RFR: 8256536: Newer AMD 19h (EPYC) Processor family defaults

[Rohit Arul Raj]

On Wed, 18 Nov 2020 10:36:03 GMT, Rohit Arul Raj <rraj at openjdk.org> wrote:

> This patch sets the following flags as defaults for newer AMD 19h (EPYC) processors.
>       bool UseFPUForSpilling               = true   
>       bool UseUnalignedLoadStores    = true   
>       bool UseXMMForArrayCopy        = true   
>       bool UseXMMForObjInit             = true   
>       bool UseFastStosb                       = false  
>       bool AlignVector                          = false  
> 
> Additional testing: make run-test TEST="tier1 tier2" JTREG="JOBS=128" CONF=linux-x86_64-server-fastdebug
> 
> Please review this change.
> 
> Thanks,
> Rohit

> On 18/11/2020 8:41 pm, Rohit Arul Raj wrote:
> 
> > This patch sets the following flags as defaults for newer AMD 19h (EPYC) processors.
> > bool UseFPUForSpilling               = true
> > bool UseUnalignedLoadStores    = true
> > bool UseXMMForArrayCopy        = true
> > bool UseXMMForObjInit             = true
> > bool UseFastStosb                       = false
> > bool AlignVector                          = false
> 
> I assume you have performance numbers to justify/motivate this change.
> Can you please provide some details in the bug report.
> 
David, Thanks for the review.

1. Below mentioned 4 flags were set as default on AMD 17h too. We are just extending existing AMD 17h defaults to AMD 19h.
    bool UseFPUForSpilling = true
    bool UseUnalignedLoadStores = true
    bool UseXMMForArrayCopy = true
    bool AlignVector = false

2. Since AMD 19h supports fast string operations, “UseFastStosb” was enabled by default for object initialization. But from our experiments, XMM/YMM MOVDQU instructions performs better overall especially with respect to array sizes >16 (64 bytes) & <256 (1KB).
Attached performance data : [Perf-data.txt](https://github.com/openjdk/jdk/files/5566025/Perf-data.txt)
Test case used: I have used the same test case as in (http://cr.openjdk.java.net/~shade/8146801/benchmarks.jar) with additional sizes.

  bool UseFastStosb = false
  bool UseXMMForObjInit = true

Regards,
Rohit

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PR: https://git.openjdk.java.net/jdk/pull/1288