+1
> On Dec 7, 2018, at 8:11 PM, Claes Redestad <claes.redes...@oracle.com> wrote: > > Hi, > > following up from discussions during review of JDK-8214971[1], I > examined the startup and peak performance of a few different variant of > writing String::equals. > > Webrev: http://cr.openjdk.java.net/~redestad/8215017/jdk.00/ > Bug: https://bugs.openjdk.java.net/browse/JDK-8215017 > > - folding coder() == aString.coder() into sameCoder(aString) helps > interpreter without adversely affecting higher optimization levels > > - Jim's proposal to use Arrays.equals is _interesting_: it improves > peak performance on some inputs but regress it on others. I'll defer > that to a future RFE as it needs a more thorough examination. > > - what we can do is simplify to only use StringLatin1.equals. If I'm not > completely mistaken these are all semantically neutral (and > StringUTF16.equals effectively redundant). If I'm completely wrong here > I'll welcome the learning opportunity. :-) > > This removes a branch and two method calls, and for UTF16 Strings we'll > use a simpler algorithm early, which turns out to be beneficial during > interpreter and C1 level. > > I added a simple microbenchmark to explore this, results show 1.2-2.5x > improvements in interpreter performance, while remaining perfectly > neutral results for optimized code on this simple micro[2]. > > This could be extended to clean up and move StringLatin1.equals back > into String and remove StringUTF16, but we'd also need to rearrange the > intrinsics on the VM side. Let me know what you think. > > Thanks! > > /Claes > > [1] > http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-December/057162.html > > [2] > ========== Baseline ================= > > -Xint > Benchmark Mode Cnt Score Error Units > StringEquals.equalsAlmostEqual avgt 4 968.640 ± 1.337 ns/op > StringEquals.equalsAlmostEqualUTF16 avgt 4 2082.007 ± 5.303 ns/op > StringEquals.equalsDifferent avgt 4 583.166 ± 29.461 ns/op > StringEquals.equalsDifferentCoders avgt 4 422.993 ± 1.291 ns/op > StringEquals.equalsEqual avgt 4 988.671 ± 1.492 ns/op > StringEquals.equalsEqualsUTF16 avgt 4 2103.060 ± 5.705 ns/op > > -XX:+CompactStrings > Benchmark Mode Cnt Score Error Units > StringEquals.equalsAlmostEqual avgt 4 23.896 ± 0.089 ns/op > StringEquals.equalsAlmostEqualUTF16 avgt 4 23.935 ± 0.562 ns/op > StringEquals.equalsDifferent avgt 4 15.086 ± 0.044 ns/op > StringEquals.equalsDifferentCoders avgt 4 12.572 ± 0.008 ns/op > StringEquals.equalsEqual avgt 4 25.143 ± 0.025 ns/op > StringEquals.equalsEqualsUTF16 avgt 4 25.148 ± 0.021 ns/op > > -XX:-CompactStrings > Benchmark Mode Cnt Score Error Units > StringEquals.equalsAlmostEqual avgt 4 24.539 ± 0.127 ns/op > StringEquals.equalsAlmostEqualUTF16 avgt 4 22.638 ± 0.047 ns/op > StringEquals.equalsDifferent avgt 4 13.930 ± 0.835 ns/op > StringEquals.equalsDifferentCoders avgt 4 13.836 ± 0.025 ns/op > StringEquals.equalsEqual avgt 4 26.420 ± 0.020 ns/op > StringEquals.equalsEqualsUTF16 avgt 4 23.889 ± 0.037 ns/op > > ========== Fix ====================== > > -Xint > Benchmark Mode Cnt Score Error Units > StringEquals.equalsAlmostEqual avgt 4 811.859 ± 8.663 ns/op > StringEquals.equalsAlmostEqualUTF16 avgt 4 802.784 ± 352.884 ns/op > StringEquals.equalsDifferent avgt 4 431.837 ± 1.884 ns/op > StringEquals.equalsDifferentCoders avgt 4 358.244 ± 1.208 ns/op > StringEquals.equalsEqual avgt 4 832.056 ± 3.541 ns/op > StringEquals.equalsEqualsUTF16 avgt 4 832.434 ± 3.516 ns/op > > -XX:+CompactStrings > Benchmark Mode Cnt Score Error Units > StringEquals.equalsAlmostEqual avgt 4 23.906 ± 0.151 ns/op > StringEquals.equalsAlmostEqualUTF16 avgt 4 23.905 ± 0.123 ns/op > StringEquals.equalsDifferent avgt 4 15.088 ± 0.023 ns/op > StringEquals.equalsDifferentCoders avgt 4 12.575 ± 0.030 ns/op > StringEquals.equalsEqual avgt 4 25.149 ± 0.059 ns/op > StringEquals.equalsEqualsUTF16 avgt 4 25.149 ± 0.033 ns/op > > -XX:-CompactStrings > Benchmark Mode Cnt Score Error Units > StringEquals.equalsAlmostEqual avgt 4 24.521 ± 0.050 ns/op > StringEquals.equalsAlmostEqualUTF16 avgt 4 22.639 ± 0.035 ns/op > StringEquals.equalsDifferent avgt 4 13.831 ± 0.020 ns/op > StringEquals.equalsDifferentCoders avgt 4 13.884 ± 0.345 ns/op > StringEquals.equalsEqual avgt 4 26.395 ± 0.066 ns/op > StringEquals.equalsEqualsUTF16 avgt 4 23.904 ± 0.112 ns/op
