a20fd1f6ba
With the switch to separate mark bitmaps, the scan/dead bit for the first word of each object is now unused. Reclaim this bit and use it as a scan/dead bit, just like words three and on. The second word is still used for checkmark. This dramatically simplifies heapBitsSetTypeNoScan and hasPointers, since they no longer need different cases for 1, 2, and 3+ word objects. They can instead just manipulate the heap bitmap for the first word and be done with it. In order to enable this, we change heapBitsSetType and runGCProg to always set the scan/dead bit to scan for the first word on every code path. Since these functions only apply to types that have pointers, there's no need to do this conditionally: it's *always* necessary to set the scan bit in the first word. We also change every place that scans an object and checks if there are more pointers. Rather than only checking morePointers if the word is >= 2, we now check morePointers if word != 1 (since that's the checkmark word). Looking forward, we should probably reclaim the checkmark bit, too, but that's going to be quite a bit more work. Tested by setting doubleCheck in heapBitsSetType and running all.bash on both linux/amd64 and linux/386, and by running GOGC=10 all.bash. This particularly improves the FmtFprintf* go1 benchmarks, since they do a large amount of noscan allocation. name old time/op new time/op delta BinaryTree17-12 2.34s ± 1% 2.38s ± 1% +1.70% (p=0.000 n=17+19) Fannkuch11-12 2.09s ± 0% 2.09s ± 1% ~ (p=0.276 n=17+16) FmtFprintfEmpty-12 44.9ns ± 2% 44.8ns ± 2% ~ (p=0.340 n=19+18) FmtFprintfString-12 127ns ± 0% 125ns ± 0% -1.57% (p=0.000 n=16+15) FmtFprintfInt-12 128ns ± 0% 122ns ± 1% -4.45% (p=0.000 n=15+20) FmtFprintfIntInt-12 207ns ± 1% 193ns ± 0% -6.55% (p=0.000 n=19+14) FmtFprintfPrefixedInt-12 197ns ± 1% 191ns ± 0% -2.93% (p=0.000 n=17+18) FmtFprintfFloat-12 263ns ± 0% 248ns ± 1% -5.88% (p=0.000 n=15+19) FmtManyArgs-12 794ns ± 0% 779ns ± 1% -1.90% (p=0.000 n=18+18) GobDecode-12 7.14ms ± 2% 7.11ms ± 1% ~ (p=0.072 n=20+20) GobEncode-12 5.85ms ± 1% 5.82ms ± 1% -0.49% (p=0.000 n=20+20) Gzip-12 218ms ± 1% 215ms ± 1% -1.22% (p=0.000 n=19+19) Gunzip-12 36.8ms ± 0% 36.7ms ± 0% -0.18% (p=0.006 n=18+20) HTTPClientServer-12 77.1µs ± 4% 77.1µs ± 3% ~ (p=0.945 n=19+20) JSONEncode-12 15.6ms ± 1% 15.9ms ± 1% +1.68% (p=0.000 n=18+20) JSONDecode-12 55.2ms ± 1% 53.6ms ± 1% -2.93% (p=0.000 n=17+19) Mandelbrot200-12 4.05ms ± 1% 4.05ms ± 0% ~ (p=0.306 n=17+17) GoParse-12 3.14ms ± 1% 3.10ms ± 1% -1.31% (p=0.000 n=19+18) RegexpMatchEasy0_32-12 69.3ns ± 1% 70.0ns ± 0% +0.89% (p=0.000 n=19+17) RegexpMatchEasy0_1K-12 237ns ± 1% 236ns ± 0% -0.62% (p=0.000 n=19+16) RegexpMatchEasy1_32-12 69.5ns ± 1% 70.3ns ± 1% +1.14% (p=0.000 n=18+17) RegexpMatchEasy1_1K-12 377ns ± 1% 366ns ± 1% -3.03% (p=0.000 n=15+19) RegexpMatchMedium_32-12 107ns ± 1% 107ns ± 2% ~ (p=0.318 n=20+19) RegexpMatchMedium_1K-12 33.8µs ± 3% 33.5µs ± 1% -1.04% (p=0.001 n=20+19) RegexpMatchHard_32-12 1.68µs ± 1% 1.73µs ± 0% +2.50% (p=0.000 n=20+18) RegexpMatchHard_1K-12 50.8µs ± 1% 52.0µs ± 1% +2.50% (p=0.000 n=19+18) Revcomp-12 381ms ± 1% 385ms ± 1% +1.00% (p=0.000 n=17+18) Template-12 64.9ms ± 3% 62.6ms ± 1% -3.55% (p=0.000 n=19+18) TimeParse-12 324ns ± 0% 328ns ± 1% +1.25% (p=0.000 n=18+18) TimeFormat-12 345ns ± 0% 334ns ± 0% -3.31% (p=0.000 n=15+17) [Geo mean] 52.1µs 51.5µs -1.00% Change-Id: I13e74da3193a7f80794c654f944d1f0d60817049 Reviewed-on: https://go-review.googlesource.com/22632 Reviewed-by: Rick Hudson <rlh@golang.org> Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> |
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