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

[王超]

On Mon, 1 Feb 2021 12:06:26 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.
>
>> > 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

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