(1) Count pointer-free objects found during scanning roots
as marked bytes, by not zeroing the mark total after scanning roots.
(2) Don't count the bytes for the roots themselves, by not adding
them to the mark total in scanblock (the zeroing removed by (1)
was aimed at that add but hitting more).
Combined, (1) and (2) fix the calculation of the marked heap size.
This makes the GC trigger much less often in the Go 1 benchmarks,
which have a global []byte pointing at 256 MB of data.
That 256 MB allocation was not being included in the heap size
in the current code, but was included in Go 1.4.
This is the source of much of the relative slowdown in that directory.
(3) Count the bytes for the roots as scanned work, by not zeroing
the scan total after scanning roots. There is no strict justification
for this, and it probably doesn't matter much either way,
but it was always combined with another buggy zeroing
(removed in (1)), so guilty by association.
Austin noticed this.
name old mean new mean delta
BenchmarkBinaryTree17 13.1s × (0.97,1.03) 5.9s × (0.97,1.05) -55.19% (p=0.000)
BenchmarkFannkuch11 4.35s × (0.99,1.01) 4.37s × (1.00,1.01) +0.47% (p=0.032)
BenchmarkFmtFprintfEmpty 84.6ns × (0.95,1.14) 85.7ns × (0.94,1.05) ~ (p=0.521)
BenchmarkFmtFprintfString 320ns × (0.95,1.06) 283ns × (0.99,1.02) -11.48% (p=0.000)
BenchmarkFmtFprintfInt 311ns × (0.98,1.03) 288ns × (0.99,1.02) -7.26% (p=0.000)
BenchmarkFmtFprintfIntInt 554ns × (0.96,1.05) 478ns × (0.99,1.02) -13.70% (p=0.000)
BenchmarkFmtFprintfPrefixedInt 434ns × (0.96,1.06) 393ns × (0.98,1.04) -9.60% (p=0.000)
BenchmarkFmtFprintfFloat 620ns × (0.99,1.03) 584ns × (0.99,1.01) -5.73% (p=0.000)
BenchmarkFmtManyArgs 2.19µs × (0.98,1.03) 1.94µs × (0.99,1.01) -11.62% (p=0.000)
BenchmarkGobDecode 21.2ms × (0.97,1.06) 15.2ms × (0.99,1.01) -28.17% (p=0.000)
BenchmarkGobEncode 18.1ms × (0.94,1.06) 11.8ms × (0.99,1.01) -35.00% (p=0.000)
BenchmarkGzip 650ms × (0.98,1.01) 649ms × (0.99,1.02) ~ (p=0.802)
BenchmarkGunzip 143ms × (1.00,1.01) 143ms × (1.00,1.01) ~ (p=0.438)
BenchmarkHTTPClientServer 110µs × (0.98,1.04) 101µs × (0.98,1.02) -8.79% (p=0.000)
BenchmarkJSONEncode 40.3ms × (0.97,1.03) 31.8ms × (0.98,1.03) -20.92% (p=0.000)
BenchmarkJSONDecode 119ms × (0.97,1.02) 108ms × (0.99,1.02) -9.15% (p=0.000)
BenchmarkMandelbrot200 6.03ms × (1.00,1.01) 6.03ms × (0.99,1.01) ~ (p=0.750)
BenchmarkGoParse 8.58ms × (0.89,1.10) 6.80ms × (1.00,1.00) -20.71% (p=0.000)
BenchmarkRegexpMatchEasy0_32 162ns × (1.00,1.01) 162ns × (0.99,1.02) ~ (p=0.131)
BenchmarkRegexpMatchEasy0_1K 540ns × (0.99,1.02) 559ns × (0.99,1.02) +3.58% (p=0.000)
BenchmarkRegexpMatchEasy1_32 139ns × (0.98,1.04) 139ns × (1.00,1.00) ~ (p=0.466)
BenchmarkRegexpMatchEasy1_1K 889ns × (0.99,1.01) 885ns × (0.99,1.01) -0.50% (p=0.022)
BenchmarkRegexpMatchMedium_32 252ns × (0.99,1.02) 252ns × (0.99,1.01) ~ (p=0.469)
BenchmarkRegexpMatchMedium_1K 72.9µs × (0.99,1.01) 73.6µs × (0.99,1.03) ~ (p=0.168)
BenchmarkRegexpMatchHard_32 3.87µs × (1.00,1.01) 3.86µs × (1.00,1.00) ~ (p=0.055)
BenchmarkRegexpMatchHard_1K 118µs × (0.99,1.01) 117µs × (0.99,1.00) ~ (p=0.133)
BenchmarkRevcomp 995ms × (0.94,1.10) 949ms × (0.99,1.01) -4.64% (p=0.000)
BenchmarkTemplate 141ms × (0.97,1.02) 127ms × (0.99,1.01) -10.00% (p=0.000)
BenchmarkTimeParse 641ns × (0.99,1.01) 623ns × (0.99,1.01) -2.79% (p=0.000)
BenchmarkTimeFormat 729ns × (0.98,1.03) 679ns × (0.99,1.00) -6.93% (p=0.000)
Change-Id: I839bd7356630d18377989a0748763414e15ed057
Reviewed-on: https://go-review.googlesource.com/9602
Reviewed-by: Austin Clements <austin@google.com>
}
}
- // Root aren't part of the heap, so don't count them toward
- // marked heap bytes.
- gcw.bytesMarked = 0
- gcw.scanWork = 0
gcw.dispose()
}
}
gcw := &getg().m.p.ptr().gcw
- origBytesMarked := gcw.bytesMarked
- origScanWork := gcw.scanWork
scanframe := func(frame *stkframe, unused unsafe.Pointer) bool {
// Pick up gcw as free variable so gentraceback and friends can
// keep the same signature.
}
gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, scanframe, nil, 0)
tracebackdefers(gp, scanframe, nil)
- // Stacks aren't part of the heap, so don't count them toward
- // marked heap bytes.
- gcw.bytesMarked = origBytesMarked
- gcw.scanWork = origScanWork
if gcphase == _GCmarktermination {
gcw.dispose()
}
}
}
- gcw.bytesMarked += uint64(n)
gcw.scanWork += scanWork
}