> If AbstractStringBuilder only grow, the inflated value which has been encoded > in UTF16 can't be compressed. > toString() can skip compression in this case. This can save an > ArrayAllocation in StringUTF16::compress(). > > java.io.BufferedRead::readLine() is a case that StringBuilder grows only. > > In microbench, we expect to see that allocation/op reduces 20%. The initial > capacity of StringBuilder is S in bytes. When it encounters the 1st character > that can't be encoded in LATIN1, it inflates and allocate a new array of 2*S. > `toString()` will try to compress that value so it need to allocate S bytes. > The last step allocates 2*S bytes because it has to copy the string. so it > requires to allocate 5 * S bytes in total. By skipping the failed > compression, it only allocates 4 * S bytes. that's 20%. In real execution, > we observe 16% allocation reduction, tracked by JMH GC profiler > `gc.alloc.rate.norm `. I think it's because HotSpot can't track all > allocations. > > Not only allocation drops, the runtime performance(ns/op) also increases from > 3.34% to 18.91%. > > Before: > > $$make test > TEST="micro:org.openjdk.bench.java.lang.StringBuilders.toStringWithMixedChars" > MICRO="OPTIONS=-prof gc -gc true -o before.log -jvm > $HOME/Devel/jdk_baseline/bin/java" > > Benchmark > (MIXED_SIZE) Mode Cnt Score Error Units > StringBuilders.toStringWithMixedChars > 128 avgt 15 649.846 ± 76.291 ns/op > StringBuilders.toStringWithMixedChars:·gc.alloc.rate > 128 avgt 15 872.855 ± 128.259 MB/sec > StringBuilders.toStringWithMixedChars:·gc.alloc.rate.norm > 128 avgt 15 880.121 ± 0.050 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space > 128 avgt 15 707.730 ± 194.421 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space.norm > 128 avgt 15 706.602 ± 94.504 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space > 128 avgt 15 0.001 ± 0.002 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space.norm > 128 avgt 15 0.001 ± 0.001 B/op > StringBuilders.toStringWithMixedChars:·gc.count > 128 avgt 15 113.000 counts > StringBuilders.toStringWithMixedChars:·gc.time > 128 avgt 15 85.000 ms > StringBuilders.toStringWithMixedChars > 256 avgt 15 1316.652 ± 112.771 ns/op > StringBuilders.toStringWithMixedChars:·gc.alloc.rate > 256 avgt 15 800.864 ± 76.869 MB/sec > StringBuilders.toStringWithMixedChars:·gc.alloc.rate.norm > 256 avgt 15 1648.288 ± 0.162 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space > 256 avgt 15 599.736 ± 174.001 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space.norm > 256 avgt 15 1229.669 ± 318.518 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space > 256 avgt 15 0.001 ± 0.001 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space.norm > 256 avgt 15 0.001 ± 0.002 B/op > StringBuilders.toStringWithMixedChars:·gc.count > 256 avgt 15 133.000 counts > StringBuilders.toStringWithMixedChars:·gc.time > 256 avgt 15 92.000 ms > StringBuilders.toStringWithMixedChars > 1024 avgt 15 5204.303 ± 418.115 ns/op > StringBuilders.toStringWithMixedChars:·gc.alloc.rate > 1024 avgt 15 768.730 ± 72.945 MB/sec > StringBuilders.toStringWithMixedChars:·gc.alloc.rate.norm > 1024 avgt 15 6256.844 ± 0.358 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space > 1024 avgt 15 655.852 ± 121.602 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space.norm > 1024 avgt 15 5315.265 ± 578.878 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space > 1024 avgt 15 0.002 ± 0.002 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space.norm > 1024 avgt 15 0.014 ± 0.011 B/op > StringBuilders.toStringWithMixedChars:·gc.count > 1024 avgt 15 96.000 counts > StringBuilders.toStringWithMixedChars:·gc.time > 1024 avgt 15 86.000 ms > > > After > > $make test > TEST="micro:org.openjdk.bench.java.lang.StringBuilders.toStringWithMixedChars" > MICRO="OPTIONS=-prof gc -gc true -o after.log" > > Benchmark > (MIXED_SIZE) Mode Cnt Score Error Units > StringBuilders.toStringWithMixedChars > 128 avgt 15 627.522 ± 54.804 ns/op > StringBuilders.toStringWithMixedChars:·gc.alloc.rate > 128 avgt 15 751.353 ± 83.478 MB/sec > StringBuilders.toStringWithMixedChars:·gc.alloc.rate.norm > 128 avgt 15 736.120 ± 0.062 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space > 128 avgt 15 589.102 ± 164.083 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space.norm > 128 avgt 15 575.425 ± 127.021 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space > 128 avgt 15 ≈ 10⁻³ MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space.norm > 128 avgt 15 ≈ 10⁻³ B/op > StringBuilders.toStringWithMixedChars:·gc.count > 128 avgt 15 116.000 counts > StringBuilders.toStringWithMixedChars:·gc.time > 128 avgt 15 86.000 ms > StringBuilders.toStringWithMixedChars > 256 avgt 15 1185.884 ± 137.364 ns/op > StringBuilders.toStringWithMixedChars:·gc.alloc.rate > 256 avgt 15 746.179 ± 92.534 MB/sec > StringBuilders.toStringWithMixedChars:·gc.alloc.rate.norm > 256 avgt 15 1376.244 ± 0.125 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space > 256 avgt 15 579.137 ± 208.636 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space.norm > 256 avgt 15 1055.150 ± 307.010 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space > 256 avgt 15 0.002 ± 0.002 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space.norm > 256 avgt 15 0.003 ± 0.003 B/op > StringBuilders.toStringWithMixedChars:·gc.count > 256 avgt 15 126.000 counts > StringBuilders.toStringWithMixedChars:·gc.time > 256 avgt 15 97.000 ms > StringBuilders.toStringWithMixedChars > 1024 avgt 15 4220.415 ± 440.169 ns/op > StringBuilders.toStringWithMixedChars:·gc.alloc.rate > 1024 avgt 15 791.945 ± 75.231 MB/sec > StringBuilders.toStringWithMixedChars:·gc.alloc.rate.norm > 1024 avgt 15 5217.435 ± 0.543 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space > 1024 avgt 15 657.270 ± 235.803 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Eden_Space.norm > 1024 avgt 15 4232.470 ± 1267.388 B/op > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space > 1024 avgt 15 0.005 ± 0.002 MB/sec > StringBuilders.toStringWithMixedChars:·gc.churn.G1_Survivor_Space.norm > 1024 avgt 15 0.033 ± 0.014 B/op > StringBuilders.toStringWithMixedChars:·gc.count > 1024 avgt 15 202.000 counts > StringBuilders.toStringWithMixedChars:·gc.time > 1024 avgt 15 121.000 ms
Xin Liu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision: - Merge branch 'master' into JDK-8282429 - split StringBuilder.toString() performance test out of StringBuilders.java - Change growOnly to maybeLatin. This patch also copys over the attribute from the other AbstractStringBuilder. Add a unit test to cover methods which cause maybeLatin1 becomes true. - make sure String(StringBuffer) is still synchronized. - Add a microbenchmark. - 8282429: StringBuilder/StringBuffer.toString() skip compressing for UTF16 strings ------------- Changes: - all: https://git.openjdk.java.net/jdk/pull/7671/files - new: https://git.openjdk.java.net/jdk/pull/7671/files/415929af..d8acc1f0 Webrevs: - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7671&range=03 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7671&range=02-03 Stats: 25201 lines in 1530 files changed: 15001 ins; 5266 del; 4934 mod Patch: https://git.openjdk.java.net/jdk/pull/7671.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/7671/head:pull/7671 PR: https://git.openjdk.java.net/jdk/pull/7671
