[jdk16] RFR: 8260473: [vector] ZGC: VectorReshape test produces incorrect results with ZGC enabled

[Vladimir Ivanov]

On Mon, 1 Feb 2021 12:15:38 GMT, 王超 <github.com+25214855+casparcwang at openjdk.org> wrote:

>>> > compileonly and compilercount=1 will let the VM run slow enough to wait for a gc to be finished.
>>> 
>>> That's a strange way to provoke the bug. You could just increase the number of iterations instead.
>>> 
>>> But the right way to fix it is to stress ZGC to continuously run in the background while the test case aggressively unboxes vectors in compiled code. `-Xmx256m` helps with that while `-XX:CICompilerCount=1` is irrelevant.
>> 
>> Yes, it's very weird to provoke the bug like this. If CICompilerCount=1 is removed, the test failed 60% roughly on my machine.
>> And the iteration has already changed from 100 to 1000,  the run time of the test is nearly 30s on release version of jvm.
>> 
>> If I add the following patch, the test always fails on my machine,
>> 
>> diff --git a/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java b/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
>> index 1843ec0..959b29a 100644
>> --- a/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
>> +++ b/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
>> @@ -44,7 +44,7 @@ import jdk.internal.vm.annotation.ForceInline;
>>   * @modules jdk.incubator.vector
>>   * @modules java.base/jdk.internal.vm.annotation
>>   * @run testng/othervm -XX:CompileCommand=compileonly,jdk/incubator/vector/ByteVector.fromByteBuffer
>> - *      -XX:-TieredCompilation -XX:CICompilerCount=1 -XX:+UseZGC -Xbatch -Xmx256m VectorRebracket128Test
>> + *      -XX:-TieredCompilation -XX:+UseZGC -Xmx256m VectorRebracket128Test
>>   */
>>  
>>  @Test
>> @@ -125,6 +125,14 @@ public class VectorRebracket128Test {
>>      @ForceInline
>>      static <E,F>
>>      void testVectorRebracket(VectorSpecies<E> a, VectorSpecies<F> b, byte[] input, byte[] output) {
>> +        new Thread(() -> {
>> +            while (true) {
>> +                try {
>> +                    System.gc();
>> +                    Thread.sleep(100);
>> +                } catch (Exception e) {}
>> +            }
>> +        }).start();
>>          Vector<E> av = a.fromByteArray(input, 0, ByteOrder.nativeOrder());
>>          int block;
>>          assert(input.length == output.length);
>
> sorry for the wrong patch above,  the failed reason of the patch above is due to stack creation failure (create 1000 threads). The following is the right stress gc patch.
> 
> diff --git a/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java b/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
> index 6b266db..a761ea2 100644
> --- a/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
> +++ b/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
> @@ -44,7 +44,7 @@ import jdk.internal.vm.annotation.ForceInline;
>   * @modules jdk.incubator.vector
>   * @modules java.base/jdk.internal.vm.annotation
>   * @run testng/othervm -XX:CompileCommand=compileonly,jdk/incubator/vector/ByteVector.fromByteBuffer
> - *      -XX:-TieredCompilation -XX:CICompilerCount=1 -XX:+UseZGC -Xbatch -Xmx256m VectorRebracket128Test
> + *      -XX:-TieredCompilation -XX:+UseZGC -Xmx256m VectorRebracket128Test
>   */
>  
>  @Test
> @@ -59,6 +59,19 @@ public class VectorRebracket128Test {
>      static final VectorSpecies<Byte> bspec128 = ByteVector.SPECIES_128;
>      static final VectorSpecies<Short> sspec128 = ShortVector.SPECIES_128;
>  
> +    static {
> +        Thread t = new Thread(() -> {
> +            while (true) {
> +                try {
> +                    System.gc();
> +                    Thread.sleep(100);
> +                } catch (Exception e) {}
> +            }
> +        });
> +        t.setDaemon(true);
> +        t.start();
> +    }
> +
>      static <T> IntFunction<T> withToString(String s, IntFunction<T> f) {
>          return new IntFunction<T>() {
>              @Override

Good. Please, file a follow-up RFE to improve the test.

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

PR: https://git.openjdk.java.net/jdk16/pull/139