Using the Vector API on (externally allocated) foreign memory

[Paul Sandoz]

Hi,

Do you have a JMH benchmark to share?  That’s helpful so we know we are talking more precisely about the same thing, further it means we can look at the hotspots of the generated machine code and identify C2 issues.

IIRC currently the performance focus has been mostly on fromArray/toArray using corresponding primitive array so I could imagine there are some perf issues to be resolved.  However both primitive array access and buffer access use the same load intrinsic.

Some things to explore (if you have not done so already):

- ensure the byte order is native order to avoid byte swapping.

- compare with fromByteArray

- switch off bounds checking using the system property “jdk.incubator.vector.VECTOR_ACCESS_OOB_CHECK”:

static final int VECTOR_ACCESS_OOB_CHECK = Integer.getInteger("jdk.incubator.vector.VECTOR_ACCESS_OOB_CHECK", 2);

…

@ForceInline
static int checkFromIndexSize(int ix, int vlen, int length) {
    switch (VectorIntrinsics.VECTOR_ACCESS_OOB_CHECK) {
        case 0: return ix; // no range check
        case 1: return Objects.checkFromIndexSize(ix, vlen, length);
        case 2: return Objects.checkIndex(ix, length - (vlen - 1));
        default: throw new InternalError();
    }
}

Hth,
Paul. 

> On Mar 9, 2020, at 4:02 AM, Antoine Chambille <ach at activeviam.com> wrote:
> 
> Hi John, thank you for the suggestion, wrapping native memory with a
> ByteBuffer does work (com.sun.jna.Pointer.getByteBuffer(long address)).
> 
> However after running a few benchmarks it looks like the code loading
> vectors from byte buffers is about twice slower than the same code loading
> vectors from java arrays. Is this expected?
> 
> JDK freshly checked out and built for Windows 10 (
> http://hg.openjdk.java.net/panama/dev -b vectorIntrinsics ). double[] data,
> AVX2, Intel.
> 
> 
> Best,
> -Antoine
> 
> 
> 
> On Fri, Mar 6, 2020 at 8:43 PM John Rose <john.r.rose at oracle.com> wrote:
> 
>> On Mar 6, 2020, at 9:59 AM, Antoine Chambille <ach at activeviam.com> wrote:
>> 
>> 
>> Is support for vector operations on (externally allocated) foreign memory
>> being considered? Have we missed something?
>> 
>> 
>> The current story is that you have to wrap a byte buffer around
>> your native memory, using JNI’s NewDirectByteBuffer.  Please
>> let us know if that doesn’t work for you.
>> 
>> It is likely that vectors will interoperate with a more modern API
>> for both on-heap and off-heap access, after it settles.  These “memory
>> segments” are incubating in JDK 14:
>> 
>> 
>> https://download.java.net/java/GA/jdk14/docs/api/jdk.incubator.foreign/jdk/incubator/foreign/MemorySegment.html
>> 
>> — John
>> 
> 
> 
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