On Mon, 30 Mar 2026 11:49:46 GMT, Roman Kennke <[email protected]> wrote:
>> I analyzed the performance of Thread.setName() in response to a customer >> workload running Cassandra, where Thread.setName() showed up (mostly because >> of rather pathetic use of setName() from Cassanda *sigh*). >> >> Profiling showed that most time (around 75%) is spent in the actual syscall, >> so there are limits on what we can do. There is some fixed overheads like >> the cost for synchronized, and also some costs that scale with the length of >> the name, most importantly the UTF8 conversion. >> >> I implemented the following improvements: >> - Removed synchronized from setName(), as suggested by some folks in the >> JBS issue. This saves ~15 nanoseconds. Not sure if the method could be >> called contended by Cassandra, if so, the savings might be much larger. >> - Almost all thread names are Latin1/ASCII, and there is no need to convert >> to UTF8 in that case. Also, the various OS APIs to set the thread name don't >> even seem to specify the character encoding. Avoiding the UTF8 conversion >> brings down the length-dependent costs. In many cases we can also pass down >> the backing array of the string and avoid copying. >> - When the name doesn't change, we can skip updating the native name, which >> makes setName() almost a no-op. >> - For truncating the name on Linux to 16 chars, instead of using snprintf >> with a pattern, we can simply stitch together the name directly (first 7 >> chars, last 6 chars, 2 dots in between), this saves ~100ns. >> >> In the end, we bring down performance for the small cases by ~7%, longer >> names by ~20% and completely removed the conversion overhead that primarily >> affected longer names. >> >> | Benchmark | (length) | Baseline (ns/op) | Optimized (ns/op) | Change >> | >> >> |---------------|----------|------------------:|-------------------:|--------:| >> | setName | 1 | 602.3 ± 2.0 | 561.9 ± 1.5 | >> -6.7% | >> | setName | 4 | 605.9 ± 2.1 | 570.2 ± 1.2 | >> -5.9% | >> | setName | 15 | 617.1 ± 2.7 | 570.4 ± 2.8 | >> -7.6% | >> | setName | 16 | 712.1 ± 6.0 | 569.4 ± 2.7 | >> -20.0% | >> | setName | 50 | 757.9 ± 5.2 | 566.3 ± 4.6 | >> -25.3% | >> | setName | 200 | 986.2 ± 2.7 | 569.9 ± 4.9 | >> -42.2% | >> | setNameSame | 1 | — | 7.4 ± 0.0 | — >> | >> | setNameSame | 4 | — | 7.4 ± 0.0 | — >> | >> | setNameSame | 15 | —... > > Roman Kennke has updated the pull request incrementally with one additional > commit since the last revision: > > Revert synchronized and remove unused code Please update the PR (and JBS?) description to reflect the proposed changes that are no longer being made. Also there are a number of suggestions in the existing PR comments that have yet to be responded to. ------------- PR Comment: https://git.openjdk.org/jdk/pull/30374#issuecomment-4159893658
