b49b71ae19
Currently the runtime rescans globals during mark 2 and mark termination. This costs as much as 500µs/MB in STW time, which is enough to surpass the 10ms STW limit with only 20MB of globals. It's also basically unnecessary. The compiler already generates write barriers for global -> heap pointer updates and the regular write barrier doesn't check whether the slot is a global or in the heap. Some less common write barriers do cause problems. heapBitsBulkBarrier, which is used by typedmemmove and related functions, currently depends on having access to the pointer bitmap and as a result ignores writes to globals. Likewise, the reflect-related write barriers reflect_typedmemmovepartial and callwritebarrier ignore non-heap destinations; though it appears they can never be called with global pointers anyway. This commit makes heapBitsBulkBarrier issue write barriers for writes to global pointers using the data and BSS pointer bitmaps, removes the inheap checks from the reflection write barriers, and eliminates the rescans during mark 2 and mark termination. It also adds a test that writes to globals have write barriers. Programs with large data+BSS segments (with pointers) aren't common, but for programs that do have large data+BSS segments, this significantly reduces pause time: name \ 95%ile-time/markTerm old new delta LargeBSS/bss:1GB/gomaxprocs:4 148200µs ± 6% 302µs ±52% -99.80% (p=0.008 n=5+5) This very slightly improves the go1 benchmarks: name old time/op new time/op delta BinaryTree17-12 2.62s ± 3% 2.62s ± 4% ~ (p=0.904 n=20+20) Fannkuch11-12 2.15s ± 1% 2.13s ± 0% -1.29% (p=0.000 n=18+20) FmtFprintfEmpty-12 48.3ns ± 2% 47.6ns ± 1% -1.52% (p=0.000 n=20+16) FmtFprintfString-12 152ns ± 0% 152ns ± 1% ~ (p=0.725 n=18+18) FmtFprintfInt-12 150ns ± 1% 149ns ± 1% -1.14% (p=0.000 n=19+20) FmtFprintfIntInt-12 250ns ± 0% 244ns ± 1% -2.12% (p=0.000 n=20+18) FmtFprintfPrefixedInt-12 219ns ± 1% 217ns ± 1% -1.20% (p=0.000 n=19+20) FmtFprintfFloat-12 280ns ± 0% 281ns ± 1% +0.47% (p=0.000 n=19+19) FmtManyArgs-12 928ns ± 0% 923ns ± 1% -0.53% (p=0.000 n=19+18) GobDecode-12 7.21ms ± 1% 7.24ms ± 2% ~ (p=0.091 n=19+19) GobEncode-12 6.07ms ± 1% 6.05ms ± 1% -0.36% (p=0.002 n=20+17) Gzip-12 265ms ± 1% 265ms ± 1% ~ (p=0.496 n=20+19) Gunzip-12 39.6ms ± 1% 39.3ms ± 1% -0.85% (p=0.000 n=19+19) HTTPClientServer-12 74.0µs ± 2% 73.8µs ± 1% ~ (p=0.569 n=20+19) JSONEncode-12 15.4ms ± 1% 15.3ms ± 1% -0.25% (p=0.049 n=17+17) JSONDecode-12 53.7ms ± 2% 53.0ms ± 1% -1.29% (p=0.000 n=18+17) Mandelbrot200-12 3.97ms ± 1% 3.97ms ± 0% ~ (p=0.072 n=17+18) GoParse-12 3.35ms ± 2% 3.36ms ± 1% +0.51% (p=0.005 n=18+20) RegexpMatchEasy0_32-12 72.7ns ± 2% 72.2ns ± 1% -0.70% (p=0.005 n=19+19) RegexpMatchEasy0_1K-12 246ns ± 1% 245ns ± 0% -0.60% (p=0.000 n=18+16) RegexpMatchEasy1_32-12 72.8ns ± 1% 72.5ns ± 1% -0.37% (p=0.011 n=18+18) RegexpMatchEasy1_1K-12 380ns ± 1% 385ns ± 1% +1.34% (p=0.000 n=20+19) RegexpMatchMedium_32-12 115ns ± 2% 115ns ± 1% +0.44% (p=0.047 n=20+20) RegexpMatchMedium_1K-12 35.4µs ± 1% 35.5µs ± 1% ~ (p=0.079 n=18+19) RegexpMatchHard_32-12 1.83µs ± 0% 1.80µs ± 1% -1.76% (p=0.000 n=18+18) RegexpMatchHard_1K-12 55.1µs ± 0% 54.3µs ± 1% -1.42% (p=0.000 n=18+19) Revcomp-12 386ms ± 1% 381ms ± 1% -1.14% (p=0.000 n=18+18) Template-12 61.5ms ± 2% 61.5ms ± 2% ~ (p=0.647 n=19+20) TimeParse-12 338ns ± 0% 336ns ± 1% -0.72% (p=0.000 n=14+19) TimeFormat-12 350ns ± 0% 357ns ± 0% +2.05% (p=0.000 n=19+18) [Geo mean] 55.3µs 55.0µs -0.41% Change-Id: I57e8720385a1b991aeebd111b6874354308e2a6b Reviewed-on: https://go-review.googlesource.com/20829 Run-TryBot: Austin Clements <austin@google.com> Reviewed-by: Rick Hudson <rlh@golang.org> |
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