runtime: garbage collection slower from go1.2 to tip #7956
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2x of this is probably just https://code.google.com/p/go/source/detail?r=234b65f69439 So runtime.GC() got slower (which now does two GCs), but not garbage collection itself that much. Actual GC probably got a bit slower due to precise GC, but not as bad as this bug report makes it look. Also, I thought (but can't recall exactly which CL) that Go 1.3 is better at using multiple CPUs during GC, but this test might be constraining it to 1. |
I've modified the program as: http://play.golang.org/p/X6ktVBSxp9 And here is gc trace: START gc17(1): 1+0+118292+0 us, 3982 -> 7965 MB, 1490930 (2490954-1000024) objects, 663379/0/0 sweeps, 0(0) handoff, 0(0) steal, 0/0/0 yields gc18(1): 1+0+117926+0 us, 3983 -> 7967 MB, 1490930 (2494938-1004008) objects, 667363/1/0 sweeps, 0(0) handoff, 0(0) steal, 0/0/0 yields END gc19(1): 1+0+118287+0 us, 3983 -> 6016 MB, 1488981 (2496973-1007992) objects, 667365/0/0 sweeps, 0(0) handoff, 0(0) steal, 0/0/0 yields gc20(1): 1+134044+118120+0 us, 3982 -> 3982 MB, 1486945 (2496973-1010028) objects, 667365/0/665413 sweeps, 0(0) handoff, 0(0) steal, 0/0/0 yields gc time: 372.813836ms So while runtime.GC time is 372ms, actual GC pause when triggered normally is 118ms, which is slightly better than 1.2. However, the pause in 1.3 does not include sweeping, so it seems that total GC time is still somewhat worser than in 1.2. I've looked at the profile, and I do not see anything pathological there, or anything we can easily fix for 1.3: 65.40% gc gc [.] runtime.memclr 8.77% gc gc [.] markonly 8.37% gc gc [.] runtime.MSpan_Sweep 2.47% gc gc [.] scanblock 2.10% gc gc [.] runtime.memmove 2.05% gc gc [.] strings.Repeat 1.27% gc [kernel.kallsyms] [k] clear_page_c 1.23% gc gc [.] runtime.sweepone 1.03% gc gc [.] runtime.updatememstats 0.75% gc gc [.] markroot We know that we need to improve GC, and there are plans to do some work for 1.4. I do not see anything actionable for 1.3, so marking this as #WontFix. Status changed to WontFix. |
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$ cat junk.go package main import ( "fmt" "runtime" "strconv" "strings" "time" ) func main() { m := make(map[string]string, 1e6) for i := 0; i < 1e6; i++ { m[strconv.Itoa(i)] = strings.Repeat("abcd", 1024) } runtime.GC() runtime.GC() start := time.Now() runtime.GC() gctime := time.Since(start) fmt.Printf("gc time: %s\n", gctime) fmt.Printf("%d\n", len(m)) } $ go version go version go1.2 linux/amd64 $ GOMAXPROCS=1 go run junk.go gc time: 147.169988ms 1000000 $ go version go version devel +d797b2316601 Tue May 06 09:12:15 2014 -0400 + linux/amd64 $ GOMAXPROCS=1 go run junk.go gc time: 410.553639ms 1000000The text was updated successfully, but these errors were encountered: