ODP: Foreign + Vectors - benchmarks for copying and swapping

[Radosław Smogura]

Hi,

I think why the copy case may fail with unrolling, because

  *   loop unroll takes the range check from intoByteBuffer as the loop exit condition
  *   the range check uses unsigned compare, which is not supported by loop unroll

I think in this code
        for (int i = 0; i < bound; i += lanes) {
          final var srcVector = ByteVector
              .fromByteBuffer(BYTE_VECTOR_SPECIES, src, i, ByteOrder.nativeOrder());

          srcVector.intoByteBuffer(dst, i, ByteOrder.nativeOrder());
        }
exit condition should be i < bound, not a range check from intoByteBuffer.

Kind regards,
Rado

________________________________
Od: Paul Sandoz <paul.sandoz at oracle.com>
Wysłane: poniedziałek, 21 czerwca 2021 23:25
Do: Maurizio Cimadamore <maurizio.cimadamore at oracle.com>
DW: Radosław Smogura <mail at smogura.eu>; Vladimir Ivanov <vladimir.x.ivanov at oracle.com>; panama-dev at openjdk.java.net <panama-dev at openjdk.java.net>
Temat: Re: Foreign + Vectors - benchmarks for copying and swapping

Replacing the upper bound in `segmentImplicitScalar` with a constant (1024 say) results in a similar time to `bufferNativeScalar` without a constant bound, both of which (alas) are still slower that scalar array access (which benefits greatly from auto-vectorization).

I wonder if the segment subrange checking for int value ranges is having an impact on bounds checking?

Paul.

> On Jun 21, 2021, at 1:56 PM, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
>
>
> On 21/06/2021 20:33, Paul Sandoz wrote:
>> - Segment scalar access is penalized compared to ByteBuffer (from allocate or allocateDirect) scalar access.
>
> Odd
>
> We have many benchmarks similar to this (see LoopOverNonConstant) and they seem to offer same level of performance compared with ByteBuffers.
>
> I wonder if the loop limit being "SPECIES.loopBound(srcArray.length)" plays a role? Have you tried replacing that expression with a constant?
>
> Maurizio
>