[11u] RFR 8245512: CRC32 optimization using AVX512 instructions

[Viswanathan, Sandhya]

Hi Christoph,

Thanks a lot for considering this. 
It is just a performance improvement for our latest x86 64-bit platform with no side for others. 
The optimization has been out for about a quarter as part of JDK 15. 

Best Regards,
Sandhya

-----Original Message-----
From: Langer, Christoph <christoph.langer at sap.com> 
Sent: Wednesday, December 23, 2020 5:10 AM
To: Viswanathan, Sandhya <sandhya.viswanathan at intel.com>; Doerr, Martin <martin.doerr at sap.com>; Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; Andrew Haley <aph at redhat.com>
Cc: Vladimir Kozlov <vladimir.kozlov at oracle.com>; jdk-updates-dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net
Subject: RE: [11u] RFR 8245512: CRC32 optimization using AVX512 instructions

Hi,

as we should be cautious about backports to an LTS release if something is not just a bugfix, I'm not sure whether this backport for a performance enhancement is good to go. Generally, if it can be proven that it's really just a potential performance improvement without side effects to other scenarios, I would be fine with it. But as I'm not an expert in this area, I'd prefer if it there was some further endorsement (or disapproval)...

@Andrew Haley; @Lindenmaier, Goetz; @Doerr, Martin, what's your assessment?

Thanks
Christoph

> -----Original Message-----
> From: jdk-updates-dev <jdk-updates-dev-retn at openjdk.java.net> On 
> Behalf Of Viswanathan, Sandhya
> Sent: Freitag, 11. Dezember 2020 00:47
> To: Vladimir Kozlov <vladimir.kozlov at oracle.com>; jdk-updates- 
> dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net
> Subject: RE: [11u] RFR 8245512: CRC32 optimization using AVX512 
> instructions
> 
> Thanks a lot Vladimir for review and link to the process. I requested 
> the backport in JBS.
> 
> Best Regards,
> Sandhya
> 
> -----Original Message-----
> From: Vladimir Kozlov <vladimir.kozlov at oracle.com>
> Sent: Thursday, December 10, 2020 3:07 PM
> To: Viswanathan, Sandhya <sandhya.viswanathan at intel.com>; jdk-updates- 
> dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net
> Subject: Re: [11u] RFR 8245512: CRC32 optimization using AVX512 
> instructions
> 
> Changes are fine but you need to follow process:
> 
> http://openjdk.java.net/projects/jdk-updates/approval.html
> 
> Also it is performance improvement which may not be accepted.
> 
> Regards,
> Vladimi
> 
> On 12/10/20 1:00 PM, Viswanathan, Sandhya wrote:
> > I would like to backport the CRC32 optimization using AVX512 
> > instructions
> to JDK 11u.
> > This optimization was introduced in JDK 15.
> >
> > JBS: https://bugs.openjdk.java.net/browse/JDK-8245512
> > Webrev: http://cr.openjdk.java.net/~sviswanathan/8245512/webrev.00/
> >
> > Only one change was needed to the original patch in
> src/hotspot/cpu/x86/assembler_x86.cpp.
> >
> > The following in Assembler::blendvpb(), line 7908:
> >
> >   emit_int24(0x4C, (0xC0 | encode), (0xF0 & src2_enc << 4)); was 
> > replaced by equivalent:
> >    emit_int8((unsigned char)0x4C);
> > emit_int8((unsigned char)(0xC0 | encode)); emit_int8((unsigned
> > char)(0xF0 & src2_enc<<4));
> >
> > The patch applies cleanly otherwise.
> >
> > Please review this backport to 11u.
> >
> > Best Regards,
> > Sandhya
> >