Vectorization of Unsafe.putByte()

[Paul Sandoz]

Hi,

I chatted with Vladimir a bit about this. Since we trust code within DirectByteBuffer to do the right thing, it should be possible vectorize since the boundaries and type are known, we *just* need to teach the JIT about ‘em.

There is also another solution being cooked up. An explicit API for vectorization being actively worked on under project Panama, where vectors can be loaded from DBBs.

Paul.

> On Feb 23, 2018, at 5:08 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
> Hi Vlad,
> 
> Vectorization in HotSpot JVM does not work with direct addresses. It only works with Java arrays where boundaries and element type is known. For Java arrays Unsafe access converted to normal access to array's elements and vectorization is working.
> 
> Regards,
> Vladimir K
> 
> On 2/22/18 2:13 PM, vrozov wrote:
>> Hi,
>> What is a reason that Unsafe.putByte(Object var1, long var2, byte var4) is
>> vectorized differently compared to Unsafe.putByte(long var1, byte var3)?
>> Below are results of JMH with Java 8 on my Mac. Results for Java 9 and 10
>> are similar.
>> DirectBufferBenchmark.testNettyDirectPutBytes  avgt       87.490
>> ms/op
>> DirectBufferBenchmark.testNettyHeapPutBytes    avgt       23.782
>> ms/op
>> @State(Scope.Thread)
>> @BenchmarkMode(Mode.AverageTime)
>> @OutputTimeUnit(TimeUnit.MILLISECONDS)
>> public class DirectBufferBenchmark {
>>   private static final int capacity = 256 * 1024 * 1024;
>>   private final ByteBuffer direct_source =
>> ByteBuffer.allocateDirect(capacity);
>>   private final ByteBuffer direct_target =
>> ByteBuffer.allocateDirect(capacity);
>>   private final ByteBuffer heap_source = ByteBuffer.allocate(capacity);
>>   private final ByteBuffer heap_target = ByteBuffer.allocate(capacity);
>>   private final long direct_source_address =
>> PlatformDependent.directBufferAddress(direct_source);
>>   private final long direct_target_address =
>> PlatformDependent.directBufferAddress(direct_target);
>>   private final byte[] heap_source_array = heap_source.array();
>>   private final byte[] heap_target_array = heap_target.array();
>>   @Benchmark
>>   public void testNettyHeapPutBytes() {
>>     for (int i = 0; i < capacity; i++) {
>>       PlatformDependent.putByte(heap_target_array, i, (byte)0xFF);
>>     }
>>   }
>>   @Benchmark
>>   public void testNettyDirectPutBytes() {
>>     for (int i = 0; i < capacity; i++) {
>>       PlatformDependent.putByte(direct_target_address + i, (byte)0xFF);
>>     }
>>   }
>> }
>> Thank you,
>> Vlad
>> --
>> Sent from: http://openjdk.5641.n7.nabble.com/OpenJDK-Hotspot-Compiler-Development-List-f6935.html