RFR: 8285519: Change usages of TimeUnit.convert to TimeUnit.toXXX

[Alan Bateman]

On Sat, 23 Apr 2022 21:02:50 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> TimeUnit.toMillis/toNanos/toMicros/toSeconds is shorter and a bit faster.
> Compared via JMH benchmark: 150ns -> 125ns/op
> <details>
> <summary>Benchamark adapted from http://cr.openjdk.java.net/~shade/8152083/TimeUnitBench.java</summary>
> 
> 
> @Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
> @Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
> @Fork(1)
> @State(Scope.Thread)
> @BenchmarkMode(Mode.AverageTime)
> @OutputTimeUnit(TimeUnit.NANOSECONDS)
> public class TimeUnitBench {
> 
>     static final int SIZE = TimeUnit.values().length * 10;
> 
>     @Param({"0", "1", "2", "3", "4", "5", "6", "-1"})
>     int bias;
> 
>     TimeUnit[] mod;
> 
>     @Setup
>     public void setup() {
>         mod = new TimeUnit[SIZE];
> 
>         TimeUnit[] vals = TimeUnit.values();
>         for (int c = 0; c < SIZE; c++) {
>             if (bias == -1) {
>                 // megamorphic
>                 mod[c] = vals[c % vals.length];
>             } else {
>                 mod[c] = vals[bias];
>             }
>         }
> 
>         Random r = new Random();
>         for (int c = 0; c < 10000; c++) {
>             int i = r.nextInt();
>             for (int o = 0; o < vals.length; o++) {
>                 if (vals[o].toNanos(i) != TimeUnit.NANOSECONDS.convert(i, vals[o]))
>                     throw new IllegalStateException("switch " + o);
>             }
>         }
>     }
> 
>     @Benchmark
>     public void const_convert(Blackhole bh) {
>         for (TimeUnit tu : mod) {
>             bh.consume(do_convert(tu));
>         }
>     }
> 
>     @Benchmark
>     public void value_convert(Blackhole bh) {
>         for (TimeUnit tu : mod) {
>             bh.consume(do_convert(tu, 1L));
>         }
>     }
> 
>     @Benchmark
>     public void const_toNanos(Blackhole bh) {
>         for (TimeUnit tu : mod) {
>             bh.consume(do_toNanos(tu));
>         }
>     }
> 
>     @Benchmark
>     public void value_toNanos(Blackhole bh) {
>         for (TimeUnit tu : mod) {
>             bh.consume(do_toNanos(tu, 1L));
>         }
>     }
> 
>     @CompilerControl(CompilerControl.Mode.DONT_INLINE)
>     private long do_toNanos(TimeUnit tu) {
>         return tu.toNanos(1L);
>     }
> 
>     @CompilerControl(CompilerControl.Mode.DONT_INLINE)
>     private long do_toNanos(TimeUnit tu, long value) {
>         return tu.toNanos(value);
>     }
> 
>     @CompilerControl(CompilerControl.Mode.DONT_INLINE)
>     private long do_convert(TimeUnit tu) {
>         return TimeUnit.NANOSECONDS.convert(1L, tu);
>     }
> 
>     @CompilerControl(CompilerControl.Mode.DONT_INLINE)
>     private long do_convert(TimeUnit tu, long value) {
>         return TimeUnit.NANOSECONDS.convert(value, tu);
>     }
> }
> 
> Results:
> 
> Benchmark                    (bias)  Mode  Cnt    Score    Error  Units
> TimeUnitBench.const_convert       0  avgt    5  151,856 ± 28,595  ns/op
> TimeUnitBench.const_convert       1  avgt    5  150,720 ± 23,863  ns/op
> TimeUnitBench.const_convert       2  avgt    5  151,432 ± 23,184  ns/op
> TimeUnitBench.const_convert       3  avgt    5  150,959 ± 24,726  ns/op
> TimeUnitBench.const_convert       4  avgt    5  150,966 ± 25,280  ns/op
> TimeUnitBench.const_convert       5  avgt    5  150,976 ± 25,542  ns/op
> TimeUnitBench.const_convert       6  avgt    5  151,118 ± 25,254  ns/op
> TimeUnitBench.const_convert      -1  avgt    5  152,673 ± 29,861  ns/op
> TimeUnitBench.const_toNanos       0  avgt    5  121,296 ± 25,236  ns/op
> TimeUnitBench.const_toNanos       1  avgt    5  121,707 ± 25,364  ns/op
> TimeUnitBench.const_toNanos       2  avgt    5  121,736 ± 25,726  ns/op
> TimeUnitBench.const_toNanos       3  avgt    5  121,822 ± 25,491  ns/op
> TimeUnitBench.const_toNanos       4  avgt    5  121,867 ± 26,090  ns/op
> TimeUnitBench.const_toNanos       5  avgt    5  121,927 ± 25,611  ns/op
> TimeUnitBench.const_toNanos       6  avgt    5  121,821 ± 25,843  ns/op
> TimeUnitBench.const_toNanos      -1  avgt    5  121,923 ± 25,206  ns/op
> TimeUnitBench.value_convert       0  avgt    5  150,525 ± 25,439  ns/op
> TimeUnitBench.value_convert       1  avgt    5  151,098 ± 24,024  ns/op
> TimeUnitBench.value_convert       2  avgt    5  151,259 ± 25,381  ns/op
> TimeUnitBench.value_convert       3  avgt    5  151,030 ± 25,548  ns/op
> TimeUnitBench.value_convert       4  avgt    5  151,290 ± 25,998  ns/op
> TimeUnitBench.value_convert       5  avgt    5  151,006 ± 25,448  ns/op
> TimeUnitBench.value_convert       6  avgt    5  150,945 ± 25,314  ns/op
> TimeUnitBench.value_convert      -1  avgt    5  151,186 ± 25,814  ns/op
> TimeUnitBench.value_toNanos       0  avgt    5  121,556 ± 25,745  ns/op
> TimeUnitBench.value_toNanos       1  avgt    5  123,410 ± 22,323  ns/op
> TimeUnitBench.value_toNanos       2  avgt    5  125,452 ± 26,575  ns/op
> TimeUnitBench.value_toNanos       3  avgt    5  125,297 ± 26,204  ns/op
> TimeUnitBench.value_toNanos       4  avgt    5  125,357 ± 26,085  ns/op
> TimeUnitBench.value_toNanos       5  avgt    5  125,165 ± 26,185  ns/op
> TimeUnitBench.value_toNanos       6  avgt    5  125,536 ± 25,487  ns/op
> TimeUnitBench.value_toNanos      -1  avgt    5  125,460 ± 25,063  ns/op
> 
> 
> </details>

The changes to the Selector implementations to use toXXX look okay. Note that it's not performance critical as it is only executed when a thread blocked in epoll_wait/equivalent is interrupted by a signal, it's not a normal code path.

-------------

PR: https://git.openjdk.java.net/jdk/pull/8376