RFR: 8340232: Optimize DataInputStream::readUTF

[Shaojin Wen]

On Sun, 8 Sep 2024 07:52:26 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> Similar to ObjectInputStream, use JLA.countPositives and JLA.inflateBytesToChars to speed up readUTF

In the readUTFAscii scenario, the performance is significantly improved, but in the readUTFSmall scenario, the performance is regressed.

Here are the performance numbers on the MacBook M1 Pro:

## Script


# baseline
git checkout fbe2629303bcee5855673b7e37d8c49f19dc9849
make test TEST="micro:java.io.DataInputStreamTest.readUTF"

# current
git checkout 5c4bd6db977ca8729e078d26cb7ca284ab42203c
make test TEST="micro:java.io.DataInputStreamTest.readUTF"



## Performance Numbers


-# baseline
-Benchmark                              Mode  Cnt  Score   Error  Units
-DataInputStreamTest.readUTFAsciiLarge  avgt   20  1.401 ? 0.005  us/op
-DataInputStreamTest.readUTFAsciiMixed  avgt   20  1.337 ? 0.092  us/op
-DataInputStreamTest.readUTFAsciiSmall  avgt   20  0.872 ? 0.004  us/op
-DataInputStreamTest.readUTFLarge       avgt   20  2.178 ? 0.050  us/op
-DataInputStreamTest.readUTFMixed       avgt   20  1.700 ? 0.109  us/op
-DataInputStreamTest.readUTFSmall       avgt   20  0.879 ? 0.012  us/op

+# current
+Benchmark                              Mode  Cnt  Score   Error  Units
+DataInputStreamTest.readUTFAsciiLarge  avgt   20  0.833 ? 0.004  us/op
+DataInputStreamTest.readUTFAsciiMixed  avgt   20  0.804 ? 0.001  us/op
+DataInputStreamTest.readUTFAsciiSmall  avgt   20  0.828 ? 0.005  us/op
+DataInputStreamTest.readUTFLarge       avgt   20  2.053 ? 0.063  us/op
+DataInputStreamTest.readUTFMixed       avgt   20  1.675 ? 0.056  us/op
+DataInputStreamTest.readUTFSmall       avgt   20  1.834 ? 0.026  us/op


|   | baseline  | current | delta |
| --- | --- | --- | --- |
| DataInputStreamTest.readUTFAsciiLarge | 1.401 | 0.833 | 68.19% |
| DataInputStreamTest.readUTFAsciiMixed | 1.337 | 0.804 | 66.29% |
| DataInputStreamTest.readUTFAsciiSmall | 0.872 | 0.828 | 5.31% |
| DataInputStreamTest.readUTFLarge | 2.178 | 2.053 | 6.09% |
| DataInputStreamTest.readUTFMixed | 1.700 | 1.675 | 1.49% |
| DataInputStreamTest.readUTFSmall | 0.879 | 1.834 | -52.07% |

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PR Comment: https://git.openjdk.org/jdk/pull/20903#issuecomment-2347702045