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The Go programming language
38f674687a
Currently we always zero objects when we allocate them. We used to have an optimization that would not zero objects that had not been allocated since the whole span was last zeroed (either by getting it from the system or by getting it from the heap, which does a bulk zero), but this depended on the sweeper clobbering the first two words of each object. Hence, we lost this optimization when the bitmap sweeper went away. Re-introduce this optimization using a different mechanism. Each span already keeps a flag indicating that it just came from the OS or was just bulk zeroed by the mheap. We can simply use this flag to know when we don't need to zero an object. This is slightly less efficient than the old optimization: if a span gets allocated and partially used, then GC happens and the span gets returned to the mcentral, then the span gets re-acquired, the old optimization knew that it only had to re-zero the objects that had been reclaimed, whereas this optimization will re-zero everything. However, in this case, you're already paying for the garbage collection, and you've only wasted one zeroing of the span, so in practice there seems to be little difference. (If we did want to revive the full optimization, each span could keep track of a frontier beyond which all free slots are zeroed. I prototyped this and it didn't obvious do any better than the much simpler approach in this commit.) This significantly improves BinaryTree17, which is allocation-heavy (and runs first, so most pages are already zeroed), and slightly improves everything else. name old time/op new time/op delta XBenchGarbage-12 2.15ms ± 1% 2.14ms ± 1% -0.80% (p=0.000 n=17+17) name old time/op new time/op delta BinaryTree17-12 2.71s ± 1% 2.56s ± 1% -5.73% (p=0.000 n=18+19) DivconstI64-12 1.70ns ± 1% 1.70ns ± 1% ~ (p=0.562 n=18+18) DivconstU64-12 1.74ns ± 2% 1.74ns ± 1% ~ (p=0.394 n=20+20) DivconstI32-12 1.74ns ± 0% 1.74ns ± 0% ~ (all samples are equal) DivconstU32-12 1.66ns ± 1% 1.66ns ± 0% ~ (p=0.516 n=15+16) DivconstI16-12 1.84ns ± 0% 1.84ns ± 0% ~ (all samples are equal) DivconstU16-12 1.82ns ± 0% 1.82ns ± 0% ~ (all samples are equal) DivconstI8-12 1.79ns ± 0% 1.79ns ± 0% ~ (all samples are equal) DivconstU8-12 1.60ns ± 0% 1.60ns ± 1% ~ (p=0.603 n=17+19) Fannkuch11-12 2.11s ± 1% 2.11s ± 0% ~ (p=0.333 n=16+19) FmtFprintfEmpty-12 45.1ns ± 4% 45.4ns ± 5% ~ (p=0.111 n=20+20) FmtFprintfString-12 134ns ± 0% 129ns ± 0% -3.45% (p=0.000 n=18+16) FmtFprintfInt-12 131ns ± 1% 129ns ± 1% -1.54% (p=0.000 n=16+18) FmtFprintfIntInt-12 205ns ± 2% 203ns ± 0% -0.56% (p=0.014 n=20+18) FmtFprintfPrefixedInt-12 200ns ± 2% 197ns ± 1% -1.48% (p=0.000 n=20+18) FmtFprintfFloat-12 256ns ± 1% 256ns ± 0% -0.21% (p=0.008 n=18+20) FmtManyArgs-12 805ns ± 0% 804ns ± 0% -0.19% (p=0.001 n=18+18) GobDecode-12 7.21ms ± 1% 7.14ms ± 1% -0.92% (p=0.000 n=19+20) GobEncode-12 5.88ms ± 1% 5.88ms ± 1% ~ (p=0.641 n=18+19) Gzip-12 218ms ± 1% 218ms ± 1% ~ (p=0.271 n=19+18) Gunzip-12 37.1ms ± 0% 36.9ms ± 0% -0.29% (p=0.000 n=18+17) HTTPClientServer-12 78.1µs ± 2% 77.4µs ± 2% ~ (p=0.070 n=19+19) JSONEncode-12 15.5ms ± 1% 15.5ms ± 0% ~ (p=0.063 n=20+18) JSONDecode-12 56.1ms ± 0% 55.4ms ± 1% -1.18% (p=0.000 n=19+18) Mandelbrot200-12 4.05ms ± 0% 4.06ms ± 0% +0.29% (p=0.001 n=18+18) GoParse-12 3.28ms ± 1% 3.21ms ± 1% -2.30% (p=0.000 n=20+20) RegexpMatchEasy0_32-12 69.4ns ± 2% 69.3ns ± 1% ~ (p=0.205 n=18+16) RegexpMatchEasy0_1K-12 239ns ± 0% 239ns ± 0% ~ (all samples are equal) RegexpMatchEasy1_32-12 69.4ns ± 1% 69.4ns ± 1% ~ (p=0.620 n=15+18) RegexpMatchEasy1_1K-12 370ns ± 1% 369ns ± 2% ~ (p=0.088 n=20+20) RegexpMatchMedium_32-12 108ns ± 0% 108ns ± 0% ~ (all samples are equal) RegexpMatchMedium_1K-12 33.6µs ± 3% 33.5µs ± 3% ~ (p=0.718 n=20+20) RegexpMatchHard_32-12 1.68µs ± 1% 1.67µs ± 2% ~ (p=0.316 n=20+20) RegexpMatchHard_1K-12 50.5µs ± 3% 50.4µs ± 3% ~ (p=0.659 n=20+20) Revcomp-12 381ms ± 1% 381ms ± 1% ~ (p=0.916 n=19+18) Template-12 66.5ms ± 1% 65.8ms ± 2% -1.08% (p=0.000 n=20+20) TimeParse-12 317ns ± 0% 319ns ± 0% +0.48% (p=0.000 n=19+12) TimeFormat-12 338ns ± 0% 338ns ± 0% ~ (p=0.124 n=19+18) [Geo mean] 5.99µs 5.96µs -0.54% Change-Id: I638ffd9d9f178835bbfa499bac20bd7224f1a907 Reviewed-on: https://go-review.googlesource.com/22591 Reviewed-by: Rick Hudson <rlh@golang.org> |
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The Go Programming Language
Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.
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--
Binary Distribution Notes
If you have just untarred a binary Go distribution, you need to set the environment variable $GOROOT to the full path of the go directory (the one containing this file). You can omit the variable if you unpack it into /usr/local/go, or if you rebuild from sources by running all.bash (see doc/install-source.html). You should also add the Go binary directory $GOROOT/bin to your shell's path.
For example, if you extracted the tar file into $HOME/go, you might put the following in your .profile:
export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin
See https://golang.org/doc/install or doc/install.html for more details.