Foreign + Vectors - benchmarks for copying and swapping

[Paul Sandoz]

In general that should be ok. Try using IntVector instead and it will unroll (with your patch removing CPU barriers)

I wonder if this may be a limitation specific to bytes. 

Paul.

> On Jun 21, 2021, at 4:28 PM, Radosław Smogura <mail at smogura.eu> wrote:
> 
> 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
> >