From 8e25d4ccef45860186187d4ca7428052028abbb0 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Thu, 2 Jun 2016 11:09:20 -0400 Subject: [PATCH] runtime: eliminate heapBitsSetTypeNoScan MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit It's no longer necessary to maintain the bitmap of noscan objects since we now use the span metadata to determine that they're noscan instead of the bitmap. The combined effect of segregating noscan spans and the follow-on optimizations is roughly a 1% improvement in performance across the go1 benchmarks and the x/benchmarks, with no increase in heap size. Benchmark details: https://perf.golang.org/search?q=upload:20170420.1 name old time/op new time/op delta Garbage/benchmem-MB=64-12 2.27ms ± 0% 2.25ms ± 1% -0.96% (p=0.000 n=15+18) name old time/op new time/op delta BinaryTree17-12 2.53s ± 2% 2.55s ± 1% +0.68% (p=0.001 n=17+16) Fannkuch11-12 3.02s ± 0% 3.01s ± 0% -0.15% (p=0.000 n=16+16) FmtFprintfEmpty-12 47.1ns ± 7% 47.0ns ± 5% ~ (p=0.886 n=20+17) FmtFprintfString-12 73.6ns ± 3% 73.8ns ± 1% +0.30% (p=0.026 n=19+17) FmtFprintfInt-12 80.3ns ± 2% 80.2ns ± 1% ~ (p=0.994 n=20+18) FmtFprintfIntInt-12 124ns ± 0% 124ns ± 0% ~ (all samples are equal) FmtFprintfPrefixedInt-12 172ns ± 1% 171ns ± 1% -0.72% (p=0.003 n=20+18) FmtFprintfFloat-12 217ns ± 1% 216ns ± 1% -0.27% (p=0.019 n=18+19) FmtManyArgs-12 490ns ± 1% 488ns ± 0% -0.36% (p=0.014 n=18+18) GobDecode-12 6.71ms ± 1% 6.73ms ± 1% +0.42% (p=0.000 n=20+20) GobEncode-12 5.25ms ± 0% 5.24ms ± 0% -0.20% (p=0.001 n=18+20) Gzip-12 227ms ± 0% 226ms ± 1% ~ (p=0.107 n=20+19) Gunzip-12 38.8ms ± 0% 38.8ms ± 0% ~ (p=0.221 n=19+18) HTTPClientServer-12 75.4µs ± 1% 76.3µs ± 1% +1.26% (p=0.000 n=20+19) JSONEncode-12 14.7ms ± 0% 14.7ms ± 1% -0.14% (p=0.002 n=18+17) JSONDecode-12 57.6ms ± 0% 55.2ms ± 0% -4.13% (p=0.000 n=19+19) Mandelbrot200-12 3.73ms ± 0% 3.73ms ± 0% -0.09% (p=0.000 n=19+17) GoParse-12 3.18ms ± 1% 3.15ms ± 1% -0.90% (p=0.000 n=18+20) RegexpMatchEasy0_32-12 73.3ns ± 2% 73.2ns ± 1% ~ (p=0.994 n=20+18) RegexpMatchEasy0_1K-12 236ns ± 2% 234ns ± 1% -0.70% (p=0.002 n=19+17) RegexpMatchEasy1_32-12 69.7ns ± 2% 69.9ns ± 2% ~ (p=0.416 n=20+20) RegexpMatchEasy1_1K-12 366ns ± 1% 365ns ± 1% ~ (p=0.376 n=19+17) RegexpMatchMedium_32-12 109ns ± 1% 108ns ± 1% ~ (p=0.461 n=17+18) RegexpMatchMedium_1K-12 35.2µs ± 1% 35.2µs ± 3% ~ (p=0.238 n=19+20) RegexpMatchHard_32-12 1.77µs ± 1% 1.77µs ± 1% +0.33% (p=0.007 n=17+16) RegexpMatchHard_1K-12 53.2µs ± 0% 53.3µs ± 0% +0.26% (p=0.001 n=17+17) Revcomp-12 1.13s ±117% 0.87s ±184% ~ (p=0.813 n=20+19) Template-12 63.9ms ± 1% 64.6ms ± 1% +1.18% (p=0.000 n=19+20) TimeParse-12 313ns ± 5% 312ns ± 0% ~ (p=0.114 n=20+19) TimeFormat-12 336ns ± 0% 333ns ± 0% -0.97% (p=0.000 n=18+16) [Geo mean] 50.6µs 50.1µs -1.04% This is a cherry-pick of dev.garbage commit edb54c300f, with updated benchmark results. Change-Id: Ic77faaa15cdac3bfbbb0032dde5c204e05a0fd8e Reviewed-on: https://go-review.googlesource.com/41253 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Rick Hudson --- src/runtime/malloc.go | 4 +--- src/runtime/mbitmap.go | 12 +++++------- 2 files changed, 6 insertions(+), 10 deletions(-) diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go index db5df37868..ea0d585ed9 100644 --- a/src/runtime/malloc.go +++ b/src/runtime/malloc.go @@ -703,9 +703,7 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer { } var scanSize uintptr - if noscan { - heapBitsSetTypeNoScan(uintptr(x)) - } else { + if !noscan { // If allocating a defer+arg block, now that we've picked a malloc size // large enough to hold everything, cut the "asked for" size down to // just the defer header, so that the GC bitmap will record the arg block diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go index 48754de562..ef36fb8575 100644 --- a/src/runtime/mbitmap.go +++ b/src/runtime/mbitmap.go @@ -45,6 +45,11 @@ // not checkmarked, and is the dead encoding. // These properties must be preserved when modifying the encoding. // +// The bitmap for noscan spans is not maintained. Code must ensure +// that an object is scannable before consulting its bitmap by +// checking either the noscan bit in the span or by consulting its +// type's information. +// // Checkmarks // // In a concurrent garbage collector, one worries about failing to mark @@ -1319,13 +1324,6 @@ Phase4: } } -// heapBitsSetTypeNoScan marks x as noscan by setting the first word -// of x in the heap bitmap to scalar/dead. -func heapBitsSetTypeNoScan(x uintptr) { - h := heapBitsForAddr(uintptr(x)) - *h.bitp &^= (bitPointer | bitScan) << h.shift -} - var debugPtrmask struct { lock mutex data *byte -- 2.48.1