000 -9.14% garbage.BenchmarkTreeLastPause-8 20390000 15648000 -30.30% garbage.BenchmarkTreeLastPause-16 22398000 20180000 -9.90% garbage.BenchmarkTree2LastPause 5748706000 5718809000 -0.52% garbage.BenchmarkTree2LastPause-2 3481570000 3458844000 -0.65% garbage.BenchmarkTree2LastPause-4 1849073000 1791330000 -3.22% garbage.BenchmarkTree2LastPause-8 1042375000 1034811000 -0.73% garbage.BenchmarkTree2LastPause-16 972637000 851323000 -14.25% There is also visible improvement in consumed CPU time: tree2 -heapsize=8000000000 -cpus=12 before: 248.74user 6.36system 0:52.74elapsed 483%CPU after: 229.86user 6.33system 0:51.08elapsed 462%CPU -1.66s of real time, but -18.91s of consumed CPU time

Patch Set 1 #

Patch Set 2 : diff -r 3c702dae5f50 https://go.googlecode.com/hg/ #

Patch Set 3 : diff -r 3c702dae5f50 https://go.googlecode.com/hg/ #

Patch Set 4 : diff -r 3c702dae5f50 https://go.googlecode.com/hg/ #

Created: 14 years ago

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		Unified diffs	Side-by-side diffs	Delta from patch set	Stats (+40 lines, -57 lines)			Patch
	M	src/pkg/runtime/mgc0.c	View	1 2	6 chunks	+40 lines, -57 lines	0 comments	Download

Messages

Total messages: 4

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dvyukov

Hello golang-dev@googlegroups.com, I'd like you to review this change to https://go.googlecode.com/hg/

14 years ago (2012-05-19 13:55:59 UTC) #1

dvyukov

FTR, log of running test/bench/garbage/tree2 -heapsize=8000000000 -cpus=12 BEFORE: *** built heap: 7629 MB; (290805077 objects ...

14 years ago (2012-05-19 14:02:34 UTC) #2

FTR, log of running test/bench/garbage/tree2 -heapsize=8000000000 -cpus=12

BEFORE:
*** built heap: 7629 MB; (290805077 objects * 32 bytes)
gc7(8): 1848+444+0 ms, 9506 -> 9506 MB 290815155 -> 290815153 (290815223-70)
objects, 39985(207670) handoff, 22530/123/9 yields
gc pause: 2292.620 ms; collect:        0 MB; heapsize:     9506 MB
gc8(10): 1682+394+0 ms, 9506 -> 9506 MB 290815166 -> 290815165 (290815236-71)
objects, 48350(250821) handoff, 22209/165/11 yields
gc pause: 2077.233 ms; collect:        0 MB; heapsize:     9506 MB
gc9(12): 1583+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 43776(222419) handoff, 18579/272/24 yields
gc pause: 1953.393 ms; collect:        0 MB; heapsize:     9506 MB
gc10(12): 1665+349+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 89392(429419) handoff, 35336/333/24 yields
gc pause: 2015.338 ms; collect:        0 MB; heapsize:     9506 MB
gc11(12): 1642+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 90853(436690) handoff, 36438/243/17 yields
gc pause: 2012.556 ms; collect:        0 MB; heapsize:     9506 MB
gc12(12): 1609+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 36309(194234) handoff, 15327/205/12 yields
gc pause: 1979.943 ms; collect:        0 MB; heapsize:     9506 MB
gc13(12): 1562+375+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 52900(256044) handoff, 22166/327/22 yields
gc pause: 1937.505 ms; collect:        0 MB; heapsize:     9506 MB
gc14(12): 1529+351+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 29773(164911) handoff, 12133/96/6 yields
gc pause: 1881.571 ms; collect:        0 MB; heapsize:     9506 MB
gc15(12): 1623+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 49463(260378) handoff, 20307/144/10 yields
gc pause: 1994.790 ms; collect:        0 MB; heapsize:     9506 MB
gc16(12): 1637+352+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 77748(377604) handoff, 30901/286/19 yields
gc pause: 1989.721 ms; collect:        0 MB; heapsize:     9506 MB
garbage.BenchmarkTree2Mem-12 Alloc=9968014176/9968029664 Heap=10796328664
NextGC=59808060480 Mallocs=290815249
garbage.BenchmarkTree2-12 10 198978900 ns/op
garbage.BenchmarkTree2LastPause-12 1 1989721000 ns/op
garbage.BenchmarkTree2Pause-12 16 1303487625 ns/op
garbage.BenchmarkTree2Pause5-12: 345000 131644000 1953393000 2012556000
2292620000
248.74user 6.36system 0:52.74elapsed 483%CPU (0avgtext+0avgdata
40056608maxresident)k

AFTER:
*** built heap: 7629 MB; (290805077 objects * 32 bytes)
gc7(8): 1769+245+0 ms, 9506 -> 9506 MB 290815166 -> 290815164 (290815233-69)
objects, 24874(128969) handoff, 184(402983) steal, 14367/196/4 yields
gc pause: 2014.709 ms; collect:        0 MB; heapsize:     9507 MB
gc8(10): 1628+236+0 ms, 9506 -> 9506 MB 290815177 -> 290815176 (290815246-70)
objects, 19599(92807) handoff, 351(902263) steal, 10585/327/10 yields
gc pause: 1865.282 ms; collect:        0 MB; heapsize:     9507 MB
gc9(12): 1531+218+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 27546(131117) handoff, 549(1367027) steal, 14012/743/1607 yields
gc pause: 1750.154 ms; collect:        0 MB; heapsize:     9507 MB
gc10(12): 1530+223+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 55413(281245) handoff, 766(1870244) steal, 23980/475/15 yields
gc pause: 1754.019 ms; collect:        0 MB; heapsize:     9507 MB
gc11(12): 1559+230+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 57997(279389) handoff, 907(2288474) steal, 26079/779/28 yields
gc pause: 1789.805 ms; collect:        0 MB; heapsize:     9507 MB
gc12(12): 1518+224+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 30653(154882) handoff, 1080(2735051) steal, 15216/856/1411 yields
gc pause: 1742.951 ms; collect:        0 MB; heapsize:     9507 MB
gc13(12): 1462+232+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 24578(115897) handoff, 1258(3231391) steal, 14264/1159/3696 yields
gc pause: 1695.023 ms; collect:        0 MB; heapsize:     9507 MB
gc14(12): 1485+247+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 33227(161523) handoff, 1434(3539513) steal, 17393/1216/3693 yields
gc pause: 1733.579 ms; collect:        0 MB; heapsize:     9507 MB
gc15(12): 1553+230+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 36256(166940) handoff, 1631(3977215) steal, 19195/1356/3691 yields
gc pause: 1784.037 ms; collect:        0 MB; heapsize:     9507 MB
gc16(12): 1538+230+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 31168(150588) handoff, 1805(4389393) steal, 17589/1423/3691 yields
gc pause: 1769.606 ms; collect:        0 MB; heapsize:     9507 MB
garbage.BenchmarkTree2Mem-12 Alloc=9968574656/9968590064 Heap=10796328664
NextGC=59811423360 Mallocs=290815259
garbage.BenchmarkTree2-12 10 176967900 ns/op
garbage.BenchmarkTree2LastPause-12 1 1769606000 ns/op
garbage.BenchmarkTree2Pause-12 16 1165969750 ns/op
garbage.BenchmarkTree2Pause5-12: 328000 122911000 1742951000 1784037000
2014709000
229.86user 6.33system 0:51.08elapsed 462%CPU (0avgtext+0avgdata
40057824maxresident)k

---

Some lines in comparison:
gc10(12): 1665+349+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 89392(429419) handoff, 35336/333/24 yields
gc10(12): 1530+223+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 55413(281245) handoff, 766(1870244) steal, 23980/475/15 yields

gc13(12): 1562+375+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 52900(256044) handoff, 22166/327/22 yields
gc13(12): 1462+232+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 24578(115897) handoff, 1258(3231391) steal, 14264/1159/3696 yields

dvyukov

FTR, log of running test/bench/garbage/tree2 -heapsize=8000000000 -cpus=12 BEFORE: *** built heap: 7629 MB; (290805077 objects ...

14 years ago (2012-05-19 14:03:31 UTC) #3

FTR, log of running test/bench/garbage/tree2 -heapsize=8000000000 -cpus=12

BEFORE:
*** built heap: 7629 MB; (290805077 objects * 32 bytes)
gc7(8): 1848+444+0 ms, 9506 -> 9506 MB 290815155 -> 290815153 (290815223-70)
objects, 39985(207670) handoff, 22530/123/9 yields
gc pause: 2292.620 ms; collect:        0 MB; heapsize:     9506 MB
gc8(10): 1682+394+0 ms, 9506 -> 9506 MB 290815166 -> 290815165 (290815236-71)
objects, 48350(250821) handoff, 22209/165/11 yields
gc pause: 2077.233 ms; collect:        0 MB; heapsize:     9506 MB
gc9(12): 1583+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 43776(222419) handoff, 18579/272/24 yields
gc pause: 1953.393 ms; collect:        0 MB; heapsize:     9506 MB
gc10(12): 1665+349+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 89392(429419) handoff, 35336/333/24 yields
gc pause: 2015.338 ms; collect:        0 MB; heapsize:     9506 MB
gc11(12): 1642+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 90853(436690) handoff, 36438/243/17 yields
gc pause: 2012.556 ms; collect:        0 MB; heapsize:     9506 MB
gc12(12): 1609+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 36309(194234) handoff, 15327/205/12 yields
gc pause: 1979.943 ms; collect:        0 MB; heapsize:     9506 MB
gc13(12): 1562+375+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 52900(256044) handoff, 22166/327/22 yields
gc pause: 1937.505 ms; collect:        0 MB; heapsize:     9506 MB
gc14(12): 1529+351+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 29773(164911) handoff, 12133/96/6 yields
gc pause: 1881.571 ms; collect:        0 MB; heapsize:     9506 MB
gc15(12): 1623+370+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 49463(260378) handoff, 20307/144/10 yields
gc pause: 1994.790 ms; collect:        0 MB; heapsize:     9506 MB
gc16(12): 1637+352+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 77748(377604) handoff, 30901/286/19 yields
gc pause: 1989.721 ms; collect:        0 MB; heapsize:     9506 MB
garbage.BenchmarkTree2Mem-12 Alloc=9968014176/9968029664 Heap=10796328664
NextGC=59808060480 Mallocs=290815249
garbage.BenchmarkTree2-12 10 198978900 ns/op
garbage.BenchmarkTree2LastPause-12 1 1989721000 ns/op
garbage.BenchmarkTree2Pause-12 16 1303487625 ns/op
garbage.BenchmarkTree2Pause5-12: 345000 131644000 1953393000 2012556000
2292620000
248.74user 6.36system 0:52.74elapsed 483%CPU (0avgtext+0avgdata
40056608maxresident)k

AFTER:
*** built heap: 7629 MB; (290805077 objects * 32 bytes)
gc7(8): 1769+245+0 ms, 9506 -> 9506 MB 290815166 -> 290815164 (290815233-69)
objects, 24874(128969) handoff, 184(402983) steal, 14367/196/4 yields
gc pause: 2014.709 ms; collect:        0 MB; heapsize:     9507 MB
gc8(10): 1628+236+0 ms, 9506 -> 9506 MB 290815177 -> 290815176 (290815246-70)
objects, 19599(92807) handoff, 351(902263) steal, 10585/327/10 yields
gc pause: 1865.282 ms; collect:        0 MB; heapsize:     9507 MB
gc9(12): 1531+218+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 27546(131117) handoff, 549(1367027) steal, 14012/743/1607 yields
gc pause: 1750.154 ms; collect:        0 MB; heapsize:     9507 MB
gc10(12): 1530+223+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 55413(281245) handoff, 766(1870244) steal, 23980/475/15 yields
gc pause: 1754.019 ms; collect:        0 MB; heapsize:     9507 MB
gc11(12): 1559+230+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 57997(279389) handoff, 907(2288474) steal, 26079/779/28 yields
gc pause: 1789.805 ms; collect:        0 MB; heapsize:     9507 MB
gc12(12): 1518+224+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 30653(154882) handoff, 1080(2735051) steal, 15216/856/1411 yields
gc pause: 1742.951 ms; collect:        0 MB; heapsize:     9507 MB
gc13(12): 1462+232+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 24578(115897) handoff, 1258(3231391) steal, 14264/1159/3696 yields
gc pause: 1695.023 ms; collect:        0 MB; heapsize:     9507 MB
gc14(12): 1485+247+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 33227(161523) handoff, 1434(3539513) steal, 17393/1216/3693 yields
gc pause: 1733.579 ms; collect:        0 MB; heapsize:     9507 MB
gc15(12): 1553+230+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 36256(166940) handoff, 1631(3977215) steal, 19195/1356/3691 yields
gc pause: 1784.037 ms; collect:        0 MB; heapsize:     9507 MB
gc16(12): 1538+230+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 31168(150588) handoff, 1805(4389393) steal, 17589/1423/3691 yields
gc pause: 1769.606 ms; collect:        0 MB; heapsize:     9507 MB
garbage.BenchmarkTree2Mem-12 Alloc=9968574656/9968590064 Heap=10796328664
NextGC=59811423360 Mallocs=290815259
garbage.BenchmarkTree2-12 10 176967900 ns/op
garbage.BenchmarkTree2LastPause-12 1 1769606000 ns/op
garbage.BenchmarkTree2Pause-12 16 1165969750 ns/op
garbage.BenchmarkTree2Pause5-12: 328000 122911000 1742951000 1784037000
2014709000
229.86user 6.33system 0:51.08elapsed 462%CPU (0avgtext+0avgdata
40057824maxresident)k

---

Some lines in comparison:
gc10(12): 1665+349+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 89392(429419) handoff, 35336/333/24 yields
gc10(12): 1530+223+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 55413(281245) handoff, 766(1870244) steal, 23980/475/15 yields

gc13(12): 1562+375+0 ms, 9506 -> 9506 MB 290815177 -> 290815177 (290815248-71)
objects, 52900(256044) handoff, 22166/327/22 yields
gc13(12): 1462+232+0 ms, 9506 -> 9506 MB 290815188 -> 290815188 (290815258-70)
objects, 24578(115897) handoff, 1258(3231391) steal, 14264/1159/3696 yields

rsc

14 years ago (2012-05-22 17:35:57 UTC) #4

*** Submitted as http://code.google.com/p/go/source/detail?r=4f0a49b9d0c9 ***

runtime: faster GC sweep phase
benchmark                              old ns/op    new ns/op    delta

garbage.BenchmarkParser               3731065750   3715543750   -0.41%
garbage.BenchmarkParser-2             3631299750   3495248500   -3.75%
garbage.BenchmarkParser-4             3386486000   3339353000   -1.39%
garbage.BenchmarkParser-8             3267632000   3286422500   +0.58%
garbage.BenchmarkParser-16            3299203000   3316081750   +0.51%

garbage.BenchmarkTree                  977532888    919453833   -5.94%
garbage.BenchmarkTree-2                919948555    853478000   -7.23%
garbage.BenchmarkTree-4                841329000    790207000   -6.08%
garbage.BenchmarkTree-8                787792777    740380666   -6.01%
garbage.BenchmarkTree-16               899257166    846594555   -5.86%

garbage.BenchmarkTree2                 574876300    571885800   -0.52%
garbage.BenchmarkTree2-2               348162700    345888900   -0.65%
garbage.BenchmarkTree2-4               184912500    179137000   -3.22%
garbage.BenchmarkTree2-8               104243900    103485600   -0.73%
garbage.BenchmarkTree2-16               97269500     85137100  -14.25%

garbage.BenchmarkParserPause           141101976    157746974  +11.80%
garbage.BenchmarkParserPause-2         103096051     83043048  -19.45%
garbage.BenchmarkParserPause-4          52153133     45951111  -11.89%
garbage.BenchmarkParserPause-8          36730190     38901024   +5.91%
garbage.BenchmarkParserPause-16         32678875     29578585   -9.49%

garbage.BenchmarkTreePause              29487065     29648439   +0.55%
garbage.BenchmarkTreePause-2            22443494     21306159   -5.07%
garbage.BenchmarkTreePause-4            15799691     14985647   -5.15%
garbage.BenchmarkTreePause-8            10768112     9531420   -12.97%
garbage.BenchmarkTreePause-16           16329891     15205158   -6.89%

garbage.BenchmarkTree2Pause           2586957240   2577533200   -0.36%
garbage.BenchmarkTree2Pause-2         1683383760   1673923800   -0.56%
garbage.BenchmarkTree2Pause-4         1102860320   1074040280   -2.68%
garbage.BenchmarkTree2Pause-8          902627920    886122400   -1.86%
garbage.BenchmarkTree2Pause-16         856470920    804152320   -6.50%

garbage.BenchmarkParserLastPause       277316000    280839000   +1.25%
garbage.BenchmarkParserLastPause-2     179446000    163687000   -8.78%
garbage.BenchmarkParserLastPause-4     106752000     94144000  -11.81%
garbage.BenchmarkParserLastPause-8      57758000     61640000   +6.72%
garbage.BenchmarkParserLastPause-16     51235000     42552000  -16.95%

garbage.BenchmarkTreeLastPause          45244000     50786000  +12.25%
garbage.BenchmarkTreeLastPause-2        37163000     34654000   -6.75%
garbage.BenchmarkTreeLastPause-4        24178000     21967000   -9.14%
garbage.BenchmarkTreeLastPause-8        20390000     15648000  -30.30%
garbage.BenchmarkTreeLastPause-16       22398000     20180000   -9.90%

garbage.BenchmarkTree2LastPause       5748706000   5718809000   -0.52%
garbage.BenchmarkTree2LastPause-2     3481570000   3458844000   -0.65%
garbage.BenchmarkTree2LastPause-4     1849073000   1791330000   -3.22%
garbage.BenchmarkTree2LastPause-8     1042375000   1034811000   -0.73%
garbage.BenchmarkTree2LastPause-16     972637000    851323000  -14.25%

There is also visible improvement in consumed CPU time:
tree2 -heapsize=8000000000 -cpus=12
before: 248.74user 6.36system 0:52.74elapsed 483%CPU
after:  229.86user 6.33system 0:51.08elapsed 462%CPU
-1.66s of real time, but -18.91s of consumed CPU time

R=golang-dev
CC=golang-dev
http://codereview.appspot.com/6215065

Committer: Russ Cox <rsc@golang.org>

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