On Sun, 17 Sep 2023 16:01:33 GMT, Shaojin Wen <d...@openjdk.org> wrote:
> @cl4es made performance optimizations for the simple specifiers of > String.format in PR https://github.com/openjdk/jdk/pull/2830. Based on the > same idea, I continued to make improvements. I made patterns like %2d %02d > also be optimized. > > The following are the test results based on MacBookPro M1 Pro: > > > -Benchmark Mode Cnt Score Error Units > -StringFormat.complexFormat avgt 15 1862.233 ? 217.479 ns/op > -StringFormat.int02Format avgt 15 312.491 ? 26.021 ns/op > -StringFormat.intFormat avgt 15 84.432 ? 4.145 ns/op > -StringFormat.longFormat avgt 15 87.330 ? 6.111 ns/op > -StringFormat.stringFormat avgt 15 63.985 ? 11.366 ns/op > -StringFormat.stringIntFormat avgt 15 87.422 ? 0.147 ns/op > -StringFormat.widthStringFormat avgt 15 250.740 ? 32.639 ns/op > -StringFormat.widthStringIntFormat avgt 15 312.474 ? 16.309 ns/op > > +Benchmark Mode Cnt Score Error Units > +StringFormat.complexFormat avgt 15 740.626 ? 66.671 ns/op > (+151.45) > +StringFormat.int02Format avgt 15 131.049 ? 0.432 ns/op > (+138.46) > +StringFormat.intFormat avgt 15 67.229 ? 4.155 ns/op > (+25.59) > +StringFormat.longFormat avgt 15 66.444 ? 0.614 ns/op > (+31.44) > +StringFormat.stringFormat avgt 15 62.619 ? 4.652 ns/op (+2.19) > +StringFormat.stringIntFormat avgt 15 89.606 ? 13.966 ns/op (-2.44) > +StringFormat.widthStringFormat avgt 15 52.462 ? 15.649 ns/op > (+377.95) > +StringFormat.widthStringIntFormat avgt 15 101.814 ? 3.147 ns/op > (+206.91) It might be reasonable to add a few more common patterns to the `FormatSpecifier` fast-path, but where to draw the line? FWIW the intent of micros like `complex` and `widthString` wasn't necessarily to invite further optimizations, but to explore the cost of failure, i.e., make sure that the fast-path doesn't add a substantial cost when it doesn't help or only helps somewhat. Since you now specialize for most of the patterns in the micros I think you need to explore some variants that you _don't_ optimize for, such as `"%10.3f"`. Orthogonal optimizations like the `FormatSpecifier` fast-path extension and the `print` fast-path should generally be separate PRs. I think it would make sense to make the testing a bit more exhaustive, especially w.r.t argument indexes and specifiers taking multiple flags. Looking at test/jdk/java/util/Formatter/Basic-X.java.template we seem to test each flag, but lack tests combining many flags and permutations thereof. Could you take a stab at increasing coverage a bit here? I'm also curious what performance numbers you get with the latest patch. If we go all the way like this some of the added microbenchmarks is a bit pointless so after checking you might want to cut back on some of those (just keep one of the floating point tests maybe) I think this is shaping up nicely. Some unused code, then I think we can move ahead. The new `FormatSpecifierParser` utility class adds a bit of boilerplate for something that could be a static utility: https://github.com/wenshao/jdk/pull/6 - but perhaps splitting it up a bit more helps JIT inlining further. I can take this on as a follow-up RFE if you prefer. A few nits, otherwise I think this looks OK I was worried this would sprawl out more, but perhaps ~230 lines of code is a reasonable extra weight to make the long tail of `String.format`'s regex-free. I was going to comment that the flag parsing was broken in f303f29 but it seems that it was fixed in the latest. I think we need to make a review pass over all existing tests to make sure all imaginable variants are covered. The parser code also ought to be shared between `Formatter` and `FormatProcessor` so that there's a single source of truth going forward. I think it makes sense to file an RFE and do a full review of this. "Regex-free parsing of Formatter and FormatProcessor specifiers"? Please don't pile on new refactorings and improvements on a PR that has been opened for review. Better to let things brew as a draft for a bit if you're not sure you're done before opening the PR for review, then once it's been opened (like this one) consider preparing follow-up PR instead of refactoring as you go. Specifically I'm not sure 0d977b2 is a good idea and would like you to roll those changes back. Object pooling for trivial, short-lived objects are considered an anti-pattern, as they add references to old GC generations and share many of the same drawbacks as lookup tables, such as increased cache traffic. Showing great wins on microbenchmarks while being a wash or even regressing real applications. src/java.base/share/classes/java/util/Formatter.java line 2944: > 2942: ++off; > 2943: argSize = size + 1; > 2944: size = 0; pointless `size = 0` src/java.base/share/classes/java/util/Formatter.java line 2949: > 2947: } > 2948: } else { > 2949: if (first == '0') { While it's clever to avoid re-parsing I think it muddies the control flow. It would be simpler if we always reset to `off = start; c = first` in this `else` block then unconditionally call `parseFlags(); parseWidth();` outside in `parse`. The few extra calls to `s.charAt(..)` this might add a little overhead on some tests, but the JIT might like the brevity and less branchy structure overall and on larger benchmarks.. Maybe worth experimenting with. src/java.base/share/classes/java/util/Formatter.java line 2964: > 2962: widthSize = size; > 2963: } > 2964: size = 0; Pointless `size = 0` src/java.base/share/classes/java/util/Formatter.java line 2977: > 2975: if (!Flags.isFlag(c)) { > 2976: flagSize = size; > 2977: size = 0; pointless `size = 0` src/java.base/share/classes/java/util/Formatter.java line 3011: > 3009: > 3010: static boolean isConversion(char c) { > 3011: return (c >= 'a' && c <= 'z') || (c >= 'A' || c <= 'Z') || c == > '%'; Logical error: Suggestion: return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '%'; src/java.base/share/classes/java/util/Formatter.java line 3140: > 3138: } > 3139: > 3140: FormatSpecifier(char conv, int flag, int width, int precision) { This appears to be unused. src/java.base/share/classes/java/util/Formatter.java line 3420: > 3418: && fmt.a instanceof StringBuilder sb > 3419: ) { > 3420: sb.append(value); There's a lot of `if`s here, and this doesn't take into account locales with non-ASCII digits: Locale ar = new Locale.Builder().setLanguageTag("ar-SA-u-nu-arab").build(); Locale.setDefault(ar); System.out.println("%d".formatted(10000)); // should print "١٠٠٠٠" but prints "10000" test/jdk/java/util/Formatter/Basic-X.java.template line 1748: > 1746: // perhaps an IllegalFormatArgumentIndexException should be > defined? > 1747: tryCatch("%<%", IllegalFormatFlagsException.class); > 1748: After adding test-cases to this template you need to run `genBasic.sh` (in the same folder) to regenerate all the `Basic*` tests. These changes then need to be added to the PR. FWIW these new and existing tests that provoke `IllegalFormatPrecisionException` and `UnknownFormatConversionException` are common to all types, meaning there seems to be little point in generating them out into each and every `BasicByte`, `BasicInt` et.c.. Perhaps it would make more sense to add such tests directly to Basic.java to avoid some redundancy here - or a new `BasicCommon` test to put common tests into? ------------- PR Review: https://git.openjdk.org/jdk/pull/15776#pullrequestreview-1630133740 PR Review: https://git.openjdk.org/jdk/pull/15776#pullrequestreview-1639452604 Changes requested by redestad (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/15776#pullrequestreview-1641781843 Marked as reviewed by redestad (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/15776#pullrequestreview-1641961236 PR Comment: https://git.openjdk.org/jdk/pull/15776#issuecomment-1728424181 PR Comment: https://git.openjdk.org/jdk/pull/15776#issuecomment-1730173405 PR Comment: https://git.openjdk.org/jdk/pull/15776#issuecomment-1732562759 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1335806486 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1335817101 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1335817800 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1335779111 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1335234147 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1335667901 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1328152682 PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1350933399
