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From Adam Roberts <AROBE...@uk.ibm.com>
Subject Re: BytesToBytes and unaligned memory
Date Fri, 15 Apr 2016 15:32:47 GMT
Ted, yep I'm working from the latest code which includes that unaligned 
check, for experimenting I've modified that code to ignore the unaligned 
check (just go ahead and say we support it anyway, even though our JDK 
returns false: the return value of java.nio.Bits.unaligned()).

My Platform.java for testing contains:

private static final boolean unaligned;

static {
  boolean _unaligned;
  // use reflection to access unaligned field
  try {
    System.out.println("Checking unaligned support");
    Class<?> bitsClass =
      Class.forName("java.nio.Bits", false, 
ClassLoader.getSystemClassLoader());
    Method unalignedMethod = bitsClass.getDeclaredMethod("unaligned");
    unalignedMethod.setAccessible(true);
    _unaligned = Boolean.TRUE.equals(unalignedMethod.invoke(null));
    System.out.println("Used reflection and _unaligned is: " + 
_unaligned);
    System.out.println("Setting to true anyway for experimenting");
    _unaligned = true;
    } catch (Throwable t) {
      // We at least know x86 and x64 support unaligned access.
      String arch = System.getProperty("os.arch", "");
      //noinspection DynamicRegexReplaceableByCompiledPattern
      // We don't actually get here since we find the unaligned method OK 
and it returns false (I override with true anyway)
      // but add s390x incase we somehow fail anyway.
      System.out.println("Checking for s390x, os.arch is: " + arch);
      _unaligned = arch.matches("^(i[3-6]86|x86(_64)?|x64|s390x|amd64)$");
    }
    unaligned = _unaligned;
    System.out.println("returning: " + unaligned);
  }
}

Output is, as you'd expect, "used reflection and _unaligned is false, 
setting to true anyway for experimenting", and the tests pass.

No other problems on the platform (pending a different pull request).

Cheers,







From:   Ted Yu <yuzhihong@gmail.com>
To:     Adam Roberts/UK/IBM@IBMGB
Cc:     "dev@spark.apache.org" <dev@spark.apache.org>
Date:   15/04/2016 15:32
Subject:        Re: BytesToBytes and unaligned memory



I assume you tested 2.0 with SPARK-12181 .

Related code from Platform.java if java.nio.Bits#unaligned() throws 
exception:

      // We at least know x86 and x64 support unaligned access.
      String arch = System.getProperty("os.arch", "");
      //noinspection DynamicRegexReplaceableByCompiledPattern
      _unaligned = arch.matches("^(i[3-6]86|x86(_64)?|x64|amd64)$");

Can you give us some detail on how the code runs for JDKs on zSystems ?

Thanks

On Fri, Apr 15, 2016 at 7:01 AM, Adam Roberts <AROBERTS@uk.ibm.com> wrote:
Hi, I'm testing Spark 2.0.0 on various architectures and have a question, 
are we sure if 
core/src/test/java/org/apache/spark/unsafe/map/AbstractBytesToBytesMapSuite.java 
really is attempting to use unaligned memory access (for the 
BytesToBytesMapOffHeapSuite tests specifically)? 

Our JDKs on zSystems for example return false for the 
java.nio.Bits.unaligned() method and yet if I skip this check and add 
s390x to the supported architectures (for zSystems), all thirteen tests 
here pass. 

The 13 tests here all fail as we do not pass the unaligned requirement 
(but perhaps incorrectly): 
core/src/test/java/org/apache/spark/unsafe/map/BytesToBytesMapOffHeapSuite.java 
and I know the unaligned checking is at 
common/unsafe/src/main/java/org/apache/spark/unsafe/Platform.java 

Either our JDK's method is returning false incorrectly or this test isn't 
using unaligned memory access (so the requirement is invalid), there's no 
mention of alignment in the test itself. 

Any guidance would be very much appreciated, cheers 


Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU


Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

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